Rewiring a vehicle

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When completely rewiring a vehicle there are a few things that must be determined beforehand. First, one must decide if a prefabricated harness will be used, or if a custom harness will be made from scratch. In any case the harness should be assembled into groups and cut within a reasonable distance to the right length, while leaving extra wire to account for routing.
 
  
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Next one must have the tools and supplies required for the job. Here is what is required:
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==Overview==
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When completely rewiring a vehicle there are a few things that must be determined beforehand. First, one must decide if a prefabricated harness will be used, or if a custom harness will be made from scratch. In any case, the harness should be assembled into groups and cut within a reasonable distance to the right length, while leaving extra wire to account for routing.
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==Scratch-built harness==
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If you intend to scratch-build your harness, will need a few things from the garage:
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#A pair of sawhorses
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#One or two 4 X 8 Sheets of 1/4 or 1/2 inch plywood.
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#Some nails about 4 inches long.
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If you have a two-car garage you can afford to tie up for a few days, set your sawhorses up next to the vehicle to be wired, and join and place your plywood on top of them. You should now have a platform about the size of the vehicle to be wired.
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#Get a magic marker, and draw a rough outline of the vehicle side-to-side, front-to-tail, with lines for firewall, dashboard and trunk spaces on your plywood.
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#Measure and show headlight locations as well as tail lamp locations.
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#Next, studying your vehicle, determine the course of harness routing and areas of location for the fuse buss, battery, dash, engine bay harness, and all locations for electrical plugs and devices. Make a rough drawing and take measurements from point to point.
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#Transpose the drawings over to your plywood. Draw a line to show routing, and, at each termination point, drive a nail about 1/4" in your wood, and mark its function (tail, left, etc.). Place your plug/socket and pins there (for later..). Continue until you have all termination points laid out and represented by a nail on the plywood.
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#Next, figure out your wire gauge for each circuit, as predicated on the draw and length of the run. Make a list (EXAMPLE: Tail Lamps...21 Feet...10 amps...14 gauge black). Your best bet is to make the wire longer than you would expect to use. Add a few feet or more than you will actually need. This will help when finding mistakes or having to cut your terminal off and starting over.Plus, if you measured incorrectly, or have to route around something, you will not need to splice the wires together.
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#Now, starting with your smallest gauge, at the buss, tie the wire there, run it down your marked route line (addeExtra length for anywhere it must rise or fall within the body) to the nail marked "Tail lamp" then mark the wire with a wire marker (available at any hardware store). Mark the function and number on your notes, and continue the "wrap" along to the next item (like the right lamp etc..). Do not cut until the wire reaches termination. Continue until all color wires of that gauge are laid out. Then, repeat with the next largest gauge wire, until all wire is laid out nail to nail. Be sure to keep your runs straight and tight, and do not cut the nail ends until ALL wires are in place. Add 5 "Spares" and mark then as such the length of the harness -- for future expansion or in case you shoot a screw through one and get a bad wire.
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#Tie the bundle up neatly with proper tie wraps nose to tail.
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#Cut all nail ends at an equal distance, referring to your notes, and wire markers, as to function and number. Add your firewall connectors/sockets, fuse buss and devices.
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#Lastly, using a DVOM or "Ring Box" Ohm or ring the harness out point to point for accuracy. Correct any errors, and you should be ready to fit it to the vehicle.
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==Tools and supplies==
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Here is what is required for the job:
  
 
*Wiring harness
 
*Wiring harness
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*Black wire
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*Black wire (for grounds)
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*Wire strippers
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*Wire, various Colors (red/white/green/brown/purple/orange/) -- various gauges.
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*Good quality wire strippers with depth gauge.
 
*Crimpers
 
*Crimpers
 
*Connectors
 
*Connectors
 
*Electrical tape
 
*Electrical tape
 
*Wire loom
 
*Wire loom
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*Wire markers
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*Adel clamps
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*Anti-chafe
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*Rubber matting
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*Pliobond adhesive
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*Grommets (various sizes)
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*Electrician's putty
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*Plastic conduit (chrome or black, or any color)
 
*Rubberized wiring hooks (may not be needed in some cases)
 
*Rubberized wiring hooks (may not be needed in some cases)
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*Tech or self-drilling screws.
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*Star and lock washers (various sizes)
 
*Sheet metal screws (may not be needed in some cases)
 
*Sheet metal screws (may not be needed in some cases)
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*Wiring diagrams are very helpful too
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*Accurate wiring diagrams, as well as YOUR notes and drawings made for the new system to be installed.
  
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===If soldering:===
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If soldering:
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*Good soldering station (don't use an undersized or non-controlled unit; it will slow things down)
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*Good soldering gun (don't skimp and use an iron; it will slow things down)
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*Solder (24 gauge 60/40 is good)
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*Solder
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*Resin
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*Desoldering tools, and braid
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*Heat gun
 
*Shrink tube
 
*Shrink tube
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*Hemostats
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*Dental pick
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Read [[How to solder electrical connections]] if you are unsure how to do so.
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==Harness removal==
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Next, the wiring harness in the vehicle must be removed. A digital camera and note pad are your best friends here. Photograph EVERYTHING -- even if you think you won't need it later. Be sure to label every disconnected or cut wire as to its original location, and as you do this, add its location, colors, gauges and functions to your notepad.
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Keep the original harness intact as possible and UNPLUG EVERYTHING YOU CAN. Keeping this harness intact can help with understanding how things were wired in the original configuration before the routing of harness wire. Once that is complete, you are ready to begin installation of your new harness.
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==Installation of the new harness==
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Once you have your wiring harness and your old wires removed, your first step is to install the fuse block. Many fuse blocks connect to the factory bulkhead connector with bolts; in other cases, the fuse block may need to be screwed or bolted to the firewall or another secure location. If the fuse block is a firewall pass through type, SEAL the edges with a GOOD water, dust and vapor type sealer, OR electricians putty.
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#Begin routing your wires. While doing this, keep in mind any sharp areas that may sever a wire. Wherever you encounter such an area, install rubber matting, anti-chafe or a proper grommet to the area, and secure the wires as well as possible using a rubberized metallic Adel clamp, tech or sheetmetal screw and lock washer. This procedure will prevent the wiring from deteriorating from vibration and stress chafing.
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#Begin by routing your longest wires first and working in a counter-clockwise fashion working back to the center (firewall). Make notes and drawings that correspond to your routing/wire functions, and any special items that may require attention.
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#Locate all your remote ground areas, such as headlight and tail light buckets, fuel sender/tank grounds, and any local grounding areas. Clean and burnish all paint, dirt, and grease from these areas, install a proper ground, using a star washer, lock washer, tech or sheetmetal screw.
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===Build and install the ground buss system:===
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#Run a proper-gauge ground cable (4 gauge or better) from the battery to any handy bolt at or near the starter. From that same bolt, get a battery cable at the parts store that has two 3/8" ring terminals on each end and attach it there and to the frame, following the shortest run possible.
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#Next, get some 10 gauge wire and ring terminals, and run that from your bolt on the block to the firewall, and another to the alternator bracket or mount bolt.
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#Next get some wire braid, (electronics store) and install braid from the radiator support to the frame, fenderwells to frame, hood to firewall, doors to door posts, gas flap to body, gas tank to frame, tailgate/trunk to body.
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#At each point the wire is grounded, burnish ALL the paint and grease off to bare metal. Use a proper star-washer and lock. Use sheetmetal or tech screws where no screws are available.
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#When done properly, all the grounds in the buss system should terminate at the same mount point AT or NEAR the starter.
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#Once these wires are routed and secured, you can begin attaching the device wires to their devices. The following order is recommended: tail lights/fuel gauge sender, headlight/horn, engine compartment, interior lights/speakers, power windows and locks, heater and stereo, dashboard.
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#Keep in mind that certain connectors are not easy to find new. Therefore, in some cases you must solder or crimp an old pigtail onto the new wire. To do that properly, set up your soldering station, heat shrink gun and tubing, and your other soldering hand tools in the area of work.
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#Measure the wires from the device, as well as the wires from the harness to overlap about 3 inches in each direction (leave enough wire slack for devices like lamp sockets that must be removed to change a bulb, etc.). Then, trim and strip so they will overlap about 3 inches, add shrink tubing to the wire, sliding it FAR enough back so as not to prematurely shrink it with heat from the solder joint. Then wrap your wire, first clockwise, then counter-clockwise until you have a good SECURE mechanical joint (tug test it).
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#Trim excess "whiskers" from it and smooth as well as possible. Then apply heat and solder to the wire. Heat at one end, solder at the other, and solder until it flows from one end to the other. Do not "glob" it; it should resemble the bare wire, except be silver.
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#Inspect your joint. It should cover the bare wire 360 degrees, from insulation to insulation. Insulation should not be burned or charred (if so, reduce tip heat) and be bright silver to be a good joint. If it is a dull gray, you have a "cold solder" joint that will corrode, crack and not properly conduct; start the process again using more heat or heating time.
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#If satisfied with your joint, slide your tubing down over the joint, and, using your heat gun, shrink it down to its proper gauge. Hold the wire straight until it has cooled or it will take on the "droop" of the angle it had while cooling. If you need a pre-bent joint, hold it at that angle until cool -- it will maintain that angle.
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#Continue soldering the rest of your device/harness connections until complete.
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#Inspect your work. Be vigilant for chafing problems, good insulation, proper bonding and soldering. Add Adel clamps where required, (for proper strain relief, attach an Adel about 3 inches from where a harness must exit or enter a bulkhead, make a curve, or attach to a device). Check for proper clearance from heat-producing parts, and rotating parts, fuel and hydraulic lines, or anything that can hook and cut the wire.
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#Now is a good time to clear the work area of tools, excess wire, parts, anything that can heat and burn you or the harness (like soldering irons, heat guns, etc.). Then sit with your notes, and make a line drawing. Start with a single line which will be a power buss, then run a line from it to the fuse to the switchgear, to the device to ground.
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#Do the same for the whole diagram. You can get software to make your own schematic on your computer. This is where all your notes and line drawing will merge into a single easy-to-read schematic, which will be useful in the future.
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#Next, one last time, ring or continuity check your harness point to point with an OHM meter or ring box. Make sure your connections are correct, and conducting, and conform to your line drawing (you can do both steps at the same time). Once you confirm all is correct, you can power test the system.
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==Fuse requirements==
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For heavy draw accessories a [http://www.crankshaftcoalition.com/wiki/Relay_application_guide-_Bosch_relays '''relay'''] is the preferred method of wiring a circuit. Some things that can benefit from a relay:
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*Headlights
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*Cooling fans
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*Fuel pump
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For circuits having a high draw a circuit breaker may be substituted for a large capacity fuse.
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;Basic fuse requirements (from [[Media:Harness inst painless.pdf|Painless wiring]]):
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{| class="wikitable"
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|-
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! Accessory  !! Amp!!Accessory!!Amp
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|-
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|Headlight switch||30||Radio (constant)||10
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|-
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|Coil||30||Wipers||15
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|-
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|Door lock||20||Radio (switched)||10
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|-
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|Cigarette lighter||20||Backup/cruise control||10
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|-
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| Horn||20||Gauges||10 
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|-
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|Brake switch||20||Dome/Trunk light||10
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|-
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|Power windows||20|| Power antenna||10
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|-
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|Turn signals||15||Electric fan relay||5 
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|-
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|Emergency flashers||15||AC/Heat relay||5
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|-
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| Electric fuel Pump||15 
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|}
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The fuse requirement and wire gauge has to take the accessory load into consideration. Using too small of a wire can let a wire burn even though the accessory load matches the fuse rating. Using too 'big' of a fuse can let a wire burn even if the wire gauge matches the load.
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==Testing==
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Some people recommend a battery charger to test with. While a Battery charger will run a DC motor or lamps quite well, they are NOT well filtered! They (usually) consist of a 1/2 wave rectifier system with no capacitive filtering. This means 30 Cycles of the 60 cycle AC from the wall plug escapes into your system, creating a "ripple" in the DC. Again, not a problem in a motor or lamp, but can destroy a digital radio, amp, ECU, ECM, some alternators, some regulators, and the like.
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The first recommendation is a bench supply that has a current adjustment as well as an adjustable voltage control, is fused, and regulated. Not everybody will have one, or be able to afford one. Try borrowing one; it allows you to apply power with the current and voltage controls at zero. You can then adjust the voltage to 14.2, then slowly bring up the current. If you have a short, the AMP meter will shoot up rapidly, as you apply small amounts of current. In this manner you can turn the supply off LONG before ANY damage will occur, and correct the problem, AND if it exceeds the maximum draw for the supply, it will trip the fuse.
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The second recommendation is a motorcycle battery (not a big Harley batter, a small hold-in-your-hand Honda-type battery). Install a 30 amp fuse link on the positive, and, (if your meter supports it) use your meter in line to monitor current. At this point you will be doing no "high current testing" so you should be good. If not a motorcycle battery, two parallel connected lantern batteries should last long enough to do some primary testing.
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If you must use a battery charger, disconnect ANY electronics you have: CD player, tach, ECU, ECM, alternator, regulator, digital dash displays, and anything solid state to avoid damage.
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Whatever system approach you take, test for functionality, correct any errors you may find.
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===Testing a brake switch, etc.===
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*Set the meter to the 20 VDC volt scale (or whatever is close to that).
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*Ground the negative meter lead, then probe the wires separately. In the "at rest" position- brakes [B]not[/B] depressed- there should be power IN but not OUT.
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*With the brakes depressed there should be power at BOTH terminals.
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**If there is no power IN, the wire has burned or the fuse blown, or the wire has been disconnected.
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**If there's power IN to the switch but nothing OUT with the switch activated, you have a bad switch.
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*You can also test the switch using the ohm setting, be sure to disconnect the switch from the wiring first. Connect the meter leads, one lead to each terminal. If the switch is OK, you should have continuity (close to zero) with the switch activated (brakes ON), and infinity with the switch at rest.
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**If you have a high ohm reading w/the brakes ON, or infinity, the switch is no good.
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==Miscellaneous==
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One must realize that many times you will supply power to a circuit (i.e. tail lights), and other times you will supply a ground, as the circuit have power supplied directly to them, and the ground is what is switched. This is very common in courtesy lights that are grounded when the door switch is activated.
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Sometimes you must use existing wires (as when they go from the dash, up the A-pillar, across the top, to a courtesy (interior) light. These are seldom removable if you have the headliner in place. Use a test device to be sure there are no shorts or 'opens' (broken wires).
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If you are changing from 6 to 12 volts (a very good idea), your new wire does not have to be as large as the original, as the current will only be 1/2 the original. This can be important when buying wire in several colors. You can often do much of the wiring using 14ga wire, or even 16ga, but be sure to determine the current draw before committing to a particular gauge of wire. Also, if you use LED lights, the current is minscule! And, they generate no heat to speak of.
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Sometimes a custom harness will be cheaper, especially if you want to use factory color codes.
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Furthermore, it is suggested that a maxi fuse is installed rather than a fusible link. A lot of this is personal preference. However, it is too easy to pop a new maxi back into the socket and avoid the REAL problem -- what took it out? A fuse link MUST be cut, repaired, soldered and heat-shrunk back into place to be repaired. This will motivate you to look into WHY it went out.
  
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Next, the wiring harness in the vehicle must be removed. Be sure to label every disconnected or cut wire as to its original location. Keep the original harness intact as possible and UNPLUG EVERYTHING YOU CAN. Keeping this harness intact can help with understanding of how things were wired before the routing of wires. Once that is complete you are ready to begin installation of  your new harness.
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Fuse links, unlike fuses, do not just blow -- something major is wrong! And, it was wrong long enough to melt wire -- unlike a 5 amp radio fuse that sees a 7-amp spike and opens a few times a year. It took a 50, 70 or 100 amp short of a few seconds/minutes to melt the link -- not a small issue. Find out why!
  
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In either case, a maxi and fuse link do the same job -- a 70-amp maxi is the same as a 70-amp link. What is important on either is to never install them inside a passenger compartment. They do their job by heating and melting, and can cause fires to interior parts, melt plastic parts, and create toxic fumes in a closed compartment. Always install them in the engine bay away from fuel, hydraulic, or other flammables.
  
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Once you have your wiring harness and your old wires removed, your first step is to install the fuse block. On many vehicles this is as simple as placing it in the factory position.
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While some wiring harnesses recommend the main power come off the starter live connection, running the wire straight to a single insulated battery terminal post can be a better way to go. Such a case would be an off-road vehicle where water or mud could cause problems if the main power wire is connected to the starter.
  
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The next step is to begin routing your wires. While doing this keep in mind any sharp areas that may sever a wire and secure the wires as good as possible. This will prevent the wiring from deteriorating as quickly as they would if little care is given. Begin by routing your longest wires first, as, quite often they will get in your way while dealing with the shorter wires.
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[[Category:Ignition]]
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[[Category:Electrical]]

Latest revision as of 21:50, 1 January 2024

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