These instructions work for all rear lamps: brake, reverse, tail, and flasher, and can be adapted to front and other lamps. Basically, you need a multimeter or volt-ohm-meter (VOM) and it has to have settings for direct current 0-20V and for electrical continuity. (A multimeter would also have amps, generally up to 10A, which can be useful but not for this task.) The voltage setting tells you the volts in a circuit. The continuity setting tells you power is getting through a wire or connector or switch. It's helpful if the continuity setting beeps. Usually these meters take 9V batteries and you need to know how to test the meter and probes to make sure they are working. The probes need to located in the correct socket for each test. All this is usually in the meter's instructions. You also need a high quality 12V test lamp, which is usually a device shaped like a screwdriver with a sharp probe end and a wire with an alligator clip on the end. You test these by putting the probe on one side of the vehicle's batteries and the alligator clip on the other. Two long bits of heavy wire with alligator clips on each end are also helpful. Ten gauge multicore wire is best, but long jumper cables can be used too. If only one rear light is bad, start by removing the rear lamp housing and check the bulb. If both are bad, check the fuse before you do anything else. If it's fried, replace it and hope for the best, but keep checking the lights periodically for a few days because you don't know why the fuse fried. If there is only one bad light on one side, start with the the bulb(s). If they are incandescent, check the filament to make sure it's there. Compare with the other side. If they are LED look for discoloration. Then test the bulbs using the long wires to jump to the battery. Make sure they work. If they don't, replace them and you may be done. If they do, turn on the switch or apply the brakes or put the car in reverse with the ignition on but engine off, whichever applies. Check for 12V at the empty lamp unit bulb holder with the switch on, using the test lamp with the alligator clip attached to a known good ground, which could simply be your long piece of wire routed back to the battery negative. It doesn't matter for now if you don't know which bulb connector is the hot and which one the ground. Just test each one in turn. If the test lamp lights, remember which connector it was, put the bulb back in, and find a way to jump the other connector back to ground. If it lights, repair the lamp housing ground. If the test lamp doesn't light at any of the bulb holder connectors, start using the sharp probe on the end to work back through the wiring methodically to find the missing 12V. This probe is designed to push through the insulation on wires to test for power. It can also probe connectors. At this point the wiring diagram starts to become useful. Somewhere back in the harness you will find 12V and then you can repair the wires back to the bulb holder by "sistering" or replacing wires or replacing connectors. I try to use the same color and gauge of wire and rating of connector, but it's ok to go up a size if you have to. Never go down. I keep a collection of good new and used wire and connectors. I also have a heat gun and a selection of heat shrink connectors and heat shrink sheath to repair harnesses well so they can keep working in wet and salty conditions. If you are really unlucky it will be the switch in the cab (or the brake pedal or transmission reverse switch). These can be bought new or sourced at a salvage yard or online salvage operations. You can get usually get an entire fuse/relay box from a salvage operation with the fuses and relays still there for fifty or so bucks, a good investment for owners of older vehicles. In general, you just need a logical mind and some gumption and you can trace just about any electrical fault. It's certainly not the hardest job you can do on a vehicle, and you stay cleaner than you do with other kinds of wrenching.
No comments:
Post a Comment