Wiring harness repair

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  #1  
Old 09-17-12, 09:28 PM
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Wiring harness repair

1994 Nissan hardbody D21 king cab 4x4 pickup.

Left brake light not working. It's one of those 1157's and it lights when the lights are on but doesn't get brighter when the brake is down. The other brake light works so I guess it's not hte brake switch.

The mechanic at the Nissan dealership (reliable) tells me my wiring harness needs to be replaced. It's not available so he wants to rebuild it at considerable cost.

It looks like a bunch of wires ending in sockets to me, so it seems like I should be able to trace the problem. Are there switches/relays involved or is it actually that simple?

Can someone get me started on troubleshooting this? For example, how do I test for a broken wire without somehow removing the insulation? Is there a tester for that?
 
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Old 09-18-12, 03:34 AM
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Don't shoot the piano player, but have you changed bulbs? The 1157 is a dual filament bulb and the secondary filament is the one that lights up when you press the brakes. I can't believe the dealership even suggested a new wiring harness. That's, for lack of a civil word, stupid. Buy a 12v probe and start tracing power at the light, going toward the engine compartment. You may find a broken wire. Check the connections in your bulb socket as well as the general condition of the socket itself. It won't be in the brake switch, relay, or fuses if one brake light illuminates. It will be localized to the left light unit. Those probes use a needle like end to penetrate the skin of wire, so you don't have to strip anything.
 
  #3  
Old 09-18-12, 04:16 AM
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Bulb, check not that. Thanks for the encouragement. Socket contacts seem bent but not finding a replacement.
 
  #4  
Old 09-18-12, 05:32 AM
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Worst case scenario, find a reputable independent garage with a good electrical guy to troubleshoot it.
 
  #5  
Old 10-05-12, 09:14 AM
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Less likely but possible the turn light switch is not directing current to it. Unless you have had a fire or major mechanical damage to wiring harness I would question "building new harness"
 
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Old 10-09-12, 07:28 PM
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I thought I'd let you know how this turned out. Like the last response above I also couldn't imagine what could be wrong with the wiring unless one was cut and nothing seemed that wrong. I tried testing the (1157) bulb socket with a circuit tester (more on that below), then gave that up and went ahead and replaced the socket with one made for a different import but that I made fit with a few judicious adjustments. I got lucky and it turned out it was the socket and the brake light works now. So I saved $300-$600 and thanks for the encouragement to DIY it from you guys.

Even so, trial and error is fine when it works on the first try . . . but it raised a question of how to use a circuit tester to test a socket. I attached the ground wire to an unpainted bolt, then touched the probe to each of the two (positive I thought?) contacts in the 1157 socket in turn with the lights on and also with someone pumping the brake pedal. The first time I did this I was testing on the socket that was working and it blew the fuse. The second couple of times I got thin sparking arcs between the tester probe and the shaft of the socket. Never did get the tester light to go on and that was on the socket that was working. So I guess I don't know how to use it. Can anyone offer any help here?
 

Last edited by suobs; 10-09-12 at 07:51 PM.
  #7  
Old 10-10-12, 03:13 AM
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I got thin sparking arcs between the tester probe and the shaft of the socket.
That's because the shaft of the socket is grounded, and your probe shorted directly from the hot contact to the ground. I usually place a piece of heat shrink tubing on my probe all the way to the tip, leaving only about 1/8" showing. One false move and you can ground out, so that added protection helps.
 
  #8  
Old 10-10-12, 09:11 AM
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Try your test light across the batt to make sure it is not lying to you.
 
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