weird electrical problem; reverse lights

[grey wolf]

I'm not sure where else to post this. When I got my truck, the reverse lights weren't working (I have a C1500 short box regular cab, 4.3 with manual trans). So I got to looking into it today. Someone had the reverse switch on the trans disconnected and taped up. However, when it is connected, as soon as I turn the ignition on, the #16 fuse in the instrument panel fuse block blows (that's the turn signal/backup fuse, 20A). Now, here's where it gets weird... The connector for the reverse light switch has a pink wire and a light green wire. The pink wire should have 12V in "run", and the green wire goes to the light bulbs and to ground. With the ignition off, the pink wire is grounded, like it is shorted to ground. But with the ignition on, I have 12V. The green wire all the way to the light bulbs is fine, no shorts or anything. So, basically I have something going on between that #16 fuse and the pink wire going to the reverse switch connector. The power side of the circuit up to the reverse switch.

Confused yet? Hopefully I explained that well enough. Anyway, the only thing I can think of is that there is some kind of weird short going on at the C100 connector. That is the only connection point on that pink wire between the fuse and the connector for the reverse switch. Have any of you guys seen weird things happen with that C100 connector before? I haven't gotten around to looking at that connector, since it is buried under a bunch of crap. The harness going from the transmission right up to that connector looks like it is ok though, nothing damaged at least. I don't get how I can have 12V with ignition on, and ground with ignition off... Must be some kind of short circuit, maybe related to corrosion at that C100 connector.

 

[CarolinaContingency]

That’s a little confusing there. Ain’t gonna lie. Your pink wire should be for the brake lights, your lighter green wire should be reverse lights, and your ground should be black. Should have a brown wire in there as well. And darker green and yellow for turn signals (I’d check these in relation to your fuse.) If memory is serving me right.... been a minute since worked on mine.

That said, after I replaced my stock lights I had nothing but issues with that connector. Mine would constantly lose contact and flicker religiously when I’d go off road, or hit a pot hole.

Now here’s the other issue. Aftermarket circuit boards, Dorman in particular, kept warping on me. I replaced my circuit boards two times before I finally realized the bulb heat was causing them to slightly warp and lose contact because the center bulb was too hot. Easy way to see if this is what’s happening - pop your circuit out with bulbs in, turn your key to on with tail lights on, and lightly bend your circuit back and forth some. If it’s the circuit board it’ll regain contact when you bend, light comes on, and congrats you just need a new circuit panel. I finally had enough of that and just went ahead and decided to put in LEDs that we’re plug and play. Hope that helps some.