Rear Light Problem

aczlan · Jun 27, 2009

wingbone said:
The converter is brand new and I've actually tried another I scavenged from on old Chevy Venture harness. My truck lights are the exact same lights as my trailer lights.
White=Ground
Red=Stop/Turn
Black=Running lights

Truck has individual wires for:
Stop
Left Turn
Right Turn
Running lights

My original problem was how do I hook the truck's stop light wire to both lights without having them bridge when either turn signal is used. This is when Diamondpilot told me I needed the converter, which makes sense to me. I tried the harness I already had and couldn't get it to work so I thought maybe it just wasn't designed to do what I wanted to do. I went to Walmart and bought a 5 wire to 4 wire converter that is supposed to do exactly what I'm looking for, but it behaves exactly like the harness I already had. This makes me think that it isn't just a bad unit since they are doing the same thing. I guess I'll have to take it back and exchange it for another just to see. I'll test the next one with a meter before I ever hook it up to any power source.This seems like it should really be an ultra simple task, but maybe I'm doing something stupid.

Thanks for clarifying things, I must have missed that earlier. Are the truck lights currently working? (IE: If you hit the brakes on the truck do you get 12v on the brake wire and do you get 12v on the turn signal wires when you turn them on?). This is a real headscratcher, it sounds like you are doing everything correctly, but it doesnt want to work.

Aaron Z

wingbone · Jun 27, 2009

When I check the wires all individually on the truck, they are all getting power when checked with a circuit tester. The problem occurs when I try to hook them to a converter. I'm not even going to hook back up to the truck until I can get it worked out with a meter or get it to work with my battery/spare light set up. I'm going to exchange the converter I bought and check it with a meter before I hook up any power to it, this should at tell me I'm not frying in somehow. When I first check it with a meter, shouldn't I get '0' ohms resistance if the circuit is complete? I checked continuity of the ground and running light wire and got '0', indicating a good circuit and these also powered my spare light. I should be getting this when checking the others as well, but I haven't. I about to leave for vacation in a couple hours, so it looks like it will drive me crazy all week thinking about it. I do plan on taking my meter and exchanging the converter, I can at least check that while I'm away. Thanks for the input so far.

herringchoker · Jun 27, 2009

What is your dump truck? Is it a Class 8, like a highway tractor? These may seem like stupid questions, but the large trucks are wired to have combined stop/turn signal lights on the truck/tractor itself but separated stop & turn signal lights on the trailer. (Notice that semitrailers have separate brake and turn signal lights.) The wiring conversion is done in the turn signal switch on these rigs. If you have a truck wired this way, are you trying to feed the trailer from the pre-wired trailer feed on the truck (which would be the obvious thing to do

)? If so, what you need to do is feed directly from the tail/stop/turn signal lights on the truck.

George2615 · Jun 29, 2009

Wingbone,
If your truck lights are working properly then you only need to hook up 4 wires for basic trailer wiring.

hook the left turn signal wire on the truck to the left turn signal wire on the trailer.
hook the right turn signal wire on the truck to the right turn signal wire on the trailer.
hook the parking light wire on the truck to the parking light wire on the trailer.
hook the trailer ground wire to the truck ground.

If you hook these 4 wires like this your trailer brake lights will automatically work just like the truck. You don't need to hook up a separate wire for brakes.

If you wire as described and they don't work correctly the the trailer wiring is not wired correctly.

The only reason you would need a converter is if your truck brake and turn signal lights use different bulbs but based on your description in post 5 you have a red, white, and black wire at each light. This tells me your truck lights each have one bulb with dual filaments. One filament is used for parking lights and the other for brake and turn signal.

firemanpat2910 · Jun 29, 2009

"I had a small gel cell 12v battery that I used to hook directly to the individual wires on the harness. I had a 4 wire connector coming out the other side of the harness hooked directly to an extra, new trailer light I already had. The running light worked just like on the truck but the others would not do anything. This experiment is completely away from the truck done on a table. I tried all combinations of hooking the red/green/yellow wires individually and together and could not get them to do anything. Still only the brown running light would work in this manner. I don't know how much simpler it could get than doing it like this.[/QUOTE]"Most trailer light issues are ground related. Bad/wrong bulbs are #2, BAD WIRING #3 I would try this: take the plain flat 4 that goes to the trailer set meter to ohms for a continuity test. one leg of meter to white wire, other leg to ground on trailer, then ground on light bracket

firemanpat2910 · Jun 29, 2009

then leave connected to the white and touch other lead to the tail light lead, should be the brown wire, according to what you have sai they work so there should be continuity all the way from white to brown. now try from white to green or yellow, if you dont get continuity then try leaving meter hooked to the green or yellow and go to metal ground, then to light bracket, then to light/bulb socket, when you find continuity back step one till you loose it go forward till you find it in between is your problem. I will bet it is a ground some where. sometimes you have to add your own grounding to the bulb/ or bracket to ground both tail and brake/turn curciuts..

wingbone · Jun 29, 2009

LET ME CLARIFY. These are the lights for my truck!!!!
I have:
Stop light wire.
Right Turn wire.
Left Turn wire.
Running lights wire.

I bought a 5 to 4 converter. It has hook ups for these wires plus ground and is supposed to combine the brake and turn signals together. I've bought yet another converter and tried to check it before hooking it up to the truck to make sure I wasn't frying it. I still can't get continuity except on the running light wire and ground wire. There must be some simple think I'm overlooking. This thing only has five wires going in and five coming out.

aczlan · Jun 29, 2009

wingbone said:
I still can't get continuity except on the running light wire and ground wire. There must be some simple think I'm overlooking.

I don't know if you can get continuity through a 5-4 wire adapter, IIRC a few years ago when my brother was going to install a used one on my sisters car he called me (quite worried) because he wasn't getting continuity from brakes/turn on the car side to the trailer side, I told him to hook it up and see if it would work as it had worked fine in the car it was in before, he hooked it up and it worked.
My memory may be off some (it was a few years back), but I am relatively certain that it worked but he couldn't get continuity with a meter.

This thing only has five wires going in and five coming out.

hopefully it has 5 in and 4 out

Aaron Z

wingbone · Jul 6, 2009

Well, I believe I got the lights working. I was mistaken saying the turn and brake signals were independent, but I had a little 'help' in believing so. The truck has an aftermarket turn signal assembly(Grote 48272 I believe is the model). It has about 8 wires coming out of it including a brake signal wire. Where I really got messed up was due to the fact there is a wire going to the rear of the truck, which to me is really useless. The previous owner may have had some reason for it, but I don't know what it could be. I found out by touching this brake wire to either tail light, both would light up, so I knew for sure it was being controlled up front somewhere. Obviously, something was still not hooked up right because the turn and tail lights still weren't working. I remembered from looking up the aftermarket turn signal on the net that there was a brake wire coming out of it. I had previously experimented with this wire last week but apparently didn't figure out exactly how it was supposed to be hooked up. Just guessing, I went ahead and tied this wire in to the cold side of the brake pedal light switch and Eureka, that was the problem. The aftermarket turn signal is where all the magic is taking place. Whoever had this before me did not have this wire tied in. I found out the brake signal wire at the back of the truck is also tied in to the cold side of the brake pedal switch, but I can't see how it would have worked on anything unless there had been an extra set of lights just for brakes at the rear. Anyway, thanks for those who helped me and I'm sure this sounds like a bunch of mumbo-jumbo to those reading it without being able to see it first hand.