I am trying to add additional reverse lights to the truck. The truck has the 4-pin trailer harness and the 7-pin trailer harness. After getting the 7-pin working (installed the supplied relay and changed out a crap load of fuses) I figured that I could jump the power off of the 7-pin as well as the switch for the reverse lights. This would all be installed through a relay so that when the truck was in reverse the lights came on.

Well, I got everything mocked up and left a lot of wire slack and tested the "system" before buttoning it all up and it worked perfectly. When doing the final install, I shortened some of the wires and tried to find a place to mount the relay. Now the "system" does not work.

I have power in the line going to the relay and the line for the reverse lights has power (switched) when the truck is in reverse. The lights, however, do not come on. The only other thing that I did between the mock up stage and the final stage was to install the relay to the same stud that one of the lights is on and also grounded the relay to this same stud. This stud also has the independent ground of the auxiliary light (so it has or had two grounds, the light, and the relay mounted to it).

My question is what could the problem be? Could I have "broken" the relay by installing it to the same stud that is grounding the relay? I tried to ground it elsewhere after the fact, but still nothing? I suppose I will check to see if I have power coming out of the relay to supply the lights next. I also am thinking about buying a new relay. Do I also need to mount the relay somewhere that has no ground wire as well?

Thanks in advance all and I look forward to any opinions.

 

If you have power going to the lamps when the truck is in reverse, but they do not work, sounds like the ground for the lamps is no good.

Test for power at the lamp connector, using that power and ground to see if it is OK. If you meter power at the lamp connector, the only other thing is a problem with the bulb ( moved it while it was hot, filament broke ).

You posted the relay is switching power to pin 87 when the truck is in reverse, so the relay is operating correctly ( if I understood the post correctly ).

 

Thanks for the reply Scully.

I have power both Battery and Switch going to the relay when the truck is on and in reverse. When I did the initial setup, everything worked. After I confirmed it working, I cut/shortened the supplied wire as it was all way to long. When I finished up, the lights no longer worked. The lights were not moved or touched between the initial setup and the final setup, so I think that the bulbs are ok and the grounds are still good.

I still have Battery Power and the Switch Power but the relay doesnt seem to have the power out to the lights.

Could I have shorted out the relay by grounding it to the same stud it was mounted to?

 

OK, I misread your post.

1. The "switch" power is the reverse lamps, to trigger the coil ?
2. You have power to the relay, but none leaving the relay ( power on pin #30, but none of pin #87 ).

Check the ground on the relay, to make sure it is good. Use a meter to check resistance to something like the trailer tow adapter plug.

If you have pin #30 & pin #85 good at the relay, pin #87 will be dead, without ground on pin #86 ( you could have pins #85 & 86 reversed, unless the relay has a built in diode to stop field collapse ).

Check the female terminal / relay socket for ground.

 

Got it figured out at lunch time today. The problem ended up being that the wire to the lights had slipped out of the connector, hence no power to the lights. Also, there was power coming out of the relay but the connector there (the supplied one with the lights) was a bit to big and was making intermittent contact, at best. Replaced the connector and got a nice solid crimp on the other connector and now everything works like it should.

Thanks Scully for your efforts.