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Old 05-23-2022, 05:12 AM   #9
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Originally Posted by bigdog View Post
Circling back with some testing I've done...
I tried testing the trailer connection on the truck with a volt tester, but couldn't get 'any' from any of the four connection connection leads. I would think I would be able to get 12v by connecting my voltmeter lead to any one of those harness pins and voltmeter ground lead to ground, but I got no reading ?

Next steps is to check fuses in truck pertaining to trailer, there are three.
25 Amp trailer tow park lights
20 Amp trailer tow stop-turn-relay fuse
25 Amp trailer tow lamps module

Not sure one can actually test for a bad fuse ? Continuity check ?

Your feedback would be greatly appreciated !
You say the directional and stop signals are working so SOME of the connector leads SHOULD be giving you a reading.

Are your tail lights (not direction/stop) working on the back modules? If so, you have a wiring problem on the trailer to the side and license lights which are on the same feed as the tail lights.

I would make sure your "ground" spot for the voltmeter is good. A lot of metal on cars does NOT make a good ground and you will get zero voltage with a bad ground. You could try the ground connector with on the car side trailer connector however that itself could be the problem. Start with the directionals that you say are working. If they are not showing on your voltmeter test, you are doing the test wrong/have the meter set wrong/have a bad ground.

Next, I suspect the fuses are not specifically for the trailer. They are for the light circuit in the truck. If the truck lights are working the fuses are OK. The trailer lights generally use the same fuses as the truck lights.

Next I would suspect a bad/poor connection between the car and trailer connector. Have you cleaned the leads (on both sides) recently? Once the leads are clean AND you have a signal on the car side connector, if you have a sharp pointed lead on your tester you can poke it through the insulation just past the connectors on the trailer side to see if the signal is going through. AGAIN, a good ground is essential.

If the signal is getting past the connector junction, I would jump to the bulbs themselves. Bad/dirty socket? Burned out bulb? You can use the voltmeter to test the power to the socket. AGAIN, make sure you have a good ground. Test a working light (turn) first. If you can't measure voltage you don't have a good ground or don't have the meter set correctly.

After that, wires between the connector to the socket. Pinched and broken? Gnawed by varmints?

Essentially, start at the car side and verify the power for each light is getting through at each point along the way. BE METICULOUS. If you are sloppy you could spend hours chasing your tail.
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