Trailer Lights Gurus--Got a Question.

[Bearsixty7]

I would test the plug on the pickup with a DMM and see if it got the same signal that the vehicle lights did, that should isolate the issue.
You can also test the trailer with a 12v source (like an old power supply from a computer, who doesn't have a few of them around) and confirm that they work as they're supposed to.

Or just an old automobile 12V battery or even a Cordless tools battery if it's 12V. I have used my old DeWalt 12V batteries to test trailer lights.

I would start with a DMM at the truck connector for the trailer. Should be Ground, Left turn, Right turn and Tail/clearance lights. None of these will have power until activated. Truck tail/clearance lights on = trailer tail/clearance lights on.
Truck Turn signals=trailer turn signals.

 

[Bearsixty7]

It sounds like the White (Ground) and Brown (Tail) wires are crossed up at the trailer connector or where they are connected in the truck.

 

[npalen]

Sounds to me like the truck's trailer wires are not connected properly. Does the same truck hooked up to a different trailer, work properly?

Need to try that.

 

[npalen]

I would test the plug on the pickup with a DMM and see if it got the same signal that the vehicle lights did, that should isolate the issue.
You can also test the trailer with a 12v source (like an old power supply from a computer, who doesn't have a few of them around) and confirm that they work as they're supposed to.

Yes, have done this using a 12 VDC booster pack and getting all the signals that the trailer needs to work, as long as the pickup lights are on. Nothing with the pickup lights off, however, just as the trailer lights see.

 

[npalen]

It sounds like the White (Ground) and Brown (Tail) wires are crossed up at the trailer connector or where they are connected in the truck.

Checks correct with a DMM. White is negative and brown is positive.

 

[MossRoad]

You can get a 4-wire trailer light tester from most auto parts stores, Harbor Freight, etc., for about $6.00. They work really well.

 

[npalen]

Sounds to me like the truck's trailer wires are not connected properly. Does the same truck hooked up to a different trailer, work properly?

https://www.autozone.com/electrical-and-lighting/trailer-wire-harness-and-connector/p/hopkins-trailer-wire-harness-and-connector-42115/70600_0_0

The pickup does not have a "factory" 4pin trailer connector so the above is what I used several years ago to give the pickup trailer light capability. It's possible that something is connected improperly in this aftermarket device.

Another thought I'm having: Is it possible that there is a fuse receptacle in the truck that didn't have/never has had a fuse installed from the factory? In other words, the trailer lights work fine as long as the pickup lights are on but there is a seperate fuse that provides power to the trailer when the lights are OFF. Will do some Sherlock on that possibility.

 

[npalen]

You can get a 4-wire trailer light tester from most auto parts stores, Harbor Freight, etc., for about $6.00. They work really well.

Will plan to do that. I see there is one available that has both 4pin and 7pin testing capability.
I'm afraid, however, that it will indicate the same thing as the DMM and the connected trailer indicate; no power with pickup lights off.

 

[herm0016]

GM used to ship the +12 wire on the 7 blade disconnected at the fuse block, but the lights should still work properly with out the +12 power hooked up.

 

[npalen]

GM used to ship the +12 wire on the 7 blade disconnected at the fuse block, but the lights should still work properly with out the +12 power hooked up.

Fuse Box Diagram Dodge Dakota (2001-2004)

Fuse box diagrams (location and assignment of electrical fuses and relays) Dodge Dakota (2001, 2002, 2003, 2004).

fuse-box.info

Scrolling down towards the bottom of the above page shows the engine compartment fuse diagram. I checked and there are no fuses installed in my pickup in slots C and T with both labeled in the diagram as "TRAILER TOW CONNECTOR".

I'm taking bets as to whether the trailer lights will be active without pickup lights on when I install fuses in these two slots.