Hi All,
I own a 1994 F250 IDI Turbo with trailer lighting issues.

Running lights work great on the trailer when the headlights are on. However the turn signals, brake lights, and flashers are very, very dim with the new LED trailer lights I purchased to replace the original incandescent lights. I thought the sealed oval incandescent lights were burnt out because the signals and brakes wouldn't even light up.

At the trailer wiring connection a multimeter indicates there is 11.86V for the running lights but the signal and brake lights only have about 10.2V. Note, the trailer wiring connector is a T-style connector.

- Could the low voltage on signals/brakes be due to a weak flasher?
- Does the wiring harness need to be replaced? This trailer wiring harness used to work fine.

My presumption is the ground is OK because the running lights work on the trailer. Fuses have been checked and swapping relays made no difference.

Any insight is appreciated.

Thanks

 

Don't buy anything. Clean your connections. Those symptoms are classic for corroded or bad connections.

Steve

 

as above.

truck and trailer 7 pin... check for pinch damage to trailer cable to truck...
do not assume anything about a ground. you can not have to many ground points.

you problem is most likely BAD Ground, Damaged wires.. corrosion at connections.

if your 11.86 was with truck running.. another clue...
truck should be 13.6 or better... and trailer running lights should be 12.5 or more

I would go thru all of the grounds routes first..

I just replaced the 10 foot 7 pin cable from trailer to truck, and added a waterproof work box behind front frame of trailer.
.

 

The T-connector isn't helping either. Open the hood, and see if you have a relay box mounted aft and next to the fuse box on the driver side inner fender. If you have the relay box you can ditch the T connector wiring, and use the truck's factory trailer wiring. There should be one gray and one black, round, 4 pin connector hanging aft of the spare tire (one of the connectors only has 3 pins installed). Find an OE 7 pin harness from the dealer, or the junk yard, and it will plug right into those connectors. You can also cut the connectors off, and wire in an aftermarket 7 pin plug. I got the pigtails off a trashed 7 pin harness, and wired in an aftermarket plug; keeping the stock wiring connectors. This will take the load off of your headlight switch.

 

Another vote for connections and grounding.

LED lights hardly draw any amperes.