Trailer light puzzler

[$ sink]

Ok, workin on the taillights for the M416. took the military lights apart, ran new wire to them, installed a flat 4 wire harness and installed a new plug in harness on the back of the Dakota.

there are two 1155 taillight bulbs per side, one 1156 brake/blinker bulb.

Plugged it in and... taillights come on like they should.
blinkers work like they should... but

when the taillights are on and a blinker is on, the taillights dim as the blinker light bulb comes on. it is bad enough that with the blinker on one side, the taillight on the other side is blinking so bad it is hard to tell which is supposed to blink.

I ran a dedicated ground to each light frame inside the light, the two taillight bulbs are spliced together inside each light. there are no bare wires touching any metal anywhere.

and if I remove one taillight bulb from each side, it makes no difference in the way they act.

Help

[$ sink]

with the trailer plugged into the truck, the taillights on and a blinker on, you can see the other taillight on the truck slightly dimming. anyone know if this is caused by an overloaded flasher? do vehicles still have flashers? can you still buy heavy duty ones???

[Ppilotmike]

Did you run a ground wire between the truck and the trailer? From your discription it can only be a ground problem as that is the only thing common between the tail and turn lights.

[$ sink]

there is a ground wire in the flat 4 connector harnes from the truck. it is attached to a ground in the harness on the trailer that runs to the frame of each of the lights so it should be grounded well to the truck.

[Zoomer]

Mike might be suggesting that the ground in the 4 wire flat connector on your truck isn't grounded well to your truck frame. The military lights do not ground to the trailer frame and totally rely on the wire harness, thus your only ground path is through your trailer harness, the flat connector, and through your truck harness to your truck frame ground. Most trailers use the frame as a ground and will often work even without the ground in the flat connector. Don't rely on a wire connected to the light housing as a ground as I think it is isolated from the actual bulb ground (but I think you already knew that).

[$ sink]

Hey Mark. thanks, going out to try solid grounding both together.

the harness that hooks up to the truck has a plug that fits into the harness on each side of the truck. it appears to take a ground and blinker from one side and the tail and other blinker from the other side. I may be wrong, but the blue wire in it reads 0 resistance to the frame of the truck. :?

[$ sink]

yup, bad ground.

went out and put a set of jumper cables between truck frame and trailer frame and all is well.

guess I will be adding a ground tomorrow:roll:

thanks guys

[jpflat2a]

{pushing big red button}

"that was easy"
bad grounds, they cause a lot of problems