Trailer Grounding Question

[MNAirHead]

Dumb question..

Why do harnesses have a short lead (white) to ground the 4 wire loom to the trailer?

1-Doesn't it make more sense to run the white wire to both lights?
2-Why do lights work when the white wire is clipped?

[david58]

Why do harnesses have a short lead (white) to ground the 4 wire loom to the trailer?

That is a good question. The only reason I can think of is because they want you to use the trailer itself as a ground, which works to some extent. Take a boat trailer that gets backed into the water it gets corroded and rusts then the trailer loses it's ground.

1-Doesn't it make more sense to run the white wire to both lights?

Yes it makes a lot more sense to run grounds to both the lights.

2-Why do lights work when the white wire is clipped?

Because the ground is the trailer ball, which can work intermittently.

[MNAirHead]

I"ve had lights worked when the ball was not connected.

[Ol'fogasaurus]

I grease the ball and it does not transmit the ground well.

[Tom in PA]

The lights will work with the ground and trailer disconnected to a degree. I believe they basically carry the signal back the turn signal wire (or parking light wire for brakes/turn signals). It causes them to do some funky things and they don't work correctly.

Tom in PA

[2088 bob]

Relying on the trailer chassis to provide a ground has its good and bad points

Good point is that it is easy, bad point is that it is not always the best connection

iI always take the time to run my grounds to all the lights it provides for more consistant operation