Trailer Wiring

[Martin Perry]

Hi group,

I am designing a wiring loom for a trailer designed for transporting
cars. It uses a standard trailer chassis with a fibreglass body that
completely covers the car. All of the lights are of the LED type and
are mounted on the fibreglass body.

My question is, should I earth the trailer chassis from the earth in
the wiring loom even though it is not required as an earth return for
the lights? Are there any argument for or against?

Regards, Martin Perry

 

[Tim Shoppa]

Hi group,

I am designing a wiring loom for a trailer designed for transporting
cars. It uses a standard trailer chassis with a fibreglass body that
completely covers the car. All of the lights are of the LED type and
are mounted on the fibreglass body.

My question is, should I earth the trailer chassis from the earth in
the wiring loom even though it is not required as an earth return for
the lights? Are there any argument for or against?

The gotcha is that if you provide a wire for ground return, it must
be able to handle a simultaneous short on all the light wires. You
have to add up the fuse capacities for the brake, turn signals, running
lights, backup, etc. lights and be sure that the ground return is
sized to handle that much current.

If you are designing the whole thing from scratch, the best thing to
do is to provide a separate return wire for each light wire, and
ground them all to a single point in the towing vehicle. The way most
trailer lights are set up, with a ground through the chassis mount
only, this may not be possible. But most of the industry-standard
truck LED lights provide a way of adding a ground wire.

I *hope* that your LED lights are the industry-standard truck LED
assemblies. Getting testing and approval for homegrown light assemblies
is a pain in the rear.

I think it's a good idea to have such a ground, because otherwise you
are depending on the hitch ball contact for all light functionality.

Tim.