Grounding a Trailer

pennwalk · Feb 25, 2006

Especially on older vehicles and trailers getting a good frame ground can be a pain then when it sits out behind the barn you are liable to have to do it all over. Trailers are a pain. /forums/images/graemlins/crazy.gif The last time I went to hook up my trailer the lights didn't work and it gave me fits. I ended up using a different vehicle and later on I discovered that the converter box for the trailer lights wasn't getting good ground. /forums/images/graemlins/frown.gif Another couple of perfectly good hours wasted. /forums/images/graemlins/frown.gif

Chris

755inNY · Feb 25, 2006

Especially on older vehicles and trailers getting a good frame ground can be a pain then when it sits out behind the barn you are liable to have to do it all over. Trailers are a pain. 

I would gladly pay an extra $50 for a trailer if it offered a separate ground wire to every light (including marker lights) instead of relying on the mounting screws to make ground to the frame. What a time consuming pain in the rear to chase down bad ground connections.

Jeff

BGL990 · Feb 26, 2006

I absolutely agree. Whenever I have to replace trailer lights, I always look for ones with separate ground wires. Even well prepared screw-into-frame ground connections will go bad over time as the screws rust.

Once or twice, where there was no separate ground wire run back to the lights, I've welded stainless steel machine screws to the frame and used those as grounding studs with wires to the lights.

century3045 · Feb 28, 2006

I try to use self tapping screws when attaching lights to trailers. It seems they dig into the metal a bit better, even if I have to drill a pilot hole to get it started. If I do use a bolt I will use one of the washers that cut into the metal.
An old lawnmower or motorcycle battery works good for testing wires also, its light and can be used where theres no electricity.
I ran into a problem once with the tee conector harness that fits between the taillight harness on the rear of the truck. Apparently the ground wire was just bad and it was causing all kind of problems on the trailer end, such as left turn would blink on L and R , running lights would cause turn indicator in truck to come on, and such. I was just about to pull the steering wheel and replace the turn signal switch and then decided first to replace the tee connector with a new one, good thing I did. Although the turn signal switch can cause these same problems, unhooking the trailer from vehicle made the problems go away, this convinced me it wasn't in the turn signal switch.

FarmDiesel · Feb 28, 2006

Just a note...before you connect the white wire in a 4 wire flat plug on your tow vehicle to ground on the trailer, take a 12V test lamp and check the wire for any power with the tow vehicle in reverse.

Some vehicles are wired with that 4th wire as the reverse wire. For example, I know that if you get an aftermarket converter to add a 4pin flat plug to a 95 F-150, the white wire is reverse. Ask me how I know that one...

JeffRey30747 · Mar 1, 2006

If you travel the interstate at night, it is easy to spot the guy who is using the hitch for the trailer ground. His trailer running lights are flickering brighter and dimmer as the trailer bounces down the road. /forums/images/graemlins/wink.gif
Whenever you wire a trailer or vehicle, save yourself some trouble later and terminate the ground wire properly on both sides.

Jeff

LBrown59 · Mar 21, 2006

An old lawnmower or motorcycle battery works good for testing wires
Something I use when trouble shooting trailer wiring is a battery charger
===== 
Something I've used for testing automotive wireing and lights both on and off a vehicle is a model train transformer.
I have 2 of them That I've been using for that for the past 48 years.

RobertN · Mar 22, 2006

There are some good answers here already. I just thought I would pass on a web page that has very good info on trailer wiring, and covers the common connector types. I have found the information very helpful.

Marks RV

There's info on 7-wire RV, 4 pin flat, 6-wire round horse trailer, and brake controller info.