Trailer Wiring Issue

I'd be looking at the ground wire on the left side.

Nope, bad ground on that bulb. What you think is the left turn signal working is actually the running light filament. The power comes to the positive side of the turn/brake light, but the ground is not there, so it exits out the running light filament.

You can prove this by looking at the actual lightbulb with the red lens cover off. The heavy filaments are the brake/turn, and the thinner filament is the running light.

Clean up the ground by using emery on the sides of the bulb socket and the bulb itself, and see if this helps. Sometimes it is actually the connection to the socket itself.

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Artum Snowbird wrote:
Nope, bad ground on that bulb. What you think is the left turn signal working is actually the running light filament. The power comes to the positive side of the turn/brake light, but the ground is not there, so it exits out the running light filament.

You can prove this by looking at the actual lightbulb with the red lens cover off. The heavy filaments are the brake/turn, and the thinner filament is the running light.

Clean up the ground by using emery on the sides of the bulb socket and the bulb itself, and see if this helps. Sometimes it is actually the connection to the socket itself.

I took the cover off and I can see both lights on and flashing but the turn signal very faint. It is a new bulb, cleaned up the connections on bulb and socket, but still does it. I am going to go buy bulbs I guess and see.

You are right, go buy a couple bulbs, you should have spares anyway, but that is not the problem. The problem is in the ground (neg) wire, maybe a bad socket....neg side !

You are on the right track now. As I said, the power comes in the positive side of the turn filament, but lights the running filament. Take a piece of wire to a ground, and connect it to the bulb socket to prove your bad ground on that socket. The connection to the socket is the problem spot.

It is not the bulb. Artum Snowbird described the problem perfectly. You have lost the ground connection on the left side. As Mike said, it can be corrosion on the socket but you have already cleaned that so that's probably not where the problem is. I believe most lights on RVs have a wired ground and there can be corrosion where the ground wire is connected to the socket. This would be very hard to see unless the socket was pretty rusted in that area. Also, the ground wire for this socket may be connected to the ground wires from the other lights on the rear of the RV and most connections are made with wire nuts (definitely a bad idea on something which get shaken as much as an RV does) and these can come loose. Note that when you have the running lights on you do not have a brake light on the left because the turn and brake are the same filament. Something you could try is remove the light assembly so you can get at the point where the ground wire is attached, have someone step on the brakes, and try to bridge the ground wire connection to the socket with a screw driver. If that's where the problem is, you might be able to make the ground connection and the filaments will light to full brightness. A replacement socket would be the easiest way to fix that problem. Otherwise it's in the wiring and it gets a whole lot harder to find. Sorry this is so long but I hope some of the detail helps. These kinds of problems can be very frustrating to fix. BTDT.

Ken

Thanks guys. It really turned out to be a connection in the socket as was mentioned. I cleaned it up as best I could and put a new bulb in and it works fine now.