Right Tail light constantly lit

[azcummins]

Thought I'd throw this out before I went digging too deep into my trailer...



Noticed today that when I came home my Right tailight on my trailer was constantly illuminated. It is the higher voltage brake light/turn signal bulb. It stays lit even when the trailer and truck lights are turned off.



I do have a constant hot on the trailer as well as trailer brakes so I'm thinking the tail light is touching one of those two "constant hot" wires to make it constantly light up.



What do you guys think?

 

[stg2500]

It could be a bad ground wire. Bad grounds do funny things.

 

[Gary - K7GLD]

HMMmm - seems like if that was the case, BOTH rear lights would be lit, since I think they are on the same circuit... But bad ground wires make electricity look for seemingly strange ways to complete a circuit...

 

[azcummins]

Do you guys think the ground from the truck to trailer is bad or a ground wire somewhere in the trailer?

 

[Gary - K7GLD]

If that IS the problem (I've seen it happen!) it could be in the trailer itself, or between the truck and trailer. Quick way to check, is to run a temporary ground lead directly between the truck and trailer - making sure to use a good clean grounding point on both ends. If THAT doesn't change things, I'd use a meter to check continuity from the trailer's main ground wire inside the trailer plug directly to a good clean frame ground on the trailer itself - should be VERY close to zero ohms... If not, you have a poor or open ground connection somewhere in the system.

 

[redramnc]

Sounds like your constant hot is going to ground through the bulb. Since it is only the right side it is the right turn signal circuit providing the ground path. If it were the running light circuit all of them would stay lit. The bulb is a good thermistor so it will not give you a dead short and blow a fuse.



Depending on how your trailer pigtail is wired on the truck it may also keep the truck right side lamp on.



Look for a screw that may be able to rub the wires and short them together. Been there, done that on a small cargo trailer. Replaced a piece of paneling and then the running lights stopped working. Found a screw had punched a hole in the wiring to the top lights and was grounding out the circuit.



Good luck finding it.

 

[azcummins]

Got the light worked out. Turned out that the RT wire (green) had come out of the trailer light plug and was touching the hot post in the plug so it was constantly lit. Easy fix but I learned a lot of what to look for thanks to your responses. Thanks!

 

[Gary - K7GLD]

Interesting - *I* woulda thought that type of short would have backed up into the truck, and lit the truck turn signals as well... .



Learn somethin' new every day...

 

[redramnc]

Gary,

You are correct - but since the wire pulled out in the connector there was no path back to the truck side of the light circuit. That's why I mentioned that it should hold the truck light on depending on how the pigtail is wired. I kinda fudged that reply because I thought it strange that the truck side was not staying lit. Should have realized that the connector was part of the problem. When doing wiring diags the KISS principle is definitely needed.



Of course, when you have seen some of the butchered wiring jobs I have had to fix over the years there is a tendency to go looking for really goof ball causes for some of the problems. For a while a couple of years ago I kept getting bit by bad grounding circuits. Now all my grounds get a ring terminal, internal tooth washer, and a grinder down to bare metal - fool me once, shame on you, fool me twice, never

 

[Gary - K7GLD]

Seems like, when problems arise in setups like this, the first/best approach is to carefully inspect all the connectors/adapters that have been fabricated or modified out in the field... Several trailer/truck connectors I have had to trouble-shoot INVARIABLY will display SOME loose or failed connections - one common problem that is real scary, is those where the "electronics expert" has stripped the wires at least a half inch farther than needed - then after securing the wires, simply leave all that exposed wire to eventually meander over to get better acquainted with its neighbor...



And after a relatively short period of time and usage, you can COUNT on those plugs using the "insert-wire-then-tighten-screw" type connections to work loose due to movement of the cord over the road... I really prefer to solder my connections.