Trailer Light Problem

[trees132]

Hey Guys,

Have a question about an equipment trailer. One of the tail lights works with running lights but does not function for signal and brake functions. Any thoughts on how to troubleshoot this problem? I have a multimeter and can use it a bit.

Thanks!

 

[nikdfish]

Check for voltage on the appropriate wire (green for right yellow for left) while the brake is held or with a battery supplying power to it at the plug, checking at the point the wire enters the light. If power is found & the bulb tests ok then probably a bad socket or bad connection between wire at the point it conects to the light. I have seen a few "push in" connections go bad due to corrosion on wire or light fixture.

Nick

 

[tthopskin@yahoo.ca]

some cars trucks run with 2 different lights now and if you dont have the box .then you need 2 sets of lights on each side one for brake and stop one for turn ...this may be your problem

 

[Diamondpilot]

Should be a two element bulb. Sounds like a bad bulb would be my first guess.

Chris

 

[timswi]

Should be a two element bulb. Sounds like a bad bulb would be my first guess.

Chris

That would be my first check as well...

 

[Depmandog]

I would guess that over 50% of my trailer lighting problems have stemmed from a lack of a good ground back to the towing vehicles battery. Make sure the trailer is attached to the towing vehicle and your ball isn't rusted and it's properly lubed.

Not suggesting that's your problem..only that's my first order of business when I go to troubleshoot trailer wiring.

 

[aczlan]

That would be my first check as well...

Same here.

Aaron Z

 

[bcp]

And if you have a hitch receiver, the insert may not be making a good ground with the receiver due to rust or paint. I like to see a wiring ground on trailers.

Bruce

 

[BigE_]

After the ground check and the bulb check, I pull out the meter and make sure I'm getting signal at the bulb. If there, then I go back to the truck and make sure I have signal at the connector.

Lots of times it is the connector itself, especially the 7 pin connectors.

If no signal at the connector, check your fuses. In my truck I have a fuse for each light.

The last wiring problem I had was that both tail lights blinked at the same time when the right blinker was on, but only the left when the left blinker was on. Pulled apart both lights and even replaced some with LEDs. Drove me nuts until I checked at the connector. Same issue at the connector with the trailer disconnected. It turns out that my Silverado has a trailer wiring module. I pulled that out after taking apart the dash. $35 for a new one, so I tore that apart and found one relay had welded shut. Popped it open and good as new.

 

[WM75Guy]

I bought a 7 pin tester that doubles with a 4 pin adapter. It has saved me lots of time knowing the truck receptacle was working correctly.

 

[newbury]

I just went thru about 2 weeks of off-and-on debugging the same thing.

Standard procedure seems to be
First check for good bulbs
Check for ground with a continuity checker from bulb
Check your plugs for proper power etc. 7 pin plug on tow vehicle, how to test? - YouTube

I had to replace the 7 pin connector on the vehicle - one of the blades had broken off and would only make sporadic connection
My two rear clearance lights only got sporadic ground - I drilled the screw hole a bit and shoved in some copper from a Chore Boy and rescrewed - got good ground
And replaced the two front markers entirely.

 

[Xfaxman]

Hey Guys,

Have a question about an equipment trailer. One of the tail lights works with running lights but does not function for signal and brake functions. Any thoughts on how to troubleshoot this problem? I have a multimeter and can use it a bit.

Thanks!

Don't overlook the obvious, the signal and brake functions are a separate filament from the running light in the bulb. Check to see if it is burned out.

If the base of the bulb is copper and slightly corroded enough to not be grounded it will do that because the filaments are now in series, not in parallel to ground.

 

[jhasafety1]

When going through your system I like to add a ground from tow vehicle to trailer. I also add a ground wire to each light if I'm rewiring and when checking any splices I usually solder all connections and also check the bulbs. Hopefully its not something on the tow vehicle.

 

[Travelover]

When going through your system I like to add a ground from tow vehicle to trailer. I also add a ground wire to each light if I'm rewiring and when checking any splices I usually solder all connections and also check the bulbs. Hopefully its not something on the tow vehicle.

+1 Seems like a bad ground or corroded splices are the problem most of the time. I do the same with the grounds to each light and soldering splices routine.

 

[Soundguy]

I bought a 7 pin tester that doubles with a 4 pin adapter. It has saved me lots of time knowing the truck receptacle was working correctly.

i love those testers too. can leave it in and check wiring and connections in and under truck too.

 

[Soundguy]

I had to replace the 7 pin connector on the vehicle - one of the blades had broken off and would only make sporadic connection
.

bet that one was a hair puller!

 

[kenmac]

Do yourself a favor and purchase the LED trailer light kit for about 50-60 bucks. I did this and all my trailer light problems went away

 

[Soundguy]

any problem with older mechanical flashers ( thermal type? )

 

[aczlan]

any problem with older mechanical flashers ( thermal type? )

Not if they also control the truck turn signals. If they only control the trailer turn signals, you may need to switch to the newer electronic ones.

Aaron Z

 

[skylarkguy]

There is also the Universal Law of Functioning Trailer Lights...there are only a finite number of trailer lights that can operate in the the universe at one time. If you get yours back then someone else lost his. You might just have to wait a while.