Trailer wiring recently done, now taillight is out and bulb replacement didn't fix it. Suggestions?

Question

Recently had a standard 4-way plug installed on my van for trailer lights. The plug worked properly for a couple times towing a trailer, but now I have a taillight out. The van is a 2012 Chevy Express 3500 (15 passenger van).

I ordered replacement bulb and installed it last night but that didn't fix the problem. Actually tried both the bulbs in the 2-pack, and the original bulb doesn't appear to have a broken filament.

The bulb is the style with 2 filaments in one bulb, where one of them lights up for the taillight, and the other lights up for brake light and turn signal. The brake light works properly, so its only the circuit for the taillight that's not working. Also its only the taillight on the driver's side - the passenger side works properly for both tail and brake light

I'm just looking for suggestions on what to check next. Do you think its possible something shorted out and blew the fuse? Or perhaps the shop that did the trailer wiring spliced into the taillight wire and that splice came loose or overheated or something?

I do plan to contact the shop that did the wiring, but if there's some simple fix I can do in a few minutes its easier than going back in.

Thanks for any tips.

Anonymous · Answer

Troubleshoot. Charge the battery. Get a 12V incandescent test light and learn how to use it. Check power and ground at the connector with the park lights on. The ground is shared on the bulb so it is very likely you have a power loss to the tail light. Trace your wiring upstream to the switch (or relay) and find the missing power.

Remember to have the park lights on every time when testing or you will get false results. Good luck.

Remember to have the park lights on every time when testing or you will get false results.  Good luck.

oklatom · Answer

Get out your voltmeter, set it for 15 DC volts, turn on the tail lights.  Check for voltage at the socket.  If not trace back until you find voltage.  When you do replace he bad connector.

CactiJoe · Answer

Main thing to look for is those "quick connect" inline wiring connectors. They are the type you squeeze with a pair of pliers and the little piece of metal cuts through the wire insulation to the copper wire to make contact. These quick connectors are often "crappy" connections and any water that gets in there or a bump in the road can open the connection. Meaning no juice flows through that tiny piece of metal to connect both wires in the connector. Best to solder the wires to the plug pigtail for a solid connection. Not too difficult and best in the long run.

? · Answer

I suspect the tech that installed the plug may not have connected the wires properly and something pulled loose. Just a guess.

Scott · Answer

No, something didn't short out and blow the fuse, or neither brake light would work. You need to check for voltage at the socket, then there should be a point where the taillight harness connectes to the main chassis harness. Check there for voltage.

Trailer wiring recently done, now taillight is out and bulb replacement didn't fix it. Suggestions?

5 Answers