Author Topic: Trailer lights not working  (Read 2685 times)

Offline m_fumich

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Trailer lights not working
« on: December 30, 2019, 06:19:19 PM »
We have a 2003 Subaru Outback with dealer installed towing package and the 4 wire trailer light connector. When I bought a small trailer recently and the lights didn’t work, I wasn’t sure if it was the trailer or the car causing the problems. I bought one of these testers.



Turned the headlights on and the emergency flashers then plugged in the tester. No lights on the tester. The wiring harness led back to some kind of sealed box in the spare tire well with the Subaru label on it. I disconnected the harness and plugged the tester into the box. No lights. The wiring ran from the box and under the interior trim.

My wife had to go run some errands so I couldn’t do any further testing. Is that wiring on a dedicated circuit or is it on the same fuse as the rest of the tail lights?


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Offline m_fumich

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Re: Trailer lights not working
« Reply #1 on: December 31, 2019, 12:24:41 PM »
Finally had the chance to check the manual. There is a dedicated fuse for the trailer lights. It’s one of those TINY fuses. My fingers are too fat to extract the fuse. I’m not at the house so I can’t grab the pliers. I’ll find something to get it out.


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Offline m_fumich

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Trailer lights not working
« Reply #2 on: January 02, 2020, 09:25:09 PM »


I have no fuses like this. I’ll update once it’s replaced.

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« Last Edit: January 02, 2020, 09:26:50 PM by m_fumich »

Offline pep

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Re: Trailer lights not working
« Reply #3 on: January 03, 2020, 08:48:35 AM »
Lets think this thru,
1 assuming the fuse was good and blew when the trailer was hooked up
2 two ways to troubleshoot it
3 meter....... best quickest practic
4 fuses ..... can work but pain in the ass, and even when the short has been isolated, still need to trace the wire.

 If meter
1 remove trailer brake & tag light bulbs
2 black lead, to trailer frame
3 with red lead, at the connector
4 probe each pin
5 expected readings if the circuit is good, no shorts. 
6 open/no reading good..... no shorts

The trailer plug has 4 circuits.
1 ground most use the ball for that, and most times trailer lights do not work or are intermittent, because of the crud that accumulates on it
2 brake light circuit, one wire out to both L&R side, daisy chained, or serial, (same)
3 turn signal L&R each has its own circuit.


Read the trailer connector, one of the circuits will read continuity when rung out. That one will be the problem, shorted,
 Actually 2 will, IF the ground pin in the plug is connected to the trailer frame......... my money says that it will not be

happy hunting, easily  solved.

pep
1776 ................... what happened!

Offline m_fumich

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Re: Trailer lights not working
« Reply #4 on: January 03, 2020, 09:11:13 AM »
This has been low priority for me but I’m gradually making progress. I have a DVOM but my time has been needed elsewhere.

As you pointed out, replacing the fuse won’t necessarily fix the problem. What caused it to blow in the first place? I’m going to try the easy way first. I’ll replace the fuse and see if it blows again. If it doesn’t, great. If it dies, then I’ll troubleshoot more. All I will have lost is one fuse.


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