Why won't the left hazard/turn signal work on my trailer?

[mamawildbear]

Looking for some advice from those of you experienced with these things.

We have a 2005 Ford F150 and a Springdale 260LE trailer.
Everything was working fine for 6 months. Today we hooked up and went to check the lights and the rear left light does not work properly.

Turn signal - none
Breaking - none
Hazard - a dim solid glow, no flash

All lights work fine on the tow vehicle whether trailer is hooked up or not.
We swapped bulbs from the left to the right on the trailer and the problem stays with the left side so not a bulb issue.

Per another thread I had purchased a heavy duty turn two pin flasher and we connected it directly to pins 3 and 4 of the trailer umbilical plug. All lights on the trailer work fine including both rear lights which flash as they should, so not an issue with trailer wiring or 7-way plug.

Now we're looking at the F150. But since the hazards and turn signals work fine on the truck, we are assuming all fuses are good. Everything worked fine before so we're assuming our flasher can support the extra lights on the trailer? But now it's not working so why?

Hubby has gone to buy a replacement 5 pin heavy duty flasher for the truck just to see if that makes a difference but otherwise we are baffled. Any ideas?

[mamawildbear]

AND... same issue with replacement flasher. Still baffled.

[JRTJH]

If you have the factory installed 7 pin umbilical, there is a plug on the back of it that is likely corroded. If you have a "owner installed" 7 pin umbilical, you may have corrosion in one of the splice connectors in the wiring.

Either way, check for corrosion and bad electrical connections. If your tail/brake/turn signals work on the truck and work from the umbilical back on the trailer, then the problem has to be in the wiring on the truck "from the splice/connector for the umbilical back to the umbilical".... All the rest has checked good.

[Larry1013]

To me, I would check to see if the trailer and truck had a good Ground (negative) connection between them.

Also, check underneath where the trailer wires connect to the truck wiring for problems.

2005 Owner's Manual link

http://www.fordservicecontent.com/Fo.../05f12og5e.pdf

[Hollywood 2979]

Also check the flat prongs on the trailer plug, clean them really good and also bend them in a little sometimes there is not enough pressure on older plugs to make good contact, just alittle bit, also a little dieletric grease work on keeping corrosion on plugs down.

[mamawildbear]

Hubby figured it out. It turns out that the F150 has a gajillion fuses with very specific purposes. The left trailer light fuse was dead. It is now replaced and working and we just hope there's not an underlying problem that made it pop in the first place. 5 hours and 5 auto parts store trips later and we are good.