Can't figure this one out

[Billieg]

This is crazy. The dr. side turn and brake signal doesn't work on the 5th. I have juice to the elec. box on the pin where the red wire from the truck will flash the tester but only if I disconnect the trailer red wire to the turn/brake lights. As soon as I connect the truck to the trailer wire the truck still flashes but the red wire from the truck or tail lights don't.

Now this seems to be a short BUT if I hook up a 12v source to the trailer red wire the brake/turn lights light up bright! So the wire isn't broken or shorted out.

Why would the lights light up bright with a jumper from the parking lights but not flash when hooked up to the truck?

Anyone?

[HHIDan]

Most crazy electrical problems with trailers have to do with a bad or missing ground. Check all your grounding near the light that does not work.

[Billieg]

All the grounds are good because the park lights work and if I hook up the turn/brake lights to the park lights they come on bright.

[HHIDan]

It's not a Short-circuit because you're not blowing a fuse so it has to be a floatting gnd, I think. When you plug in the other source I suspect the wires are shorter and that might be why it works. With long wires the chassis grounds are more important/critical. I had a similar problem when I wired "trailer lights" at the back of my Jeep. I had to gnd at the front of the Jeep and at the back also.

[HHIDan]

The socket itself may not be grounding properly.

[Billieg]

Well, thanks for replying. I just hooked up the right turn/brake wire from the pin box to the left turn/brake light and they work fine.... So, i suspect it may be my flasher isn't strong enough on the right side to power them. Pulled the flasher and tomorrow I'll get a new one.

[puttin]

If nothing suggested so far doesn't work, try looking at the tail light converter in the truck. Sometimes there's nothing to "fix" so you'll have to replace it. Did something "funny" happen just prior to this problem? Were you towing a boat and dunked the trailer without disconnecting the trailer plug? Were you towing something new and condition unknown, etc? Let me know what you find if your flasher doesn't work.

Thanks.

[Billieg]

Originally Posted by puttin

If nothing suggested so far doesn't work, try looking at the tail light converter in the truck. Sometimes there's nothing to "fix" so you'll have to replace it. Did something "funny" happen just prior to this problem? Were you towing a boat and dunked the trailer without disconnecting the trailer plug? Were you towing something new and condition unknown, etc? Let me know what you find if your flasher doesn't work.

Thanks.

Well I put in a new HD flasher and still the same thing. This is crazy. I get a turn signal on the input wire and when I hook it up to the left turn signal wire nothing.

I can take the right side wire for the turn signal and hook it up to the left one and the left side works perfect so it's not shorted out or a bad ground. The turn signal on the truck works fine.

[Et Cetera]

I have seen a bad bulb where the broken filament touched the unbroken filament act like this. All the bulbs work, so you have to look for one that is brighter, or just replace them with known good ones, one at a time.
Drove me NUTS the first time I saw it.
Good luck
etc.

[Roam America]

Originally Posted by Billieg

I can take the right side wire for the turn signal and hook it up to the left one and the left side works perfect so it's not shorted out or a bad ground. The turn signal on the truck works fine.

You say when you connect the right side wire to the left side trailer light, it works. have you tried connecting the left side wiring to the right side? Essentially truck left side to trailer right side and truck right side to the trailer left side. See if that works. Then you'll know for sure if the trouble is in the truck wiring or trailer wiring and which side.

[Shellback1]

Do you have diodes to convert the truck Light to the TT? Could be a bad diode or connection.

[puttin]

I think it would be worthwhile to check the converter in the truck or connect the trailer to another vehicles elect. system with the plug and see if it acts the same.

[HHIDan]

Ok, left is red and right is brown and left don't work.
If you connect brown to left then it works. If you connect red to right does that work? If you have a ohmeter, disconnect the trailer from the truck and measure the resistance between red and ground and compare it to brown (to ground also). Looks like left circuit would be "over-loading" the turn signal and that might be a bad bulb (as suggested above) If the two sides are the same resistance then the problem is on the truck side but you changed the flasher??? It's a good one...

[wingnut60]

Two sets of fuses on Fords? One on right side of dash, one under hood. Check the ones listed for trailer lights under the hood...
Joe