Here's a head scracther

[CancerKiller]

thank you all very very much. Greatly appreciate the help,

[Fins]

Trailer is old enough that I'd rewire the whole thing. After a while, the insulation on a wire in some hidden spot will wear off and expose the bare wire. This causes blown fuses. It's not a complicated job to rewire a trailer if u have some mechanical ability.
20200513_165159.jpg

[Bill Reynolds]

Mine goes
white
brown
brown
yellow
green

will open up the swing tongue and check in there. Didn't have time to do that today. Will keep digging.

The way I read this, you have a 4 pin connector with two brown wires exiting from one of the pins on the trailer side. Is this correct?
If so, you do not have trailer brakes. The 5th pin in a 5 pin connector supplies power for backup lights and is used to power the reverse solenoid if Hydraulic surge brakes are Present.
What is confusing me is how you are powering the fifth pin if you only have a 4 pin connector.
Could you post a pic of your trailer connector connected to your vehicle connector?

[lmoore]

Head scratcher is right. With a 4 pin connection, putting the truck in reverse shouldn't change anything since you don't have a specific reverse light/backup circuit. Nothing should happen, but if you want to confirm I would put a volt tester on the truck side of the connection and test all of them key on (no engine running) in Park and then in Reverse and see if you have a change anywhere. You shouldn't, but it would only take about 8 seconds to check and it would confirm that reverse isn't actually the problem.

[CancerKiller]

The way I read this, you have a 4 pin connector with two brown wires exiting from one of the pins on the trailer side. Is this correct?
If so, you do not have trailer brakes. The 5th pin in a 5 pin connector supplies power for backup lights and is used to power the reverse solenoid if Hydraulic surge brakes are Present.
What is confusing me is how you are powering the fifth pin if you only have a 4 pin connector.
Could you post a pic of your trailer connector connected to your vehicle connector?

Yes, correct, 4 pin, no red wire. No 5th pin.

[CancerKiller]

Head scratcher is right. With a 4 pin connection, putting the truck in reverse shouldn't change anything since you don't have a specific reverse light/backup circuit. Nothing should happen, but if you want to confirm I would put a volt tester on the truck side of the connection and test all of them key on (no engine running) in Park and then in Reverse and see if you have a change anywhere. You shouldn't, but it would only take about 8 seconds to check and it would confirm that reverse isn't actually the problem.

then I am lost. It is putting it into reverse that does it. Something has changed. Ran this setup for 10 months before it all started happening last weekend. Twice in reverse and now 2 broken brake switches. And it is somehow tied to trailer, truck runs fine without trailer. Reverse no problem. But put it in reverse with trailer and this thing is popping.

[bpicinc]

Ok. Single axle, no blue wire, I have white (ground), 2 browns, a yellow/brown and a green/brown. Which one am I tracking?

Brown wires are running lights, yellow/brown and green/brown are brake/turn signal.

[lmoore]

then I am lost. It is putting it into reverse that does it. Something has changed. Ran this setup for 10 months before it all started happening last weekend. Twice in reverse and now 2 broken brake switches. And it is somehow tied to trailer, truck runs fine without trailer. Reverse no problem. But put it in reverse with trailer and this thing is popping.

If you're positive it's related to reverse you should see something running the simple test I mentioned. The only other possible explanation I can think of is if there is a bare spot on a wire somewhere that gets moved when backing up, but with no brakes the only thing that should be moving in reverse is the tires so unless you have a wire running near the wheel/hub area I don't know what to tell you there.

[Islands]

Exactly which fuse is blowing?

[Fins]

See the pic in post #22. Examine every inch of the wiring on your trailer for that.

[billnorman1]

Just thunk of something. He has no reverse circuit on the trailer. Does he have a 4 wire or a 5 wire flat connector? If he has neither, somewhere in the round connector the reverse wire is contacting the ground wire.
On a flat connector 4 pin there is no reverse wire, in a 5 pin it is the farthest wire from ground.

[CancerKiller]

See the pic in post #22. Examine every inch of the wiring on your trailer for that.

yes sir, that's what I will be doing.

[DaveBrabec]

I had a trailer that would blow fuse in truck when backing into water and ended up being trailer bar light under outboard would get wet and fuse would pop. replaced light and still happened. Had to disconnect light.

[mastergun]

I had a trailer that would blow fuse in truck when backing into water and ended up being trailer bar light under outboard would get wet and fuse would pop. replaced light and still happened. Had to disconnect light.

I always disconnect my trailer cable before backing into water.

[CancerKiller]

I always disconnect my trailer cable before backing into water.

I sure will be for now until I get this figured out. Going to have to replace the brake light switch and get back to working properly today then find my exposed wire.

[CancerKiller]

Is there any way a battery or alternator starting to going bad could cause this?

[billnorman1]

HOW MANY PINS on your flat connector?

[CancerKiller]

I have 4 pins

[billnorman1]

Then your trailer cannot be the source of your short. If you have a round connector going to your truck, it is probably be the issue. With a 4 pin connector the back up circuit does not exist. On a 5 pin connector it is the furthest wire from ground physically.

[CancerKiller]

Well then this is truly weird. it happened twice now and only when in reverse. When trailer not hooked up, it doesn't happen.