More Trailer Wiring Help

So my boat trailer lights work great. Only problem is when I put the trailer in the water, a fuse blows in my truck. Replace the fuse and back in business. Only problem now is I have a new truck and don’t have a clue if a fuse will pop, and if so, finding the damn thing.

I’m not any electrical wizard, but does that sound like a grounding problem? If so, is there a way to verify ground? My wiring runs inside the trailer’s frame so it’s hard to see much. I’ve tried pulling off some of the brake lights to check connections, but they must be caulked in and won’t budge and I’m afraid if I pull too hard I’ll start breaking lights.

Considered a rewire, but I have the same problem of potentially breaking lights, then trying to find replacements that fit correctly.

I would unplug and try it.
that way you will know if the trailer or truck

Unplug what?

I always unplug the lights before the trailer goes into the water. If it’s dark just do it right at the water’s edge.

I don’t think I have unplugged trailer lights in 20 years and it hasn’t caused any issues. You might have had a mouse nibble at a wire and it grounds out on the trailer frame when backing it into the water. I only unplugged the light because I would blow bulbs when the trailer hit the water, they must have changed the enclosures as I haven’t blown up a bulb in years

I agree with the others in terms of unplugging the lights before you back in can save a lot of issues. Electricity and water just don’t mix no matter how well your system is wired, it’s just easier on everything if you don’t put live electronics under water.

Your problem sounds more like a short than a grounding issue. My first guess would e that when backing in, the water entering the channels of your trailer is moving the wiring harness and a bad connection or chaffed spot on the wires is causing a short and blowing the fuse.

To some extent, you might be able to isolate which wire the short is on if your vehicle has separate fuses for trailer marker lights vs trailer brake lights. My last few vehicles have had the trailer lights on different circuits.

But that only helps a little in finding the potential fault. Especially when the wire is difficult to access for inspection and testing. I can generally find an open, but intermittent shorts can be difficult. Also, if the wire is old enough to have developed one short, what are the chances there are/will soon be more?

Usually I end up doing a total rewire. It takes 2-3 hours if you haven’t done it before, but it’s worth learning IMO because the need never goes away.

Grouse

Blowing fuses is not a grounding issue it’s a short issue. There could be a bare wire or your lights are shorting to ground when they are submerged. You can unplug your lights when you enter the water as others have said or you could replace your lights with sealed ones and possible some new wiring.

Thanks guys. I think I’ll try to remember to unplug when backing in for now, but it seems like a short term fix. Good thought on trying to isolate the fuse and what light function it’s linked to.

Unplug your trailer before backing in the water. Plug back in before going down the road.

There’s a threshold for troubleshooting vs. rewiring. I hate to put much time into troubleshooting when I can rewire in a couple hours.

Ralph Wiggum wrote:

There’s a threshold for troubleshooting vs. rewiring. I hate to put much time into troubleshooting when I can rewire in a couple hours.

Totally agree. ESPECIALLY with wire that’s run inside of the channels. Or if you see any signs of the use of wire nuts or SatanLok–errr, I mean “ScotchLok” connectors.

I had borrowed a friend’s bobcat trailer and the running lights weren’t working so I thought I’d try to fix them. I scooted underneath to have a look and my 9-year-old son did as well because he loves working on stuff.

“What are we looking for dad?”

“There’s a broken wire here. Look for a wire that looks smashed or stripped or cut.”

Tommy has keen eyesight and laying underneath a dark trailer he points 5 feet away toward the back and says, “There it is.” There was one broken wire in the 4-wire harness and he spotted it from 5 feet away. I think I’ll work with him on the next job too…

But that is much harder when the wire is hidden away.

robby wrote:

Unplug your trailer before backing in the water. Plug back in before going down the road.

If you have surge brakes you can’t always unplug your trailer lights because of the bypass solenoid powered by the 5th pin.

Pat k surge brakes work from the surge of the trailer acting like a brake pedal as your trailer surges forward I believe? You must be thinking electric?

The SCRATCHER wrote:

Pat k surge brakes work from the surge of the trailer acting like a brake pedal as your trailer surges forward I believe?

Right, but when you back up, that puts pressure on the actuator, which activates the brakes. Usually, there is a bypass that is hooked to the wiring harness so when you put it in reverse, the tow vehicle backup lights also power the brake bypass so you can back up without the trailer braking.

Ralph Wiggum wrote:

<div class=”d4p-bbt-quote-title”>The SCRATCHER wrote:</div>
Pat k surge brakes work from the surge of the trailer acting like a brake pedal as your trailer surges forward I believe?

Right, but when you back up, that puts pressure on the actuator, which activates the brakes. Usually, there is a bypass that is hooked to the wiring harness so when you put it in reverse, the tow vehicle backup lights also power the brake bypass so you can back up without the trailer braking.

I don’t have such a bypass with my surge brakes, thus I can’t back up going up hill unless I put the blocking key in on the tongue. Down a ramp is fine as the weight of the trailer pulls the tongue section apart.

walleyevision wrote:

I don’t have such a bypass with my surge brakes, thus I can’t back up going up hill unless I put the blocking key in on the tongue. Down a ramp is fine as the weight of the trailer pulls the tongue section apart.

Most of the ramps I use have the concrete “planks” with small gaps between them. That causes enough resistance that my brakes will engage if I unplug my trailer harness. I don’t have a blocking key for my surge brakes.

Pat K wrote:

<div class=”d4p-bbt-quote-title”>walleyevision wrote:</div>
I don’t have such a bypass with my surge brakes, thus I can’t back up going up hill unless I put the blocking key in on the tongue. Down a ramp is fine as the weight of the trailer pulls the tongue section apart.

Most of the ramps I use have the concrete “planks” with small gaps between them. That causes enough resistance that my brakes will engage if I unplug my trailer harness. I don’t have a blocking key for my surge brakes.

If you think you have a decent ground path “thru the ball”, pull the 5-flat apart and just plug-in the blue to blue circuit. This way, the lockout solenoid gets activated, yet the trailer lights are not powered.

HRG

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Hot Runr Guy wrote:

If you think you have a decent ground path “thru the ball”, pull the 5-flat apart and just plug-in the blue to blue circuit. This way, the lockout solenoid gets activated, yet the trailer lights are not powered.

Might be a “work around” for a five wire flat plug, however the guys I know who have surge brakes, are using the round RV style plug which is quite common factory installed on a lot of vehicles.

A re wire and sealed LED lighting will fix your problem and save you years of headaches. I did a trailer fix for a IDOer and and this what I found.

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bigcrappie wrote:

I did a trailer fix for a IDOer and and this what I found.

That was definitely Grouse’s trailer!

Ralph Wiggum wrote:

<div class=”d4p-bbt-quote-title”>bigcrappie wrote:</div>
I did a trailer fix for a IDOer and and this what I found.

That was definitely Grouse’s trailer!

Hey! How the heck was I supposed to know you can’t use wire nuts on trailer wiring?

Next you’ll be telling me the scotch lock connectors aren’t any good as well.