HELP! I keep blowing the stop light fuse - Fiberglass RV


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Old 04-20-2018, 07:17 PM   #1
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Trailer: Scamp 16 Deluxe
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HELP! I keep blowing the stop light fuse

Hi Folks,

I could use some help figuring out a brake light fuse problem. I have a 2014 Scamp, 16' Deluxe with side dinette and the tow vehicle is a 2007 Toyota Highlander, with the tow package.

Briefly, the problem is that the stop light fuse in the Highlander randomly blows. Interestingly, the stop light fuse being blown turns on the VSC, ABS, and Brake warning light on the dash, and locks out the shifter from being able to put the car in gear. Replacing the subject 20 amp fuse corrects the problem for a while, but it continues to happen. The fuse blow seems to be associated with bringing the car to a stop, turning it off, and then starting it. That's when the fuse usually blows (but the first time it happened, I was rolling down the highway). An earlier attempt at repairing the problem (by my trusted auto mechanic) involved replacing the brake light switch at the brake pedal, along with the fuse.

Clearly, there is an intermittent short to ground somewhere. The car runs fine as long as the trailer isn't attached. I have used a meter to test the brake light circuits in the trailer, and there doesn't seem to be a hard short between the stop/turn light socket and ground. I've also cleaned up the socket and plug on the trailer pig tail and tow hitch (although now that I'm home, I'll do a more thorough job of that).

Has anybody run into this before with a Scamp? Any ideas on how to proceed with troubleshooting?

Thanks in advance! Let me know if I can answer any further questions.
Chuck
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Old 04-20-2018, 08:18 PM   #2
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Name: bob
Trailer: 1984 u-haul ct13; 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
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Do the lights on the trailer work? Did you check the bulbs on the trailer. I had the filaments in a stop / tail light break and short out one time causing the fuse to blow. As you have found, that fuse feeds more than just the stop lights. Check the contacts in the bulb sockets, pull the contacts out of the socket if you can to inspect them. Apparently an intermittent short so that makes it harder to find. Trace the trailer wiring as much as you can to look for where it may have rubbed through the insulation. Could be a loose wire or short in the trailer plug, easy to pull on the wire when disconnecting from the tow vehicle and possibly disturbing a connection in the plug.
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Old 04-20-2018, 11:06 PM   #3
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The lights on the trailer DO NOT work when the fuse is blown in the TV, otherwise they work fine. They are clean and corrosion-free.

Trailer plug is indeed suspect, and I'll check it tomorrow.

Thanks!
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Old 04-21-2018, 05:45 AM   #4
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Name: bob
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I understood that they didn't work with a blown fuse. I was questioning with a good fuse to determine if there was a bad bulb. So bulb is ruled out, plug next, work back from there.
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Old 04-21-2018, 06:11 AM   #5
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Missouri
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my opinion

yes I would tear into the plug just one little wire touching ground can cause this. you will need to look at both plugs by the way to make sure everything is good.

good luck

bob
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Old 04-21-2018, 06:31 AM   #6
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Do you have Toyota's OEM trailer harness, or is it an aftermarket harness and light converter box?
If you have an aftermarket converter, unless it is a powered converter module (has it's own 12V feed so trailer lights don't draw power from the HL lights circuits) I'm just guessing here but I would think you're running fairly close to the HL's 20 amp fuse rating. The HL's stop lights consists of four 7443 bulbs, 25 watts each. The center 3rd brake light uses a 921 bulb, 18 watts.
You trailer probably uses two 1157 bulbs, 27 watts each.
That's a total of 172 watts, that's about 14 amps.
And as you found out, the same circuit also feeds (or at least sends a signal) to the VSC, ABS, and shifter lock solenoid and what not.
If you're close to the fuse's 20A rating, the fuse doesn't blow but certainly heats up, and after repeated heat/cold cycles, it weakens and eventually burns.
It's either that or you have an intermittent hard fault as mentioned, which could be hard to find.

In any case, if you have a non-powered aftermarket converter box, I suggest you get one. If you have a short in the trailer's wiring somewhere, it won't screw up the tow vehicle's electrical and blow an important fuse. Losing ABS/VSC/TRAC and the ability to get out of park is a significant nuisance IMO.

Carl
(2006 Highlander, same vehicle as yours)
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Old 04-21-2018, 06:34 AM   #7
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Name: bob
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sooo right

yes carl you are correct I was looking around and found a fuse block my mechanic had no idea about.

I have a 2015 ford edge I do not understand why ford thinks these blocks must be hidden out of sight.

blow one of those fuses and its going to be a long day for most!

bob
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Old 04-21-2018, 07:13 AM   #8
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+1 to Carl's question. Determine which loads are on that circuit. Trailer power drains while towing:

- trailer running lights, if incandescent, add up to several amps (and more while stopping)
- if your camper has electric brakes and if they are on that circuit, that adds another 6 to 8 amp load per axle while you are stopping
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Old 04-21-2018, 07:56 AM   #9
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I don't think the marker lights are on the same fuse as the stop lights, and the brake controller usually has it's own line directly from the battery to power the magnets, the tow vehicle's brake wire is just a signal to activate the brakes. Still, some more draw.
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Old 04-21-2018, 08:08 AM   #10
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Finding intermittent wiring problems can be tough. One method that can sometimes be useful is to wire a test lamp in place of the fuse. No short - the light will be off (or very dim). Start wiggling the wiring, and watch for the lamp to go to full brightness. Much cheaper than replacing a fuse each time it blows...
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Old 04-21-2018, 09:06 PM   #11
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Trailer: Scamp 16 Deluxe
Washington
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Carl, I think what I have is an aftermarket brake light controller. The car supposedly had the Toyota "tow package" wiring harness, but in looking under the back end, I see some flat 4-pin connectors and a few other wires all going to the socket on the hitch. I did pay to have that installed a few years ago (not at Toyota). I'll see if I can tell if there is independent power going to the brake light controller - but I don't think so.

I'm about to order a new pig tail and plug for the trailer side, and I'm shopping for a waterproof junction box to install it. I think that will clean up the trailer side pretty well. Everything else is buried under insulation inside the trailer and it's hard to imagine a wire frayed or something under there. The tail lights look pretty good as well, but I think I'll also buy some LED bulbs for the tail lights and get those installed. If nothing else, that will help reduce the draw on the brake light circuit.

Meanwhile I'm going to dig around under the back of the car to answer your question for sure, and to be sure nothing is corroded or frayed under there.

Would you suggest taking the car to Toyota to be sure the proper harness and controller are installed or to get them installed?

Thanks for your help!

Chuck
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Old 04-21-2018, 09:30 PM   #12
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Quote:
Originally Posted by beardrum View Post
Would you suggest taking the car to Toyota to be sure the proper harness and controller are installed or to get them installed?
I'm sure the Toyota harness - if still available - would work just fine. However you might have to renew your house mortgage or sell one or your kidneys to pay for it, as it is stupidly expensive.
I have an aftermarket powered converter and it works just fine.

Toyota's harness plugs in a large connector at the rear left of the vehicle, buried under plastic trims and covers. All the lights and turn signals wires are in this connector, including the wire that feeds the light converter itself, which gets its power from the fuse labeled "Towing" (or similar, can't remember exactly) in the engine compartment fuse box. When you buy the towing package at the dealer, they plug in the harness/light converter and put a fuse in the socket to power it. I wired my aftermarket converter module to use this same wire as a power source, just like Toyota's.

Switching to LEDs is a good idea, that should reduce the load quite a bit.
If the fuse only blows when the trailer is plugged in, and if the cause is an intermittent short somewhere, chances are it's on the trailer side somewhere. Replacing the trailer pigtail isn't a bad idea, but I would install LEDs first anyway and give it a try, even if the problem persists it remains a good upgrade to your trailer.
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Old 04-22-2018, 06:45 AM   #13
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sort of off topic maybe not

I had 90 cadilac that developed a miss I mean big-time took it to my local mechanic I trusted former gm guy. he worked on it and worked on it all the time charging me labor but couldn't get figured out.

the next I heard he had sent it to another mechanic friend who went the same route but one day for some reason he was standing outside the car cranking the motor and saw fire coming off the block.

so now he finds someone to crank the motor while he is under the car. guess what? as I had told him check for ground with the al. motor the ground bolt had worked loose thus creating a bad ground!

he tightend it back up no more miss I was out the car for 2 weeks and a 1k bill! 12v can be crazy sometimes.

I have to believe you are catching a ground short somewhere for that to suddenly blow a fuse but who knows right now!

bob
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Old 04-22-2018, 07:30 PM   #14
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Name: Chuck
Trailer: Scamp 16 Deluxe
Washington
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It does NOT look to me as if the brake light controller gets power from anything other than the light circuits. There is a capped off red wire in the same compartment as the brake controller, I suspect that is power. I found the big white connector that Carl spoke of. There does not seem to be anything corroded or frayed under the car (other than the seven pin connector socket itself, which I'm in the process of cleaning up.)

Carl, can you recommend a brand/model of brake circuit converter? Per your suggestion, I'll replace the small Hopkins controller with something that is powered.

Interestingly, I find there is a fuse in the "tow" fuse socket under the hood, although it is a 10 amp fuse, and the owner's manual says it should be 20 amp. What's more, the print style on that particular fuse is different than all the others. I'm beginning to think this isn't the first time this has been messed with.

Thanks!~

Chuck
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