There is a short in the wiring on my trailer that keeps blowing fuses, so that tells me it's grounding somewhere. What are some ways I could troubleshoot to find where it's grounding at? I definitely don't want something that will give it as much power as it can handle and start a fire, so I'm almost thinking an electric fence charger that will send a pulse every 2(ish) seconds, and just use a multimeter to find how far back into the trailer the current is getting. What other ways would I be able to track down where the short is occurring?

Another caveat is that the short isn't blowing the fuse right away, so I'm assuming it's bare wire touching metal, but only if it gets bumped into the metal.

  • 3
    An electric fence charger is very, very, very high voltage. It will tend to cause insulation breakdown in the electrically weak insulation used on automotive wiring (which is optimized to resist vibration, oils, extremes of temperature). I'm not sure I would use it on house wiring either, same reason. Oct 21, 2018 at 19:06
  • I agree with Harper my fence chargers are 15000v even cheap ones run at 5000v but at night you may be able to see it arc if LED lamps do not try it would fry the low voltage junction in the LED's if standard lamps it may not have the wattage to blow the elements but you would be taking a chance on popping all the filaments.
    – Ed Beal
    Oct 22, 2018 at 13:23

3 Answers 3


You should have 12V being supplied to your trailer, Not 24 or 48. It won't start a fire but it may blow the 195 bulb in the marker lights.

I'm guessing You Have A Steel 2X3 Framed Trailer ? And not an aluminum I-Beam trailer or a small canoe trailer/water craft trailer with an open rail to test for current with an amp clamp

It's hard to say how test your trailer because there's so many different types of trailers ( sjv, sj, bj, ltv, lpb, pb, apb, sv, canoe, flat-bed, horse-trailer, etc ) the list goes on

But generally you have 4 amber lights on the front of the trailer, 2 tail lights and either a bar light of 3 separate red lights on the back. So another question I'm left asking is: are any of the lights dim, flickering, or are they just all off.

If it's all the lights that are off, Then It's your car, or the trailers main ground which should be on the bottom of the trailer near the tongue.

If it's just one side of your trailer then it's most likely your fender light which should have a quick connect, it may have fell out and bounces to the frame, each amber light has a separate ground aside from the main ground, That helps to determine the short in the trailer so all the lights don't go out at once while driving down the road

If you have a multimeter you can test from your ground to power where it connects to your vehicle, Then from ground to each signal wire for voltage (left blinker- yellow, right blinker- green, lights on black, Ground white, Brown is the railings ground) to make sure you aren't getting a short from the white ground wire or another one, You can even test one side on the trailer, For example: Left side, Yellow - Brown wires = Ohms of resistance and continuity and Right side: Green and Brown = The same ohms of resistance value and continuity,

If you set your multimeter on continuity you can put your red lead on the trailer and your black on the white wire on your trailer plug, if you get continuity your good

But it's always likely that you could have a pinched wire behind one of your amber lights

Then again, do you have electric brakes on your trailer or does it use fluid ;) you'll know because their will be an extra blue wire ( 5 prong )

  • Sorry, I should have added some detail about the trailer. It's a gooseneck horse trailer. Sounds like I should replace the fuse when it's dark and take a look at the amount of light to each light/side of the trailer? And for testing, if I have 2 multimeters, I would attach one to the plug and carry the other one around to the different running lights? I don't know how long it was before the fuse blew last time. I replaced it in the daytime and it was working, then traveled for a few hours before nightfall when it wasn't working. Oct 22, 2018 at 4:38
  • Yes to wait until it's dark or pull it into a garage/barn and check out the lights, and 2 multimeters won't for one reading, you should be able to test 95% of it from the plug with one multimeter
    – user38183
    Oct 22, 2018 at 6:07

I have a bunch of trailers: horse, boat, flatbed, and dump styles. The location I usually find a short is where the wire comes through the frame to a light. Many times after years of use the grommets that protect the wires fall out and the insulation rubs through the wires, my first check is at night to see if any of the lights are out, tall grass can pull a wire out then bouncing around it shorts and blows the fuse , on my boat rubbing through is more common I have replaced that wiring 3 times since the early 90's as the salt water and lots of use really accelerates the wear on the wires. For the horse trailer make sure to check your upper marker lights these can get water in them and hold it once the parts start rusting a short can blow the fuse I have seen this happen also.


I would start by replacing the fuse with a bulb: an 21W indicator bulb is usually sufficient. Mount it so you can see it when working on the trailer.

Then, in your case I would proceed as follows:

1) remove all the bulbs from the lights (test them as one, or more, can themselves be faulty), do not refit yet.

2) if the 21W bulb is "on" while the other bulbs are removed then the short is present, so start by gently moving the trailer cables where they go through clamps, holes etc. When you move it and the 21W bulb goes out, then you have, probably, found the location of the short. Take care, there may be more than one short.

3) if the 21W bulb is not "on", then moving the cables gently can cause it to come on...

Good luck and patience is required...

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