Can somebody give me some advice on how to find an electrical short in my trailer?

I have a problem when I am pulling my boat trailer...a 2,400 pound Shorelandr.

Everything is fine when I pull the boat during the day, but once the automatic lights in the truck turn on, I lose my cruise control and the left turn signal won't flash.

I have tried different plug adapters and different vehicles, but the problem persists.

Where should I start and what should I do?

Thanks.

If your handy at all, make up 4 short jumpers, with male bullet connectors at one end, females at the other. Hook your 4-pin connector to the tow vehicle, with the jumpers in between. leave the ground jumper connected, but 1 by 1 remove a jumper (left turn, right turn, running lights). When the problem goes away, you know which circuit to look at. My guess is that you'll find the problem in the left turn signal circuit, since the cruise thinks the brakes are on (and won't activate) and your left light won't flash. Honestly, sometimes it's easier to run a whole new harness than it is to find the frayed spot on the wire.
HRG

by any chance are the vehicles you tried towing with fords? your cruise has nothing to do with the trailer lights. that part of the BCM (body control module) i believe. you might find it's between your VEC ( vehicle control module) and your BCM. a simple fix. most any dealer should know exactly where to look.

I pull the trailer with Chevys...

I dont think its a module issue if it happens with more than one vehicle.

And the cruise may have to do with the trailer light circuit indirectly.

You may have a problem with a brake light bulb or circuit. The cruise shuts off when you apply the brakes, the cruise may get the signal to shut off from the brake light circuit.

that curcuit/switch is on the brake pedal brkt. it's shut off buy that switch independant of the lights ( safety item). and would have to back feed, which anything is possible but not very likely. since it's the left side showing the problem, i'd start right there on the trailer. simple stuff first. bulb/receptical, ground. if you know how to use an ohm meter or ( tester light), check for a ground on each wire where there shouldn't be one.
since you say it happens the same way using other vehicles then you eliminated the vehicle being a problem. ( except there were some fords that had a real goofy wiring problem back a few years ago). if a wire is grounding out look for insulation being worn away possibly where the wires are run thru places on the trailer as it runs down each side. you might have some corrosion to were only one or two strands of wire are trying to carry the load and that doesn't work.
if your trailer is older, myself, i'd save the time and just run a new harness with new plug. protect the wires where they go thru holders etc. install the new LED lights. seal all connections. the light kits range from $40 up and every style available.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=95974
i've had problems with every trailer i've owned and found it better to just get fix it myself one last time and not have to be out there at 4 am trying to solve a light problem. and with the LED's they are much brighter than regular bulbs. folks behind you can actually see when your braking/turning.

I'm not saying this is your problem, but it sorta matches the symptoms you describe.

I once had a problem with my trailer wiring. The short story is mice had moved into the trailer frame and chewed most of the insulation off the wiring. The lights usually worked in dry weather, but if I was driving in rain at night the tailight fuse would blow. There were some other odd behaviors, too, with the wires shorting to each other.

The problem was hard to trouble-shoot when everything was dry, but once I ran some water through the frame with a hose and jiggled the wires, I could measure a short from the light hot wires to the frame.

Where should I start and what should I do?

Thanks.

I know what I'd do...go buy new wiring. You can spend hours trying to track down the culprit...and may not even find it! You can buy the entire kit for $40 or buy just the wire and connectors for about $15.

Rewiring the trailer takes about an hour with the kit. Wiring gremlins and trying to find them can have you pulling your hair out...make it easy on yourself and buy new wiring.

BIRDDOG

This is common a Shorland'r trailer, had the same thing happen. The trailer wires rub on the tube frame of the trailer and wears a bare spot on one of the wires. Sometimes its ok and then it happens, a blown fuse. On my Ford if it happened the turn signals wouldn't work. Then you knew something was wrong! After repairing the wire twice I plulled them all out and taped flat electric light cord to the outside of the trailer frame, no more trouble.....

Where is a good place to buy a wiring harness and LED lights on-line?

Where is a good place to buy a wiring harness and LED lights on-line?
Isn't there a Fleet Farm store near you?
HRG

Where is a good place to buy a wiring harness and LED lights on-line?

Northern tool, Fleet, tractor supply...etc.

As far as preventing this from happening again, if infact this make trailer has issues with chaffing wires. Run some conduit the length of the trailer. Fish tape it through. I ran coduit on a few of the trailers I rewired, makes for a nice clean install.

BIRDDOG

that curcuit/switch is on the brake pedal brkt. it's shut off buy that switch independant of the lights ( safety item). and would have to back feed, which anything is possible but not very likely. since it's the left side showing the problem, i'd start right there on the trailer. simple stuff first. bulb/receptical, ground. if you know how to use an ohm meter or ( tester light), check for a ground on each wire where there shouldn't be one.
since you say it happens the same way using other vehicles then you eliminated the vehicle being a problem. ( except there were some fords that had a real goofy wiring problem back a few years ago). if a wire is grounding out look for insulation being worn away possibly where the wires are run thru places on the trailer as it runs down each side. you might have some corrosion to were only one or two strands of wire are trying to carry the load and that doesn't work.
if your trailer is older, myself, i'd save the time and just run a new harness with new plug. protect the wires where they go thru holders etc. install the new LED lights. seal all connections. the light kits range from $40 up and every style available.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=95974
i've had problems with every trailer i've owned and found it better to just get fix it myself one last time and not have to be out there at 4 am trying to solve a light problem. and with the LED's they are much brighter than regular bulbs. folks behind you can actually see when your braking/turning.

On my Ford F250, the brake lights and the cruise control are on the same fuse.

thats why I think its all related to the brake lights on the trailer.

As far as a good place to buy led lights, I got mine from ebay, there is a truck-trailer parts store there that had name brand lights for 1/2 of what you can get in stores, I bought from him and they are great. $40 for the pair and they are $79 everyplace else. This was about a year ago. I can dig up the guy (he has an ebay store) if you like.

Perchjerker
Go right to your vehicle dealer... I had trouble with my snow plow lights, everytime I would unhook the plow with lights the module would send and recieve false signals. In other words the plow company and the truck company weren't in-sinc or updated in their electronics.
Example: I believe newer truck modules are designed to respond to LED trailer lights. So, if you hook up an old trailer and one of the lights is out it will send a signal to the brain and after so many signals it tells itself to shut off...
I may be wrong but that's where I would start.
With my truck it was a matter of a simple download update from Dodge..........Paul

my lights work fine....

but thanks for the info

"On my Ford F250, the brake lights and the cruise control are on the same fuse"
they could be on the same fuse ( to get power but! the cruise is it's own curcuit thru the (BCM) as far as turning/shutting off due to legal safey issues... has nothing to do with the break lights. that's why there are 2 switches controlled by your pedal.

"On my Ford F250, the brake lights and the cruise control are on the same fuse"
they could be on the same fuse ( to get power but! the cruise is it's own curcuit thru the (BCM) as far as turning/shutting off due to legal safey issues... has nothing to do with the break lights. that's why there are 2 switches controlled by your pedal.

yes I understand that Tom....

but if the trailer brake lights cause the fuse to blow that also powers the crusie control...it wont work either...thats my point....

I had the same problem on my Shorelander trailer. It was so frustrating not to be able to pinpoint the short. Finally got wise and took off the tail lights and pulled out the wiring. I had a 20' piece of garage door cable and ran it in the frame, back to the grommets just behind the wye in the frame. I then tied the new wiring to the door cable and as I pulled the new wire through the hole I wrapped it with spiral wrap. I think it came from Home Depot. Have not had a problems since. I just wonder if you continue to back the trailer in the water at launch, what is the possibility of rusty flakes with sharp edges developing inside the tubular frame?

Redpete,
Pull out the old wiring and pull in new wiring.
If possible, (depending on your trailer construction), pull in a piece of pvc tubing inside the trailer frame. Then, run the wiring inside the smooth sides of the pvc tubing.
Extend the pvc tubing out of the trailer frame, so that there are no sharp edges to cut the wiring during use.

Put new led lights on the wires, and a new connector on the end and you will be good to go for as long as you own the trailer.

p.s.
I also run a section of rubber hose over the end of the wire as it comes from the trailer to protect the pigtail as it goes to the vehicle.

Take care
REW

I had a similar problem with a swing tongue trailer I used to own. I had pinched the wire harness when I swung out the tongue and locked it . The wires were not broken but the insulation was crushed enough to cause a low level short.

Check your connectors that plug into the back of your lights. My Shorlelander kept blowing fuses in my Dodge truck this past year. Turned out that one of the connectors going into one of the running lights came loose and when the connector hit/rubbed the inside of the trailer, it would short out. I squeezed the female end tighter with a pliers so the connector had a tighter fit. Problem solved for zero cost. Only 15 minutes of my time.