One thing you can try is by-passing the factory harness. CUT the wire about 4-5 inches downstream from the fuse and 4-5 inches upstream from the trailer plug. Then run a 10 or 8 gauge wire and heat-shrink-buttsplice it between the two points. If that works, you know there is a corner SOMEWHERE that is going direct to ground.

IF it still blows after that, you know it is either inside the plug where the wires connect at the trailer connector OR it is inside the fuse block itself.

 

Is it always the same trailer when it blows or is that random?

 

I am ASSUMING it is popping the fuse WITHOUT a trailer. If it happens immediately when it's connected, it would obviously be the trailer.

 

Thread moved to electrical forum.

 

If you are connecting the trailer with VERY low batteries it will blow the fuse. Not sure what your trailer is or how the wire is used on that end but it is one possibility.

 

The bypass suggestion is good.
Have you checked the wires inside the loom front to back? Also check the blunt cut wires under the cab rear/box front in the frame, or in the box trailer plug if you have that. I had a sloppy box trailer plug give me cross feed and problems popping fuses.
Do you have more than one battery in the trailer? May draw to many amps is the batteries are discharge.
And does the accessory wire in the trailer light cord go directly to the trailer battery? or is it dead ended against the frame someplace. Look in the junction box on the trailer where the light cord should tie into the trailer wiring. Check continuity/shorts in that junction box both forward and into the trailer.

 

We still need to know if this fuse is blowing just driving around WITHOUT a trailer? Or WITH a trailer?

 

ok guys, thanks for the feedback, here goes additional info....

Not sure if it is blowing before I hook up to the trailer(s) but I find it immediately afterwards.

Trailers in question are a homemade dumpbox trailer I use to haul crap to the dump, the lift is an electric winch and pulleys over a Sampson post. If the winch don't turn the fuse is popped. (no brakes on this trailer)

2nd trailer is the TrailsWest Horse trailer with living quarters, If the LED on the brake controller isn't lit, the fuse is popped.

3rd trailer is a 2012 28' Prowler, same as the horse trailer.

4th trailer is a 1959 Ajo 16' camp trailer, same as the horse trailer and the Prowler.

I don't remember checking the fuse prior to hooking up to any of these, only after. So I can't tell you if it is immediately during the plugging in action or before. And it happens very randomly. Like I said, it may go a year before it happens or it might happen 3 times in row (with a few weeks between connecting to a trailer). Once the fuse is replaced all is good during the tow.....

My thoughts are the same as pa32rt, but because I found this on a different 2002 Dmax, I was wondering if the issue is chronic and the location of the short is identifiable.

Anymore questions or ideas?

 

Nevermind the bypass. You need to BE SURE that it is either popping WITH or WITHOUT a trailer. Diagnosing TWO units is twice as hard.

STEP ONE:

Replace fuse. Drive for a week and use a light tester to check for power at the back end OR just check the fuse.

IF it's fine after a week WITHOUT a trailer, hook up trailer. IMMEDIATELY check the fuse. If blown, you know it's a dead-short in the power supply to the trailer.

Let's just go from there.

 

pa32rt - been there done that on numerous occasions. I cannot duplicate the issue. It happens at random. Like on Friday.... Last week I used the truck/junk trailer with no issues. Fuse good before and after use. Friday I connect to the new trailer - fuse blown. Removed connection to the trailer, replaced fuse, reconnected and used the trailer for days during the Memorial Day weekend. Parked trailer at home, fuse good. Reconnected trailer to go to town and dump the black water tank, fuse is good yesterday and again this morning still good.

Does not matter what trailer which I connect to. I BELIEVE, but can't prove, that the fuse is popped before trailers are plugged in not because of the trailers. Unless I use the examples that the fuse is good after I disconnect the trailers. (I have 5 trailers - 5 with brakes/running lights, 2 of those with batteries - that the accessory line charges those batteries, 1 with only tail lights and brake lights.)

 

About the only thing I can add is - disconnect the battery charge lines from the two with lifts/batteries, whatever they have. Use trailers that ONLY have lights and brakes. No accessory power(s). Keep hooking them up, drive around the block, and check the fuse.

What I am getting at is - seeing if the charge lines for those specific trailers are the culprit.

If it were my setup, I would be checking the trailers I tow and make sure all of the plugs are wired the same. Charge line in the same position and such. I plugged in a trailer the other day to the pu, and the lights were all funny. Ends up, someone had re-wired the trailer to big-rig specs. Wired it back to normal and everything is fine.

 

Just as a followup. I have not found the source for the 40 amp fuse blowing, I ran the entire wire from the fuse box to the trailer socket....nothing. So I ran a lead from the hot side of the same fuse to a auto reset 40 amp breaker to the trailer socket at the bumper.....no more problems!

Not my first plan but it works and that is the main idea!!!

 

FINAL!! FOUND THE ISSUE

It appears that there have been lots of viewers and few comments.... ok fer me cuz my comments were mostly cuss words!

I think I finally found the issue, though I over came the problem of the blown fuses by running a new hot lead to the rear bumper/trailer connection, when I decided to 'electric-fy" my hoist.

The inter-connect to the outlaying female plug was not making a good contact. There was about <1/8" gap with the slot connection and therefore an "intermittent" connection. Rapid intermittent contacts causes undue stresses on fuses thus the constant failures I was encountering. (I think!)

I replace the wiring and directed contact to the battery and added a self rest 40 amp fuse, and it 'fixed' my issue(??) until I used the connection to power a winch on my lift. No Power - - - ????

When I remove the receptacle from the socket, I discovered that the 'hot' lead was gaped open < 1/8" but not making a constant contact.....fixed and it 'seems' fixed.

Fingers Crossed.....

BTW the 'lectric winch on the hoist is a rear weiner!!!! :thumb: