i am no wiring genuis at all, done the search and nothing. would anybody know why the back up light fuse blow only when i plug in a trailer. i have two diffrent trailers and they both do it. i cant seen to find a short any where.i think it is only happing when i put the truck and trailer in reverse. thank you for your responce

 

Maybe there is something wrong with the female plug on the truck or a short in the wiring.

 

i will have to check the truck side.i thought truck would have been fine because it only does it wiht a trailer. thanks for the reply back to the drawing board.

 

Which type plug are you using? Are you using a factory 7 or 4 pin receptacle with the harness that plugs into the existing wiring?

EDIT: Which fuse are you talking about exactly? Do you have the under-hood fuse box that comes with the towing package? If so, is it fuse #4 that is blowing? The attached chart shows a towing backup lamp fuse (#4) and a relay (#38).

 

it is the under the dash fuse. it is a 15 amp fuse #28. i have used both 7 pin and the 4 pin one for each of the trailers that i have, an 8 ft and a 20 ft. thanks for the reply

 

Hmm, interesting. My truck is a 99.5 so it might be different from your 2001 model . I'll give my thoughts assuming they are the same unless you verify otherwise.

Fuse #28 under the dash operates several different items. (see attached pdf). The back up lamp is one of these items. However, I assume this fuse does not blow while driving around without a trailer, correct? Just to rule out the obvious, I would check the wires going to your brake pedal switch and the bundle of wires on the bottom of your steering column (right behind the access panel that is removed to get to the fuse panel). Look for any bare or damaged wires or anything abnormal.

Assuming you have the under hood fuse box as well, look in there and make sure there isn't anything weird. Check the underside of the plastic lid for any burn marks. Then pull fuse #4. This should be for the Trailer Backup Lamp Relay and the trailer running light relay. I don't know where the actual relay is (perhaps just to the side of the fuse box) but pulling the fuse should disable said relay. Then hook up your trailer and put it in reverse and see if your under dash fuse blows. If it doesn't blow, then you know your under dash wiring is good and the problem is post relay or possibly the relay itself.

If your fuse box is different than mine, then I am out of suggestions. Do you have the under hood fuse box for the trailer tow package?

 

as sugested i have no issues driving around town. and yes # 28 fuse under dash does control a # of things such as speed control module , back up lamps,trailer tow backup lamp relay coil,electronic shift on fly hub lock,vacume pump motor. i did not notice any of those things not working before the next morning, when i backed out of the garage and no back up lights. the # 28 has poped in the past and i thought nothing of it but a bad wire on the trailer. so tonight when i get home i will check the under hood box for anything weard, and check the # 4 20 a fuse maby the # 4 20a fuse blew some time ago and the undre the dash is taking the blunt of the reverse amprage
thanks again for the reply

 

Sure thing. I'll pm you with my cell number in case you want to call with any questions when you are checking out stuff.

We both will probably learn something from this because I am curious how you can blow the #28 fuse under the dash without blowing #4 under the hood as well. In addition, it's weird that you are blowing the fuse while using the 4 pin flat plug because that one doesn't even carry the back up light current anyway. I am not too sure how everything is wired up myself but I suspect the #28 fuse under the dash operates a circuit that provides power to the under hood relay when the gear selector is in reverse. That relay may then be what operates circuit #4 under the hood that actually sends power to the 7 pin trailer plug. If this is the way it works, then my money is on a bad relay. If you had faulty trailer wiring, then you wouldn't blow the #28 under the dash when using the 4 pin flat plug (at least I don't think so...)

Also, #28 under the dash should be a 10 amp fuse, not a 15 amp like you mentioned on your original post. This might be a clue that a previous owner my have had problems with the reverse light relay and installed a larger fuse to solve the problem. Are you the original owner?

 

Just throwing this out.... Either trailer have surge brakes?

 

first off thanks for the help My BAD i failed to mention that the two times that the fuse poped i had my cab over on the truck. so now i need to fugure where it is wired wrong. i only have three wires comming from the cab over, hot comming from the truck batt witch has a switch to the 12 volt batt in the cabover,one for running lights and a ground. i will have to check under the truck wire loom in witch the cabover is wired to. i might have wired somthing wrong i will have to get a wiring diagram any ideas.

 

Sure, here is a wiring diagram for the 7 pin plug. Because you have a house battery, you should be using the 7 pin plug at the back of your truck, correct? If so, check the trailer side of your plug and make sure the ground is wired to the White terminal as per the attached picture. The battery charge wire connects to the black labeled terminal and the running lights connect to the terminal labeled Green.

Don't get hung up on the actual color of the wires for right now, just look at the attached photo and check your camper wiring. If it is wired correctly, then we need to check the plug on your truck side. That gets a bit more confusing because the Ford wiring harness changed the colors and they don't match up to what is shown here. I will attach a photo of the harness and the label on the harness in case we need it later.

Based on your recent post, I suspect that you will find that your ground is wired to the center terminal by accident. Let's hope the fix is a simple wiring issue and you are good to go.

 

thanks for the photos they will help. now i have something to do this weekend, wiring is not my favorite thing to do. i think that i have more of an issue with my cabover wiring to the plug in the bed of the truck.now that you hooked me up with the photos, i will check the connect from the plug to the loom using the ford factory harness photo.

 

here is a photo of the truck and cabover

 

I know it’s an old postings but my truck also blows the fuse under the dash for the Reverse lights when I have a trailer plugged into the 4 pin. Has anyone found the cause of this? I haven’t checked the fuse under the hood but I will guess it didn’t blow as I have lights after changing the under dash fuse. I haven’t tried the 7 pin yet but both times I pulled with the 4 Pin I had to change the fuse. I’m still looking through all of the post that came up on the search result so I may find my answer but wanted to post here just in case.

 

If the fuse only blows when a trailer or slide-in is hooked up, it is unlikely the problem with both the trailer and the slide-in and since it only blows when hooked up, there is an error in the wiring at the plug.

Steve