Bishophiker

I have a 2016 f150 xlt. When connected to my travel trailer, the fuse (#34) for the "Trailer tow park lamps" (running lights) blows although not immediately. The service folks at the trailer dealer checked the trailer and say that it is not the problem. Any suggestions in resolving this would be appreciated.

ifallsron

I'd start with an inspection your 7/4 outlet. Look for discoloration and funk on the tabs. Then follow the wires upstream.

The 34 can be responsible for other high energy surges like fuel and AC pumps. Your trailer could provide the weak link.

Bishophiker

Thanks! I will see what I can find tomorrow.

PerryB

Please elaborate

PerryB

If it doesn't blow when not connected to the trailer, it's NOT the truck. If the problem was a short in the truck's wiring or bridged terminals in the plug, then it's possible to blow that fuse even when not connected to a trailer. If it only happens when connected, the problem has to be with the trailer. Of course the dealer says it's not the trailer, they don't want to have to fix it. Most likely you have a pinched wire in the trailer body that shorts to ground when you hit a bump. Make the service man get in with you and go for a ride with the parking lights on, it'll be easy to tell when the fuse blows. Sitting in the parking lot, it may never pop the fuse.

Steve83

Find the specification for the current needed by the trailer marker lamps circuit. Install an inline fuse (or several in parallel) in the trailer wiring as close to the truck connector as possible. If the spec is 11 Amps, use a 10A fuse (which is designed to carry 11 Amps for 1,000 hours without blowing, but should blow at 13A in less than 1 second). If the spec is 9A, install 2 fuse holders in parallel with a 7.5A fuse in one, and a 1A fuse in the other (or some other combination approximating 9A capacity). The trailer fuse capacity MUST be lower than the truck's fuse rating. Click this & read the caption for more information.


(phone app link)

If the truck fuse blows and the temporary trailer fuse(s) doesn't, the fault is likely in the truck. If the trailer fuse(s) blows before the truck fuse, the fault is absolutely in the trailer.

PerryB

If the fault is in the truck, it's going to blow #34 whether there's a trailer connected or not. It's a stand alone circuit, not tied to the truck's parking/running lights.

Steve83

If the fault in the truck only draws the fuse's rating or slightly less, then the fuse won't blow until a trailer is connected. Even a trailer w/o faults.

kbroderick

Can you wire up a dummy load equal to the trailer lights' expected draw and hook it to the truck, or even test with another trailer? If it's not the trailer, you should still blow the fuse. If it is the trailer, you won't.

Flamingtaco

Yes. There CAN be an issue in the truck, and the circuit is flowing more current than it should, with the trailer pushing it over the edge. I'd do a current check on the fuse without the trailer connected to see what is flowing through it nominally.

At the same time, trailer wiring is an afterthought with most mfg's and due to this, often a source of problems. I pull a 16ft Haulmark that has braced holes in the cross members so that wiring could have a protective casing. Casing? Hell no! They didn't even wrap the wires, just installed them bare! The number of small dump and boat trailers where the wiring could be run through the tongue bar, but isn't, is plain infuriating. Lazy bastards, the lot of them.