Would anyone be able to tell me where I can find my trailer tow battery relay in my 1999 f-450? It has the plug for the brake controller and has all the wiring to the rear but I believe the relay was never put in from factory since it never came with a hitch.

 

Sorry I don't have my manual in front of me, but the fuse you're looking for is under the hood, driver's side up on the firewall. It's a maxi-fuse and your owner's manual should tell you which one and the size (amps) required. Often even though the wiring is there, the fuse wasn't installed.

 

Have you checked to see if the battery wire is hot on the plug?

Otherwise if the owners manual doesn't give the information, a camper place can probably tell you.

 

The maxi-fuse is there, the mini is there, the wire at the plug is not hot. In the manual it says a relay should be located near master cyl. I have found a relay box behind glove box with 2 relays in it, one big one small. Spoke to r.v. installer and 2 ford shop formans, they all think it should be near master cyl. as-well but it's just not there!

 

Are you checking the wire with the key on or off? The battery wire in the 7-way plug will only be hot with the key in Run.

 

I have been checking in run position. Well I think it time i just find the wire in the harness , splice it and run a new one to the power box. Thanks for the tips.

 

Looking at my manual which should also cover yours, there is a fuse and a relay under the hood:
16, Trailer Tow Battery Charge, 30 AMP (located in the pwr distro box)
39, Trailer Tow Battery Charge Relay (located in one of two small black boxes between the PD box and the brake master cylinder.)