Tow Package Trailer Wiring Fuse and Relay Locations for a 2008 Ford F-350 Diesel

Updated 06/11/2024 | Published 02/07/2016

Question:

I have no power to the 12 volt post of my trailer plug. I have checked the fuse in the truck cab and the fuse in the main box . Is there a relay ? I just purchased the pickup and this is the first time I tried the plug. Everything else works. I cleaned all the terminals on the plug they look good.

asked by: Doug S

Expert Reply:

There is a relay for the 12 volt circuit on the 7-Way in your 2008 Ford F-350. There are 2 fuses and 1 relay related to this circuit. The relay is in location 56 in the power distribution box under the hood. As you said there is one fuse in the cab in location 33 and one in the power distribution box in location 44.

The following are the other relay/fuse locations for the tow packaging wiring on your truck:

Under the hood
Location 5 - fuse for brake controller
Locations 20 and 21 - relays for trailer turn signals and brake lights
Location 34 - fuse for trailer turn signals and brake lights
Location 42 - fuse for trailer park lamps
Location 55 - park lamp relay
Location 63 - fuse for trailer backup lamps

In addition to cleaning the pins on the 7-Way I also recommend cleaning the connections in the back of the connector where the wires attach.

expert reply by: Michael H

Boyd

9/4/2020

I add another plug in the bed of my pickup. It is a 2008 f350 and since then I have been getting trailer disconnect messages with an alarm. I was told it changed the resistance in a tester and I could get a plug to put in the connector I was not using. If so what is the name of the plug?

Jon G.

9/4/2020

Do you mean an adapter like the Tow Ready # 20142? This adds a load on your 7-Way and is typically used when a trailer has LED lights and the vehicle has trouble sensing that it's connected.