Still working on getting my 7 round trailer plug working on my truck. Bought the plug in for it because the truck has the trailer tow package. The previous owner had hacked the crap out of the plug in on the truck side, so I ended up cutting off the ends and just hard wiring it. Everything works perfectly except for the hot wire. I have no power going to the plug. The fuse is good. The only thing I'm not sure of is the relay. The manual has it listed as relay #38 but I can't locate it anywhere and it doesn't show it on the schematic in the manual. The hot wire should be the orange one, correct? I'm getting no power from in front of where the hack job was (where it is still factory wiring) so I know that isn't the problem. I'm thinking at this point I'll just hot wire in a wire from the battery. I know I'll have to fuse it, but what size in line fuse should I use? Also, what color wire is it that I should be tapping into?

 

You know the wire is hot only with ignition on?
The circuit should be 30 amp rated with #10 wire, although some trucks have #12.

 

Yes, I checked it with both the ignition on and then with the truck on.

 

there was a pic posted of the relays the last time we had this conversation..

right next to the master cylinder.

Sam

 

Yup, I looked and I do not have that relay box, just have the power distribution box.

 

I have never seen a stock truck come with a hot wire, maybe the newer ones do. All my own vehicles had to have a hot wire run. On mine, it is always hot, direct power off the battery. It is fused of course. I'll bet your setup has no hot wire and thats why it doesn't work.

 

All stock Fords for a very long time (at least '96), came with factory fuses, relays, wiring and at least a connector for a 7-pin wiring harness under the bed.

The question is where is the relay. It depends entirely on the model year. Mine is in the Central Junction Box under the dash. Some are in the Power Distribution Box. Some are apparently in a relay box next to the PDB.

To the OP. You might try ALLDATAdiy.com :: Leading Source of Diagnostic and Repair Information. It will cost you about $25 for the first year subscription. But it will have all of the MY specific wiring diagrams and locations and stuff that you need.

 

I thought that relay box was located under the hood.

 

but you DO have a wire at the rear connector for power?

sam

 

The attached diagram is from the service manual for a 2004. I believe 2002-2004 will be similar. This diagram doesn't apply to the OP in any way BECAUSE IT DEPENDS ON THE MODEL YEAR!!!

 

but I think he is working on a 99..based on his sig

Sam

 

After digging further into this today I found that there is a bracket attached to the PDB where the relays should be, but there is nothing there. Someone had hacked it off at one point, probably to install the AFE intake it has from the previous owner. There were not wires in sight for it. So, I just wired a fused hot wire from the battery to the wire on the back of the trailer plug. It works great, but of course it always hot, so I'll have to remember to unplug the trailer when turn the truck off, right? My truck has dual batteries, but I just don't want to drain it.

Also, my pin for the back up lights on a trailer does not work either (probably again from the missing relays). Is this an easy wire in job or more complicated? I really don't need them as I don't have any trailers yet that have back up lights. Thanks again for all the help guys.

 

if there is no load at the trailer, then there would be no load on the battery.. (ie don't leave the inside light on, or charge a separate battery)..

or, install a relay there and find a switched lead to control the relay

hot power in on 87, out to trailer wire on 30
ground on 85, switched power on 86.
when 86 powers, it closes the circuit with 85, an triggers the relay to close the link between 87 & 30..

relays are like $5 at autozone, or wherever..

roughly the same.. drag a new wire back there, connect it to the backup light wire in the cab (currently black with pink stripe, don't know for 99)
or again, use a relay, and have the current wire on 86 trigger the relay to send power from pin 87 to pin 30(to the new wire)

Sam

 

It takes a lot to discharge the dual batteries we have. I can use liftgate for loading like 20 times or my 8000 lb winch for pulling vehicles 100 feet from the corner and never had to worry about draining the batteries to the point they would not start the engine.
The only trailers I heard have back up lights are luxury horse trailers and they usually use powerful halogens that require separate power source to run.

 

my enclosed car hauler has backup lights..

sam