So I’m always disappointed when I come across this, but I bought a 95 f250 psd and wanted to add a trailer harness. Unfortunately the truck didn’t come factory with a tow package. TBC is plugged into the factory plug under the dash. Unfortunately the firewall harness plug does not have the wires, but all of the trailer fuses and relays are there. Does anyone have under hood and trailer wiring harness diagrams ? I have a firewall plug from another truck I can add the wires in for a factory-like installation. TIA

 

Here is the wiring:
Attachment 277956

Attachment 277828

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if you have the two plugs with 7 wires under your rear of truck, ccut them off and wire all the wires to adapter, you just wont have charge and reverse and brake function till you address those later

 

Thank you very much for the diagram, I will update with pictures

 

My truck had trailer package, and was missing the DB wire, from C205 to C424.
I had to tap into C205, and add that wire.
TBC then worked.

 

thats strange :O
Wonder if maybe the wrong "harness" for the truck was put on? Or possibly just an oopsie? even my truck has a blue brake wire running to the back in the 2 oem plugs, although I did not have a trailer package or a trailer controller.

Well, someone put a trailer controller, but they ran their blue wire for trailer brakes inside an outdoor extension cord ..im just grateful they only added and made work harder for themselves but left factory plugs and wires alone. Only nonsense they did was the wire taps under the dash for the brake circuit which I got that out of there and sealed the incisions

 

Subford, do you have a diagram of the under hood PDC? C149 is not on this harness, so I need to see where the relay outputs go to tap in.

 

The two connectors for the relay box (C105 & C149) should be there with dummy caps on them if you did not have the trailer tow package.

Attachment 277926

My wiring diagram to convert my 1995 F150 from non factory trailer wiring package to wiring for the trailer relay box 17 years ago.


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Im assuming you just cut the Connector bodies on the end of the truck since you cant buy that mating half anymore and the factory plug in things are old or expensive and often have a round 7 way not the blade.
I just got a universal 4 flat / 7 way and stole my functions from the 2 plugs and then I will get the relay box at some point and then I will have 2 additional wired pins on the plug.

 

So I only have c105, which I realize now is the feeder for the 2 trailer relays, which in turn has c149 as the output to the trailer harness. I will find said relay kit and install, then update with all the pictures etc

 

you dont have 2 connectors or are you saying you have an original harness already and its hooked to that one?

 

I only have the one black connector because I don't have the two additional relays which would give you the second connector, which means I'll have to add wire #8(trailer charge signal) to the firewall plug and maybe tie one more for the trailer backup lamps.

 

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Resurrecting this thread because I am having a similar issue to the last couple of posts and all of the right diagrams are on here.

94 f150 with no factory tow package installed. I only have plug c105 under the hood and no c149.

picked up the trailer relay box and plugs from my local wrecker and I am just going to run the battery, backup light and brake controller wire to the back of the truck separately.

I just need to figure out where the best place to tap into the relay signal wires would be for c149?

It looks like the backup light is circuit 140 Bk/pk and I should be able to tap into pin 24 of c205.

battery power signal comes from circuit 298 P/O and it looks like I can find it in pin 8 of c205 or on c202 pin 32 (looks like it goes to circuit 886 O/BK on the male side of the plug c202? According to diagrams)

First time posting on any forum for a long time. It looks like @subford has this pretty much figured out and has posted on it every couple of years for the past 10-15 years.

It’s appreciated to have access to that kind of knowledge and I wouldnt have gotten this far without it.

Thanks!