Ford E-350 Ambulance trailer wiring help needed.

[Ambolorian]

Greetings!
I'm new here and could use a little help with a wiring question.




Backstory is that we recently picked up this 2002 Ford E-350 Powerstroke 7.3 from the hospital where my fiance and I work.
I've since removed the light bar, decals and the mustache (I miss the mustache.)
I installed a Curt hitch and I'm trying to run a new harness but am having some issues with finding the correct wires.
I believe this is considered a "Stripped Chassis" and as such there are no trailer wires that you would typically find tucked up behind the rear bumper or along the driver's side rail. I did verify that I have the towing relays and all fuses accounted for in the under hood fuse box.
After purchasing a Ford Wiring Diagram book for the E-Series I was able to locate the brown plug under the driver's side dash for the Brake Controller (C248). Above "Trailer Electronic Brake Control Connector" on the right.





I also located a Gray plug under the dash (C238): Look under Modified Vehicle on the right.


The schematic shows where its going but not where the wires originated.

The plug holds six wires and after some extensive testing with a volt meter I found the following:
Light Green/White Stripe- L turn signal
White/Light Blue- R turn signal
Dark Blue- Trailer Brakes?
Gray/Red- ?
Yellow- Power
Orange- Trailer Battery Charger?


These wire colors don't match anyone else's color codes and I think I'm missing Running lights, Ground and Reverse so I'm just trying to verify what I'm looking at before I try to reinvent the wheel.

Does anyone have any experience with these rigs that can chime in?

Thanks!

 

[motovan_mn]

No specific experience with this rig, but are you just trying to wire up the lights on your trailer? If so, couldn't you tap into the brake/reverse light wiring at the back of the van? Or are you trying to avoid this for some reason?

 

[Ambolorian]

Thanks for the reply motovan_mn. I wish it was that simple.
I have an Airstream I'll be towing with a 7 wire plug that I need to supply with power.
In addition to the lights I need the 12 volt charge for the battery as well as the feed from the Brake Controller. I'd like to use the van's tow package relays so I don't over tax the system but I'm struggling with reading Ford's schematics. Not my forte.
Thanks for the reply.

 

[Bikersmurf]

For power and charging I connected to the ambulance circuits and “house” batteries. There’s more power available there than the OEM trailer relays would ever provide.

If you’re still running a diode isolator I’d highly recommend switching to a Blue Sea ACR (or equivalent). Deep cycle batteries are always better than starting or “marine” batteries for a sustained load over time.

So far I’ve not connected the brake controller… only a powered brake controller which only uses the stock wiring for a signal.

 

[nated]

@Ambolorian , did you make any headway on this? I am currently with the same era (2001) vanbulance wanting to add a brake controller and 7 pin harness. I've got a pretty good parts dept. at my local dealership, going to try there to see if they can shine some light. The grey plug would be for a brake controller, I don't have anything run under the van as far as 4 pin or 7 pin. The CURT Manufacturing 56020 looks like it will tie into the brake lights for 4 pin, and then it's just a matter of running cable from the fusebox for trailer brakes and 12V.