99 F-250, 7.3

Trying to install a trailer brake controller in my new to me pickup. Picked up a fancy Tekonsha P3 controller(P/N 90195) off Amazon with the plug adapter(P/N 3035-P) for my year of pickup. Plugged it in and nothing, got out my test light and checked, no power at plug to the back of controller. Checked fuses under the hood and they are good. Plugged in a trailer to make sure that it didn't need something plugged in to power up and still nothing on the controller, trailer lights worked though.

Am I plugged into the right plug under the dash? The connector went in just fine. Should I wire the pigtail in to the loose wires instead? Almost looks like the previous owner had something there, since they are snipped clean with no covering over the end.




Red arrow point at plug for trailer brake, holding other loose wires

 

Just went thru a similar exercise, bought the basic Tekonsha controller and the #3035-P cable. Said a prayer, plugged it into my rigged-to-hell F-250 (same socket as you) and my trailer brake controller worked first rattle out of the box.
The bad news: I just went thru the Ford Factory wiring manual and could not find the the truck socket which the #3035-P cable is plugged into. It must be in the manual, but I could not find it. Extra points to the tech who does find it! The only information I found is that a conductor #43, which is Dark Blue, goes to the Trailer Plug at the rear bumper.
The good news: I have wired a lot of these controllers in the past into old-fashioned trucks, there are only four (4) conductors needed: 1) Chassis ground, 2) 12 VDC power for brakes, 3) switched 12V when brake pedal is mashed and 4) said #43 Dark Blue conductor going to trailer brakes.
You may have to bite the dust and probe around to find the appropriate wires then either butt splice em or butt splice them back to the socket which accepts the #3035-P cable. Not pretty, but suspect one of the previous owners installed a brake controller and did not have the #3035-P adapter cable..
I will make a wild guess that the Black (or maybe White) wire shown in your photo is chassis ground. Leaving two unknown wires, one of which will be full time 12 VDC and the other "switched on" 12 VDC when the brake pedal is mashed.

 

Maxi fuse #28 under the hood provides power to the trailer brake controller.
There are several fuses and relays in that under hood box that are used by the trailer wiring.
Look in the owner manual page 150 for the diagram for this box.
If you don't have an owner manual download it here:
http://www.fordservicecontent.com/Fo.../99f23og4e.pdf

Make sure you are testing the correct wire color on the trailer brake controller connector: The colors for Tekonsha are:
Black - Battery Power
Red - Stoplight Signal
White - Ground
Blue - Output to trailer

It is possible the TBC is faulty right out of the box. Not likely, but possible. It is more likely that the wiring has been munched over the last 18 years.

The wires in your hand in the pic are for the customer access pass through wires, or upfitter switches. That is how Ford left them, blunt cut & dangling. The don't connect to anything, they are there to make it easier to hook stuff up by already having a wire run through the firewall. The other end of those wires is next to the master cylinder. The trailer brake controller appears to be plugged into the correct socket, that's where mine is on my '99 SD.

You will want to check to be sure you have all the correct relay slots populated. The underside of the lid on my 99 that shows the slot #s is not numbered the same as the diagram in the owners manual pdf. Mine is an early 99. The lid shows the relays are numbered 1-6 and the pdf says 30-35 with the diode as 37. Mine also has 2 relays in a separate box hanging off the side right next to the master cylinder, guessing that is 38 & 39 on the pdf. There is a different bracket to the front of that that is empty, my guess is that would be for the ESOF relays but mine is 2WD.

 

I know on some trucks there are 2 different master cylinders that could be installed depending upon if the truck came from the factory equipped with trailer braking option. The one for trailer braking has electrics to connect to the controller. Also, just because it has a trailer braking master cylinder doesn't mean it also came with the factory controller inside. You need to check to see if your truck has the proper mc...if it applies to your truck.

 

I would be surprised to see a 7.3 that was not originally equipped with the tow package.

 

That fuse and all the trailer fuses are good and getting power


Thats pretty neat, I wanted to put some fog lights or aux lights in anyway.

I think the issue is I'm missing the trailer relays then. Your 2wd has the front box empty and the rearward box with relays?




Red arrow has 2 relays in box, green arrow box has 2 relay slots but no relays

 

My 2WD does not have a front box, just the bracket where it would be.
Does your truck have ESOF, 4X4 with a switch on the dash?




And those 4 wires hanging off the harness right behind the power distribution box are the other end of those wires. If you can still read the harness label it will say "customer access".

 

Yes, it has the shift on the fly 4X4.

Ill have to get a couple relays and see if that fixes it.

 

So plugged 2 relays in there and still nothing. Plugged a trailer in to see if maybe that was an issue, nothing. Still no power going to the TBC through the connector.

Does it need to be a special relay? Couldnt find a listing at the parts store so just have some multipurpose relays in there, should at least power it up I would think. Standard RY116

 

Turns out I'm retarded and cant read a fuse diagram. Fuse #28 was missing, I had the diagram upside down or something, I don't know.

I swapped in a different 30a Maxi and it powered the TBC right up.

 

Unplug the Tekonsha adapter from the truck's trailer brake controller connector and check to see if it has power for the black wire. It should be energized all the time whether or not the key is on or a trailer is connected or not. If the pin for the black wire on the truck side of the connector has power, check the Tekonsha adapter connector to be certain it is wired correctly to match your truck's trailer brake controller connector. You need power on the left pin top row of the truck side connector.

If no power there at the truck side of the TBC connector then there is a bad wire between there and the fuse. Or someone may have at some point in the last 18 years redirected that circuit for something else like a audio amp or alarm.

 

Nevermind, editing that last post because my TBC was wired to a different plug. The wire colors in your picture appear to be correct.
*edit again* I guess you fixed while I was busy posting all the wrong info. Glad you got it going.

 

Check to be sure that 30A maxi fuse #16 is installed for the trailer tow battery charge circuit. That one and #28 are usually left out if there has never been a trailer brake controller connected.

 

Yep, both were missing.

Thanks for all your help

 

Even a blind squirrel finds a nut once in a while.