Installing a 7-pin trailer towing recptical on a 1991 Ford F150.

https://www.176iot.com/
4 wire or 6 wire or 7 wire plug?

Not sure which part you mean no power.

For the New Body style 2004 ( not a Heritage or Lightning model )

If both Stop / Turn pins & the parking lamps, might want to check the ground pin to make sure it is good ( or what you are using for ground on the test light / meter ).

The trailer tow parking lamp circuit is fuse #10 to the parking lamp relay

The stop / turn circuits also have fuses on each one, Fuse #36 & Fuse # 42 ( R & L ).

The 7 pin has fuses for the battery charge pin ( hot in run position ) and the reverse circuit ( hot in run & when in reverse ), Reverse is also fuse # 10 to the trailer tow reversing lamp relay & the battery charge pin is fuse # 106 to the trailer tow battery charge relay.

Could be all the fuses are blown, or what you are using for ground on the meter / test light is not a good ground.

I am guessing you mean the 7 pin trailer tow adapter.

the 7 pin RV plug itself



The 2005 trailer tow adapter wire diagrams

Check Fuses # 36 & 42, these are the fuses for the trailer tow adapter ( separated from the trucks.

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

I would check the bulbs, remove them and test with a DC power source ( DC power adapter to 2 wires Pos + Neg )

Fuse #14 has the reverse lamps on it, as well as the Day Time Running Lamps ( DRL ) relay coil, the shift interlock ( would not be able to take the truck out of park, while it was running ), and some other items I am missing at the moment.

If you cannot make the test harness to a DC power outlet, you can block the wheels ( at least 2 - front and rear ) on a level surface, turn the key to the run position ( do not start ) and place the truck in reverse, and check the bulb socket with a meter or test light to check for power.
If it is installed, you can also check the Trailer Tow adapter reverse circuit as well ( this is relay is triggered by the reverse circuit ).

If you do not have power at either ( don't forget to check for corrosion on the trailer tow 7 pin adapter ) this would be the DTR ( Digital Transmission Range ) sensor on the side of the automatic transmissions.

Have you used an aux backup lamp on the truck's reverse circuit ? ( not the trailer tow 7 pin adapter )
The DTR sensor and reverse circuit does not like 1 AMP additional load on it ( the lights will not burn at full brightness ) and if an additional load has been on them, the DTR sensor at the reverse contacts could be carbon'd up.

u must install the fuses for the system in he underhood heavy duty fuse box, it will be marked trailer tow

try http://www.etrailer.com/faq-wiring.aspx. This should help. Mike

I take it the blinkers and brake lights work ok when not hooked up to the trailer? If yes, then the wiring to the tow hitch is not hooked up correctly. How many wires to trailer pig tail connection? U can have up to 7 depending on what you tow. Check to make sure these wires are hooked up from the truck to tow plug correctly: 7 wired---
brown-Rt turn and brake light, yellow-backup, white-ground, blue-electric brake, green-tail running lights, black-battery charger, red-left turn signal and brake light. Let me know if u have something other than 7 wire, I'll get the wiring color and source info for u.

My 2004 f150 has the factory tow package. It has a fuse for the trailer running lights seperate from the truck running light fuse.
Check, you may have the same set up...