Question about 1991 Ford F150

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

Do you know of a source for step-by-step wiring instructions (preferably with diagrams/photos) for installing a 7-pin wiring harness on this vehicle?
i've completed the installation on the trailer in accordance with the US color coding, but am a bit overwhelmed with how to hook up the pickup-side of the equasion to electric brakes, back-up lights, and charging the RV battery with the pickup alternator.
Serious Thanks,
torr

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I believe you can look up the manufacturer of the trailer plug kit and find the wiring diagram there. On alot of the trailer plug kits, they have pics and diagrams in the package. The 7 pin plug (truck side) is available with the pig tail set up that plugs directly into the wiring harness for the lights. Then all you would have to worry about is the 2 wires for the electric brakes.

Posted on Nov 30, 2008

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Have no power out of the trailer plug 4or 7 prong,where should i look for the trouble?


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.

Mar 16, 2011 | 2004 Ford F150

1 Answer

Can't get the back up light to burn, the fuse & bulbs aare good so it must be the switch, Where is it located???


Might want to verify the switch operation by checking the 7 pin trailer tow adapter for the reverse circuit. This is a standard 7 pin RV type plug
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The "reverse switch" is called the DTR ( Digital Transmission Range ) Sensor, and it is mounted on the side of the transmission. This also contains the contact for only starting the truck in park or neutral, so if that works correctly, I would take a SWAG that the reverse section of it is OK ( but that is a SWAG ).

You can check the 7 pin, if that reverse works, the DTR is fine and the issue could be at the rear of the truck with the splice ( which the trailer tow adapter also goes through ).
You need to drop the spare tire to get to the connector, it is a large multi pin connector, reverse is the Black w/ pink stripe wire.

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2 Answers

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

the 7 pin RV plug itself

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The 2005 trailer tow adapter wire diagrams
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Oct 23, 2010 | 2004 Ford F150

1 Answer

06 f150 wiring trouble


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

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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.
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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 )
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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---
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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...

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