I was investigating the trailer wiring on my 1995 F150 today and realized that I have no idea what's going on back there. I'm familiar with the 4-pin connector, and have seen 7-pin connectors. What's all this extra stuff?

noddaz GRM+ Memberand UltraDork
4/12/20 6:28 p.m.

It looks like you have an adaptor to allow a 4 pin trailer harness to be used without splicing into the factory harness.  Good thing there.  As for the round 4 pin connector, no idea.

karplus2 GRM+ Memberand New Reader
4/12/20 6:51 p.m.

In reply to noddaz :

My 94 Explorer has a secondary harness that plugs in to the factory harness that ends behind the bumper. That way there is nothing visible in the back when not towing. I assume this is something similar. I can try to look at it later tonight to see if it is similar to the pics you posted.

bentwrench SuperDork
4/12/20 11:29 p.m.


That looks like a "T" adapter that allows for a flat 4 pin trailer plug. 

And the flat 4 wire cable has been cut.

The loose connector may be for Lic Plate lights?

thatsnowinnebago (Forum Supporter)
thatsnowinnebago (Forum Supporter) GRM+ Memberand UltraDork
4/13/20 12:21 a.m.

In reply to bentwrench :

So this t-adaptor essentially splices into the factory tail lights? Is that right?

I've never checked the license plate lights for functionality, but I will now. Thanks!

karplus2 GRM+ Memberand Reader
4/13/20 8:45 p.m.

This is the plug I was thinking of on my Explorer. Not the same. I am of no use.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
4/14/20 8:20 a.m.

Ford is really good about adding all the extra adapters for things you'll never need, but terrible about adding adapters for things you might actually want.

I can't speak specifically about what they are exactly, but yes, the last one you pictures looks like the factory trailer wiring splice point for the aftermarket plug-in harness.

The other ones could be for optional emergency lights, or part of a harness that was only used for cab and chassis models, or doomsday prep.  They add all that useless crap, but if you want to add cruise control, power windows, or power seats, the wiring isn't there.  You have to buy the whole cruise control harness and tear apart the dash, wire it into your fuse panel, and rebuild half of the truck.

I was thinking about adding cruise on my older Ranger.  It would have required a complete teardown and rebuild of the steering column, partial dash disassembly, and knocking out a plug in a spot on the firewall that required removing the HVAC.

The easiest way to find out what they are is to either find a shop manual or google wiring diagrams for your truck.

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