Trailer Brake Harness

[adamsanders]

I have a 91 F250 with a factory trailer brake harness that is giving me problems. The red/green wire is not giving me 12V like it should when the brake pedal is pressed. The lights work though and the green wire that runs to the switch in the actual pedal gets a switched 12V. Does anyone know where the red/green wire in this connector picks up the switched signal? It looks like it runs out of the firewall and gets bundled into a harness and heads to the back of truck. It definitely should have a 12V switched signal though. Thanks.

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[chillman88]

That red/green wire I believe is supposed to be tied into the lights somehow so your trailer brake lights activate when you manually apply them using the lever on the controller. I'm not sure how because I never bothered to hook it up. The other two are the ones you need. Blue goes to the trailer brakes and the other one is power to the controller.

When these trucks came out hydraulic controllers were the standard. You didn't need a switched wire because the controller was tied directly into a brake line. If you have a modern electronic controller you will need to tap into the brake switch yourself.

 

[adamsanders]

So this red/green wire was never supposed to have a “incoming” signal, but rather an output signal from the controller? The controller I'm replacing was a Voyager from 1993 which was electric and required a 12V switched signal as well.

 

[chillman88]

So this red/green wire was never supposed to have a “incoming” signal

Best I can tell. I chased it on mine figuring the same as you and sure enough its out back in the trailer harness.

Maybe someone with an EVTM can tell otherwise but that's been my findings.

 

[chillman88]

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This is for an 86 but I believe they are the same. Might have different wire colors though.

 

[Cubey]

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[adamsanders]

Thanks for the diagrams! Looks like our assumptions were correct. I just tapped into the switch on the pedal and it works just fine.