No Brake Lights!

[bruss01]

Quick question: I have the shop manuals but I am having a hard time translating the circuit diagram in the book into actual wires and components on the truck.

My 1978 Scout terra pickup has passed it's emissions test after a carb rebuild and tune-up. Hooray! Now to start in on those pesky little issues that impair road safety and draw unwanted attention (such as flashing lights in the rear-view mirror, and no I'm not talking about a disco ball!).

A previous owner had some kind of do-hicky installed under the dash. It had a brake line running to it, so I'm guessing it was for trailer brakes or something? Anyway, I had to rebuild the entire brake system, and I don't know or care what this gizmo is or does... If I need trailer lights I can just tap into the lines in the back - right? - which makes me wonder why the prev owner didn't do that instead of tapping into a brake line. The brake line to the gizmo is disconnected and I am going to finish removing it asap.

Anyway - I am doing a safety inspection and the brake lights do not seem to work when the brake pedal is pressed. There is an electrical connection on the proportioning valve - is this the switch where the signal originates? I am afraid the prev owner May have played slice-n-dice with the under dash wiring - oh goody! Not!!

Can anyone offer some tips on how to go about troubleshooting the brake lights?

Eta: it looks like there is a switch up under the dash with a little pushbutton that rides the brake pedal... This looks like the one I was looking for.

 

[Michael Mayben]

quick question: I have the shop manuals but I am having a hard time translating the circuit diagram in the book into actual wires and components on the truck.

My 1978 Scout terra pickup has passed it's emissions test after a carb rebuild and tune-up. Hooray! Now to start in on those pesky little issues that impair road safety and draw unwanted attention (such as flashing lights in the rear-view mirror, and no I'm not talking about a disco ball!).

A previous owner had some kind of do-hicky installed under the dash. It had a brake line running to it, so I'm guessing it was for trailer brakes or something? Anyway, I had to rebuild the entire brake system, and I don't know or care what this gizmo is or does... If I need trailer lights I can just tap into the lines in the back - right? - which makes me wonder why the prev owner didn't do that instead of tapping into a brake line. The brake line to the gizmo is disconnected and I am going to finish removing it asap.

Anyway - I am doing a safety inspection and the brake lights do not seem to work when the brake pedal is pressed. There is an electrical connection on the proportioning valve - is this the switch where the signal originates? I am afraid the prev owner May have played slice-n-dice with the under dash wiring - oh goody! Not!!

Can anyone offer some tips on how to go about troubleshooting the brake lights?

Eta: it looks like there is a switch up under the dash with a little pushbutton that rides the brake pedal... This looks like the one I was looking for.

You are describing an old skool trailer bake control that tee'd off the hydraulic vehicle service brake circuit. It was used in conjunction with a large mult-segment resistor block under the hood and used to adjust the trailer brake action through the controller.

This type brake controller (kelsey hayes) is very common on ihc-produced vehicles and was both a line-install option and a dealer-install item. Trailer/hitch shops also installed 'em.

Full electronic brake controllers have replaced those on modern vehicles and are far easier to both install and adjust. Those have nothing to do with trailer lights. Trailer light harnesses are wired into the main vehicle harness at the rear of the vehicle.

Beginning around 1966 IH changed from a pressure switch in the hydraulic circuit to control brake light function, to a momentary contact mechanical switch activated by the brake pedal. That switch is adjustable and rarely malfunctions...but it can have corroded internal contacts. They are not a specialty item and any decent auto supply will have a similar witch that can be mounted very easily.

The switch in the proportioning valve controls the brake warning lamp on the dash and has nothing to do with the brake light system either. That switch is designed to close if a loss of hydraulic pressure is ever sensed in either the front or rear hydraulic brake circuits. That in turn lights the light on the dash as a warning. Some (not all) ihc vehicles also have a switch on the parking brake control that utilizes the brake warning lamp circuit also, that means when the parking brake is engaged, the lamp is turned on.

 

[RobertC]

There is an electrical connection on the proportioning valve - is this the switch where the signal originates? .

That should "connect" to the brake warning light indicator in the dash...

Eta: it looks like there is a switch up under the dash with a little pushbutton that rides the brake pedal... This looks like the one I was looking for.

Yes, it is "adjustable" - threaded... You might want to check that the "push button" comes all the way out when the brake pedal is pressed. Before finding a new one...

Also, might want to check the fuse...

 

[bruss01]

Thanks guys!!

Mike, once again you are a font of knowledge. That trailer brake was a kn, aftermarket by the looks of the wiring under the dash.

It turned out to be the switch on the pedal, bad bad bad.

A quick run to kragen for a switch off the shelf was all that was needed. Now, I have brake lights again!