Diagram for a DIY 939 series warning light/buzzer control box

[TexAndy]

Air switches shown at top left, normally open.
Air switch light just to the right of that.
Parking brake switch to the right of that.
Parking brake light to the right of that.

At the very bottom is the normally open ignition switch.

Relays are shown with coil side on the left, load side on the right.

Buzzer is the swirly thing in the middle.

I HAVE NOT TESTED THIS. Use at your own risk. I came up with this literally in like half an hour of thinking about how the system probably works and then working out in my brain how to replicate it.

This will require cutting your wiring harness at the cannon plug. You will have to splice power from the wire coming from the ignition switch and cut and extend the wire coming from the air switches and the wire coming from the parking brake switch. All these wires are shown and denominated with a number in the TM wiring schematic.

This is what I plan to do in lieu of ordering a NOS control module. From what I can tell, a fair number of those are dead on arrival, too. I'm only posting this because a few people have asked me about it, so rather than keep typing the same thing to different people, I'll just send a link here.

The only difference in operation for my diagram, is that the buzzer will only sound for low air. NOT for parking brake engaged (which I think is kind of stupid).

If anyone sees an error or a way it could be made better, please speak up. I have NO formal electronics training.

Total cost should be under 10 bucks, including a project box.

Again, use at your own risk.