Old Brake Controller ?

[69C20CUSTOM]

On my 1986 Suburban it came with this old Brake controller.
Ive used them before on my diesel but nothing like this one.
I dont know how it works.
Its got a few wires, a brake line that runs to it right from master cylinder.
But a big ? is it only has a flat 4 trailer wire connecter out back.
Here are a few pics.

Can some one tell me how it works.
Thanks

[blakeduren]

It runs of the pressure of the M/C.
The wires should be:
Red: power to unit
Black: ground to unit
Blue: Brake wire to pins out back

That red/blue wires I see in your engine compartment probably run all the way to the back of the truck some where. The Red wire in that pair is 12v power to a 6 or 7 pin trailer hook up.

I took out a similar setup out of my suburban when I got it to put a new Prodigy Unit in.

Fellow K.C. er,
Blake