Calling wiring gurus?

[farmall400]

Any wiring guru's here? Or just a wiring diagram.

No brake/signal lights on a 79 C10. Tail lights and reverse lights work fine. No power at the light sockets. Sometimes I have power at the T in the harness (where it T's off to the taillights). Sometimes there is power at the firewall (where the wires go back on the frame) but when there's power there the brake or signal lights won't turn on. I don't have a tester to check the voltage in the circuit.

Is there a switch or common connector that the brakes and signal flashers run through to before current leaves the dash area?

I live on the boondocks, all I have is a test light and an incomplete wiring diagram found on this site.

Thanks!