The Brake Warning Light on my 77 has 2 wires to the bulb, a pink going to the center of the socket and a tan to the outside of the bulb socket (normally ground).The tan wire goes to emergency brake handle (warning when the emergency brake is on) and to the center switch on the brake proportioning/distribution block (Warning when the brakes do not have enough fluid to function).

The Brake warning light also lights (tests that the bulb functions) when starting the engine.

Can anyone explain how it functions? The closest I've been able to come is that the bulb gets current from the starter switch and the current flows through the bulb, and the light comes on whenever the switch in either the brake proportioning or emergency brake closes, giving the current a path and lighting the bulb.

What I cannot get my head around is how this bulb performs its self test when starting the engine and then goes out. If the current is momentarily provided by the starter circuit, where does it ground to, assuming that neither the emergency brake is engaged OR that the brake hydraulics are low on fluid? OR, conversely, where does the system get the current from when the start system is NOT engaged in order to light the warning light if the emergency brake is applied or the system is low on fluid.

ANY HELP WOULD BE GREATLY APPRECIATED!!!!

 

On my 73 I am pretty sure the brake switch and proportioning valve switch supply ground to the lamp when engaged so that would mean the positive is the pink wire you speak of. Therefore there is probaly ground from the igntion switch on statup to the tan which branches out on mine to test during startup

 

Looks like there is a grounding switch incorporated in the ignition switch that grounds the light when in the start position.

 

THANK YOU!! You've been a great help.

 

nice work

 

I believe that the pink wire just powers the bulb when the ignition switch is turned ON, for the dash bulb 'test' prior to starting the engine. But, that warning light will come on if either of two faults is detected:

1. The emergency brake is left engaged with running engine;

2. The brake fluid distribution block has detected that one half of the brake system (front OR rear) is no longer functional.

 

SO I am guessing that your only concern was that the brake light was coming on in the START mode of the ignition switch....and the light does go off and is not coming on....correct???

DUB

 

DUB,

Correct! I had figured out how the rest of the circuit functions, but the tan wire being grounded in the ignition switch when in the start position escaped me.

Thank you everyone for your help!

Tom