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Just got done putting a brand new main engine compartment harness in the Shelby and connected everything. Everything works except the brake warning light. Since the MC has no fluid in it, it should trigger the light right? It didn't. So I disconnected the harnness from the switch on the porportioning valve and it still didn't come on. Check the bulb in the dash and it's good. Tried to use a VOM to see if there is current going to the switch and got all kinds of funky readings. Anybody out there got any ideas?
 

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The switch is activated when one side of the brake distribution block has pressure and one side doesn't.
In the middle of the distribution block, there's a plunger which can slide to one side or the other. Normally
it's in the middle and when you screw in the brake warning switch, the pin of the switch is depressed
and the switch goes open and the light stays off. If you lose pressure in the front or rear half of the system,
the plunger is forced to one side by the pressurized half of the system. This allows the in the switch pin
to drop down and that closes the switch which illuminates the brake light.

If you leave the switch connected to the harness, and remove it from the distribution block, it should light the
lamp. Then you can push in the pin on the switch and confirm that the lamp goes off.
 
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