I really would not bypass that "proportioning valve." It is put there to
prevent rear wheel lock up under hard braking. First of all, a proportioning
valve cannot turn on a light. That is done by the warning switch which has a
wire attached to the top of it. If disconnecting the wire turns off the
light, you have found the problem. What needs to be done is to center the
shuttle piston in the switch. The shuttle has rear brake pressure on one end
and front brake pressure on the other. It is supposed to tell you when there
is pressure loss in one system and is usually turned on byu someone bleeding
the brakes. Since they are not all the same and I do not know which type you
have, I will suggest several things to try.
1) Tap on it. If it is the self centering type this may fix it.
2) Loosen the screw in switch that the wire is attached to, lightly apply the
brakes, tighten the switch.
3) Have a friend apply the brakes, loosen a bleeder at the front and see if
it blinks, then try the same at the rear. The trick will be to catch the
shuttle in the center of its travel and it can be quite frustrating.
Perhaps someone out there will know which type switch you have and can be
more specific.
Good luck,
Don
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