Kendall---On your '74, I believe the brake warning light can "come on"
from either of two sources. The first one being if the Pressure
Differential Warning Actuator is tripped off-center. This PDWA is the
"brass valve" with the white nylon switch coming out of it's top. If
this switch is connected and working, the dash light should not come on,
when the two braking systems are in balance. Since your light Doesn't
come on, chances are good that this circuit is OK. Now to your
"no-light"
probability.
The brake warning light, as well as the oil pressure warning light, (in
the tach face) should glow feintly when the ignition key is turned to
the "start" position. This is controlled by the three-pronged pressure
switch coming out of the engine block, (to the bottom left of the
distributor.) When oil pressure is sensed, it opens the circuit and
both of these lights go out. If yours never come on with the key, one
or more of these wires isn't making contact at this switch, OR not
connected to the right terminal. You didn't say whether these lights
used to work and now don't. If you have a wiring diagram for the '74, it
will show you which wire goes where. This switch itself can be tested
with an Ohms meter and compressed air. Usually if they go bad, the dash
light(s) will stay on, rather than not light at all, as you report.
If the wiring diagram isn't clear, write back and I'll decipher it. (I
just went thru this drill after I had this switch out!)
Dick T.
'73
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