Message text written by Brian Ruess
>Just what does the big red "brake" indicator light indicate when the
engine
is running? I have no owner's manual (first question -- is there a source
for them, even just a photo copy?). It seems to indicate oil pressure, and
the little green light "oil" in the tach comes on along with it. It does
not come on cold and it turns off with higher rpms when warm. However, my
gauge indicates plenty of oil pressure (30-35 at idle, 80-85 at 3,000) and
the dipstick shows enough oil. Is one of these indicators wrong or do the
lights indicate something else?
<
Brian,
A brief primer on the Brake Warning Light system and the Oil pressure
Warning Light system and how they are interconnected (for a more
comprehensive description I suggest you buy Dan Master's book)
The oil warning light switch is connected to the block of the engine. When
the oil pressure is below the setting of the switch the switch will close
completing the circuit allowing the oil pressure light to glow.
The (new this year) dual circuit braking system includes a special device
that detects a pending failure in one of the braking circuits by detecting
a differential in the pressures in the two circuits. This device, the
Pressure Differential Warning Actuator (PDWA) contains a shuttlecock which
has the pressure from each circuit presented on each end. If both
pressures are equal (or nearly so) the shuttle will remain in it's
position. If a leak occures and one circuit pressure falls off the shuttle
will shift toward the low pressure side and a switch is activated which
completes the circuit for the warning light.
How they are interconnected: One lead of the Brake Warning Light is
connected to +12 and it's other lead is connected to one lead of the Oil
Pressure Warning Light. The other lead of the Oil Pressure Warning Light
is connected to the Oil Pressure Switch. The PDWA switch is connected to
the point where the two bulbs are tied together.
If the PDWA is centered (there has been no brake failure) the two lights
will operate under control of the oil pressure switch with the two bulbs in
series (6 volts on each bulb). This provides a quick way to verify the
brake warning lamp is functional each time you switch the key on before you
start. If the PDWA has experienced an imbalance of pressure (pending
failure) the switch will close causing the brake light to shine brightly
(12 volts) and renders the oil warning light non-funtional.
Now in your case, the lights are coming on at idle because the oil pressure
is falling below the switch point of your oil pressure switch. You say you
have 30 - 35 PSI according to your gauge. So either your oil pressure
switch is switching at too high a pressure (these things should switch in
the 5 - 10 PSI range) or your gauge is reading high. (let's hope for the
former). You may try replacing the oil pressure switch and see if the
symptom goes away. They're pretty cheap.
Good luck
Dave
P.S. Buy Dan's book anyway.
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