Ian:
The fuel gauge is thermal, so if it reads full, the gauge itself
is working (I am assuming that the gauge reads empty when you turn off
the key). What this means is that the gauge responds to heat from a
current passing through the gauge. The gauge works this way so that it
is damped, responding slowly to changes in the current passing through
it. This prevents the fuel gauge from bouncing up and down every time
the car hits a bump and fuel in the tank sloshes around.
The temp and fuel instruments work in this manner. This is why
polarity of the gauges doesn't matter when connecting the wires, as the
gauges only care about the heat generated by current, not the direction.
This is also why the voltage regulator can be the cheesy intermittent
style that they are. If the gauges used voltage or current to register,
they would pulse every time the voltage regulator did its thing. Since
they use heat and register changes very slowly, the voltage regulator
can pump the voltage up and down as much as it wants, as long as the
average is around 10 volts, everyone is happy.
If your voltage regulator is bad, your temp gauge should also be
reading high as it is identical in configuration to the fuel gauge. If
your temp gauge appears to be working normally, then the voltage
regulator is unlikely to be the culprit.
After replacing the regulator if fuel gauge is still
misbehaving, you have two items left; a short or a bad sender.
Disconnect both wires to the sender and watch the gauge. It should
return to empty gradually over several seconds. If it continues to
register, you have a short somewhere between the gauge and the sender,
if not then the sender is bad.
If you have a short, disconnect the rear wiring harness (the
plug is behind the left side kick panel under the dash). If your gauge
still reads full, the short is in the dash somewhere. If it now reads
empty, it is between the plug and the sender.
Let's hope it is a bad sender. They are easy to isolate and
repair.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Ian Breyer
Sent: June 21, 2005 9:51 PM
To: 6pack@autox.team.net
Subject: trunk light switch & guages
A few questions for the list:
<snip>
3) The above questions came to mind while replacing my
fuel sending unit. After removing the old sending
unit, fuel was discovered inside the float. I felt
confident that this was the cause of my fuel guage
always reading full...unfortunately the problem was
not solved. (Upon reflection I suppose that fuel in
the float would probably make it read empty all the
time.)
I just ordered a new voltage stabiliser. Comments
would be welcome. I am guessing if that doesn't solve
things next step would be the guage itself.
Thanks,
Ian B
72 TR6
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