brian" <brdelab@hotmail.com> wrote:
>I am having a bit of a problem with my fuel gauge reading correctly or at
>all. It started a little bit ago. When I would start her up (1971 IIA 88)
>the gauge would not initially read. After traveling around for a bit, she
>would start reading a fuel level. This, however, would vary from reading a
>quarter tank remaining to as high as half a tank remaining. Currently, she
>reads nothing. When I put the test lamp on the harness that connects to the
>fuel sender, the gauge registers a reading. When I test lamp to the back of
>the fuel gauge where the green and black wire connects to, I get a pulsing
>light and the gauge registers.
>Is there a way for me to test if the sending unit is faulty or if the gauge
>is suspect?
A test light will register a pulsing light. Consider the current path:
first the 'lectricity goes to the instrument voltage stabilizer inside the
dash, then to the temp and fuel gauges, and from each to the sending units
and thence to ground. The fuel tank sender is some resistive wire and a
'wiper' for a contact, so the gauge functions more like an ohm meter than a
volt meter.
The pulses are created by the instrument stabilizer, a fine product of
generations of Lucas electrical engineering. The only way (at the time) to
get the stabilized 10.3 volts that the system needs was by use of a
bi-metalic strip: it opens/closes, creating the pulses that the light
'sees' but the relatively slow movement of the needles in the guages do not.
So consider the current path and try to clean up all the contacts,
especially the ones on the top of the fuel tank. I've had a fuel tank
sender go bad with no apparent faults. Pulled the bloody thing apart -
wire had continuity and the shined-up wiper arm made contact, but it still
didn't work.
Try not to think about the fact that you have a sliding electrical contact
and resistive wire in the vapor-rich environment at the top of the tank. ;-)
Cheers
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