fuel guage not reading... how do i test?

[dbaldie]

i've got an 82, with the digital dash gauges... how can i test the sending unit in the tank to see if it's working ok? alternatively, how do i test the gauge in the instrument cluster? all the other gauges are working as they ought to, so it's not a fuse issue.

looking over the wiring diagrams, it's not even clear if there's juice running to the sending unit, or what. when i test it with a trouble light, all three wires in the sending unit show continuity to ground, but none has "live power" in it.

my gauge always reads at "empty", with the "low fuel" light "on"... i usually just reset the trip odometer when ifill up, then fill up again at around 250 miles, but face it, this is a pain in the arse!

any help would be appreciated.

[Jeeves]

I couldn't tell you much about the Mk2 unit, but here's the old SOGI tip for repairing the sending unit on the Mk3..

http://www.supras.com/06/techcenter/display.php?QID=47

[CRE]

Most fuel gauges use three wires: 12v, ground and sensor. The sensor is usually a ground signal.

To test, you need to determine which input is which on the back of the gauge and then ground the sensor line. The gauge should go to full if memory serves correctly. Putting resistance between the ground on the sensor line and the gauge should move the needle to a position below full. If grounding the sensor line completely moves the needle to the empty location try adding some resistance and see if the needle moves up (I may have the signal orientation backward).