Triumph Repair: still no fuel/heat gauge readings, gauge readings, voltage stablizer

Question
retested voltage stablizer.o.k. very dim light with test light at sending unit?ground out gauges, both go way over to right, so i assume gauges are o.k.what can i try now.it is getting frustrating, but i will get there eventually thanks to your help.have not found problem, butwith your help, i am slowly eliminating possible causes..thank you...1978 triumph spitfife 1500...

Answer
A dim light at the sending unit? What did you do that for?

You grounded each gauge individually and the needle went full deflection? Then remove the grounding wire and the needle goes full deflection the other way? Each gauge must be tested by itself.

Did you use a volt meter to test the voltage stabilizer? (10 volts) If you leave stones unturned you will never find the problem. Did you check battery voltage and then check battery voltage with the RPM at 1500? The voltage from the alternator to the battery effects the voltage stabilizer and thus the gauge reading. If you don't have a volt / ohm meter they are inexpensive at stores like Radio Shack.

If the problem is effecting both gauges the same, then you have a wrong voltage being applied or a poor ground on the instruments. The temp gauge sending unit and the tank sending unit are totally different types and unlikely to fail at the same time. I don't have any ohms figures for the test of the temp sending unit but you can use an ohm meter to measure the resistance between the spade and the ground and write that down. Warm up the engine and and check the ohms again and you should see a different reading. This test is with the wire off.

Next if the fuel level is low you can remove the tank sending unit and connect both wires back on to the sending unit and stuff a shop reg in the open hole so that you don't have a spark and turn on the Ignition and hand operate the float lever and watch the gauge. You should be able to make the needle move full and empty by hand.

Don't skip anything.

Let me know,

Howard