Triumph Repair: 1978 spitfire 1500 electrical, voltage drop test, voltage stablizer

Question
no   o fuel/temp gauge..have replaced voltage stablizer (no change)have seen both gauges go right over after groundin.g hot wires,so i assume they are o.k.what else can i check ,iassume the grounds, but where do i start,or do i use a new ground, if yes, where/

Answer
Hi Bernie,

On all of the electrical gauges we used a preliminary test and that was to turn on the key to Ignition and have someone watch the gauge while you remove the wire off of the sending unit. You should see the needle deflect all the way in one direction and then touch the wire to ground and the needle should deflect all the way in the opposite direction. (don't leave it grounded long as that can damage a gauge)

That test checks the power to the gauge, the gauge and the wire to the sending unit. But is only a rough preliminary test. If it did not do that then we would first check battery voltage (12v +) and start the engine and set the RPM at 1500 RPM and check battery voltage again. It should be (13.8v to 14.5v) but no more.

Then we would check the voltage stablizer output voltage (10v) (don't skip this because you just replaced it.

To correctly test grounds to a load (gauge in this case). Put you your (+) test lead of your voltmeter (set on low voltage) on the case of the meter. Then put the (-) test lead on the (-) post (not cable end) of the battery. Turn the Ignition on and watch the voltmeter. If there is a resistance in the whole ground circuit the power to work the gauge will seek a new ground in which case is you voltmeter and thus you will read a small voltage. In the case of a gauge we don't know how much voltage is too much so you can test it simply by leaving your voltmeter connected and take a heavy gauge wire (12 ga) and touch one end to the gauge case and the other end to the negative post (not cable end) of the battery and see if the car gauge reads correctly and the Voltmeter goes to zero or close to it. This is called a "voltage drop test" and can be done on the positive side of any load also. But the load must be active at the time of the test.

With both gauges affected you for sure have either a problem with the 10v power or the above ground problem. A simple test of the alternator voltage test is to check the gauge reading with the key just on and with the engine running.

Let me know,

Howard