Re: 2 Gauges just zero'd....

["ROSS BLAIR" <bigbad69@xxxxxxxxx>]

snip...
There's a gizzy on the circuit
board the looks like a piece of cardboard wrapped in electrical tape, it's
not the voltage regulator but one of pins going to this device broke on my
68 and caused the gauges to go dead.
...snip

This is a choke to suppress static on the radio. It can be substituted with a short length of wire if it is suspected to be bad. The worst that can happen is noise in the radio.

If the regulator is separate from the temp gauge, it will be a metal can with 3 spade terminals on it mounted to the instrument panel circuit board. One terminal is 12V (battery) , one is 0V (chassis) and one is the regulated output. This regulator is a bi-metalic spring much like the choke pull-off. The current through the regulator heats the spring and causes it to bend. When it bends far enough, the contact points open and the circuit is broken. The spring then cools, the contacts close, and current flows again. The cycle then repeats. This happens about twice a second. If you probe with a digital voltmeter, you will see the voltage jump and drop repeatedly. Because of the frequency, you will not usually see a 12V reading or a 0V reading, which is what is really happening.

These regulators power only the temp and fuel gauge, so when both fail at once, it is a good indication that the regulator circuit is the cause of the failure. The choke mentioned above may or may not be present. Check that there is 12V to the regulator, and make sure the circuit has a good connection to chassis, then check that the regulator is functioning. The pulsating voltage should be present at both the fuel and temp gauge.

If 12V or ground is not present, there may be problems with the circuit board. If both are present, but the regulator output is not pulsating, then the regulator is probably bad.

Or, if you're the type who buys lottery tickets, then forget the tests, simply get another regulator, slam it in, and cross your fingers. :)

Ross Blair
69 BBO Javelin 390
Ottawa, Ont.

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