[undy]

Bruce,

I know you said you'd checked your alternator output before but your car's the same vintage as mine. LSC's electrical systems, although faily well thought and installed, were (are?) somewhat anemic. For example, the wire from the alternator output heading back towards the battery is only #10, not sufficient to feed the battery that feeds our "everything's electric" Cobras. This is especially true with what everyone uses, March's under drive pulleys. My electrical problems, although more pronounced than yours, had a major impact on my gauges as yours did. Since my modification the gauges remain stable under all electrical load conditions. With the lights on, fan running and radio blasting I'm supplying the fan (and the entire system) with 14.2 volts.

Electric pressure/temperature gauge readings, simply stated, are the product of a variable resistance to ground sending unit at a fixed voltage (hopefully) at a given temperature/pressure. If you change the voltage as well as the temp/press you'll change the gauge reading. Some of the older factory installed systems utilized dedicated voltage regulators/limiters for their pressure and temperature gauges. The Brits were famous for that... courtesy of Lucas, God of Darkness...