TreeSeeker wrote:
Griff,
Wow, I didn't know there were 5vdc gauges. If someone hooked up the positive wire directly, then it would explain the gauge maxing out quickly as the voltage exceeds 5vdc.
Eyeteeth,
So, you just need to measure the voltage at the gauge to see if it exceeds 5vdc when the engine has warmed up. Actually, it should be reading about 2.5vdc when the engine is warmed up (assuming it is a 5vdc gauge).
Anxious to hear what you find.
I suspect the 5VDC gauges are a throwback to the days of 6 volt starters and batteries. It'd be easier for manufacturers to add a instrument voltage regulator rather than replacing two or three gauges. (Or, it was easier than getting the gauge manufacturers to change their production lines.)
Even the aftermarket gauges are still 5VDC ... each one has a resistor or voltage regulator inside the case to allow them to be connected directly to a 12VDC supply.
I recall the days when people were converting 6 volt cars to 12 volts. A lot of people had "issues" with their dash after the conversion. (I used to jump a 12 volt battery to my '47 Willys Overland wagon to start it ... and occasionally had to replace the starter and other parts because of it.)
