Quote:

...The Painless tech advised that it would be dangerous to continue to use the gauge, as he stated it was 40 year old technology...




More like 140-year old technology, and a technology that's still used today. It sounds like that "tech" was trying to sell you something. The problem is tired old riveted connections and ammeters that put out a lot more than the 40-60 amps the gauges were designed for. Swapping in a WT or OP gauge could work but getting it to read accurate numbers would be tough. If all you needed to know is whether you were above or below 12-14 volts then it wouldn't be that tough. The gauges are usually about 12-15 ohms while the sending units are about the same at minimum resistance and around 80 ohms at maximum resistance. If I remember right the sending units are around 30 ohms at mid-gauge and if we assume the IVR output is 5 volts then the gauge would see about 1.7volts at mid gauge. At maximum reading the voltage across the gauge would be about 2.5volts and this is then about the maximum you should put on the gauge based on the assumptions above. Now all you have to do is design a voltage divider to generate about 2.5@15 volts and/or 1.7@12.5volts. It looks like 6 or 7:1 will do. Of course some testing will be necessary. I've found the IVR to actually put out over 6 volts effectively in back to back comparison with a solid-state regulator.