Brian,

Some folks say it makes no diff on the 6v to 12v swap with the fuel gauge...some folks say it's instant death. There are lots of posts outlining the test procedure for gauge and sender. If you search and find them, have your buddy run these little tests and he can probably verify the health of the gauge.

His purchase at NAPA should have been for a small resistor device to knock the 12 volts down to 6 volts for the gauge or any other device he was keeping at the original voltage. If he installed this dropping resistor after the fact, it might be too late if the gauge did indeed go to the happy hunting ground.

Stuart