6 to 12v conversion.

[JSeery]

The gauges and senders work off of current pulsing, not voltage. But in the Ford manuals they suggest using higher voltages to do testing and warn to only use it for a short period of time. If it was not an issue Ford would not have installed voltage reducers when they switched to 12 volts. I would suspect there is voltage reducer somewhere in the system that is just not easy to see.