Yo Tuske

I did the conversion 15 years ago... so I dont remember any real problems. Both my temp sender (idiot light switch) and oil sender switch were replaced with variable single wire sending units from the local auto part store. Both work as expected. you can test the circuit by grounding the connections. Oil pressure should read low when grounded, high when circuit is open.. Temp should go high when grounded, low when open.

ON the wiring diagrams I do not see any second wire to the temperature sender...... mine does not have it. my SWAG is the car has A/C?

I would not worry about the voltage unless the car does not charge. many cars do not charge at idle and the ignition and other things are loads.

NOt much help, but I thought someone should say something.....

mark