Classic/Antique Car Repair: 1970 mustang gauges, oil pressure gauge, wiring error

Question
the temperature gauge and oil pressure gauge both peg to max. disconnecting them from the sender makes them go back down

Answer
There is either a wiring error in the gauge cluster or your instrument voltage regulator has failed. (This is NOT the same thing as the Voltage Regulator that controls the battery charging.)

If someone has been fiddling with the wires, get a wiring diagram and trace all the wires on the gauges, paying special attention to the instrument regulator hook up, and the grounding of that item. If you can't find anything wrong, the instrument regulator may have failed - NAPA still stocks these; just buy a new one and change it.

If you want to, you can test this yourself by taking a test light and putting it on the end of the wire that goes out to the  temp sender (disconnect it from the sender and probe the end of the wire).  If the regulator is working right, when you turn the key on, you should see a pulsating light on your tester, or if you use a meter, you should see a jump in voltage every second or so. The meter won't be quick enough to give you a sensible reading, but if you see the pulsation, the regulator is OK

Dick