I have a 55 Ford converted to 12 volts.  All gauges and senders are original.  Gas gauge reading corrrect.  The problem is the temperature gauge reads almost all the way over to Hot but engine is not hot.  Prior to installation, temp gauge tested correct using 1.5 Volt battery.  The temperature sender is fairly new but had a high reading prior to converting to 12 volts.  Any suggestions?  Thanks, 

Gary