Re: 49 Temp gauge

Posted by HH56 On 2020/10/2 10:26:39

The gauges in the 48-50 models are somewhat unique for Packard in that they are the only years that use a pulsing on/off action from the senders instead of a straight resistance change as was provided for all other years that had electric gauges. A heater around a bimetal strip in the senders is in series with a heater around a bimetal in the gauge and gets voltage and current thru the gauge heater. Sender heater starts to heat which wants to move the sender bimetal one direction to close a contact to ground. The fuel sender float, oil pressure or the temperature acts on the bimetal in the opposite direction to oppose the heater. Depending on how strong the variables act on opposing the sender heater the pulses change in length or duration which affects the gauge bimetal so it heats or cools and the needle moves in proportion to the on/off timing of the pulses.

Since the gauge needle does not seem to move, first thing to check is if you have voltage at the gauge. The gauge should be directly tied to the others via some jumper strips so if the other gauges work then if connections are clean and tight 6v should be present. If so MOMENTARILY ground the wire at the sender going to the other gauge terminal and the gauge should start to move toward cold. As soon as you see the needle moving disconnect the ground or turn off the power. If the needle moves, the sender or a bad ground between the sender and the head is the most likely issue. If the needle still does not move, a broken wire or bad connection between the gauge and sender or a burned out gauge is the more likely problem. If the old insulation cracked or fell off and the wire to the sender shorted letting the gauge stay grounded it could have burned out.