Re: Changing '55 to Negative Ground System

Posted by HH56 On 2018/9/1 14:05:16

Motors in a stock Packard have separate field and armature coils. The motors are wired internally to always have the same magnetic N-S pole relationship between the field and armature so a polarity swap feeding the motor makes no difference since both field and armature will change at the same time and be affected the same way. To make the motor change direction there would need to be a switching of the coils so typically 4 wires exit the motor. A switch would then be used to change magnetic relationship on either the field or armature while the other stayed the same and thus direction is changed. Packard did this with the the prewar Deluxe heaters and hydraulic windows where a switch made the motor run one direction for defrost or window up and the opposite direction for heat or down. Reversible motors post war have two separate field coils wound in opposite directions for the different magnetic fields needed to change direction but only one field coil is used at a time. The armature is wired so it always keeps the same relationship to the fields. One exception may be the 54 electric seats which I believe have relays to swap the field or armature as was done prewar and the other is the 56 push button shift motor.

If a window or heater motor has been changed to one of todays permanent magnet field type motors then those are definitely polarity sensitive and wires would need to swap. Believe the high torque mini starters also fall into that category as would most likely many of the aftermarket AC units. If any of those have electronic temp and speed controls then it would get even more interesting if there are no reverse polarity safety circuits built into the units.

Packard used both thermal and magnetic type gauges so there is either a heater coil wrapped over a bimetal strip or two opposing magnetic coils --again always in the same relation -- making them move. Those don't care which direction the current flows so not polarity sensitive. Where that would change is if the car uses an instrument voltage regulator to supply the 5v gauge heater voltage and the old heater and bimetal type regulator has been changed to a modern solid state device. Those most definitely do care.