QuestionI am having a problem with the electrical system on my 1939 Plymouth P7. The battery is 6 volt, postive ground. When the headlights are on, the headlight switch heats up to the point that you will burn your finger if your touch it. I checked the ground lead from the battery to the frame and found it to be secure. I also checked the leads on the generator. I installed separate ground wires on the tail lights and tightened down the headlight wire connections at the terminals on the inside left fender. The problem is still there. Any suggestions?
AnswerThere is only one thing that can creat heat in an electrical system and that is current flowing through a resistance. The heat you are feeling is caused by an abnormally high amount of either resistance or current in one of the connections to the switch, or within the switch itself, or in the associated circuit breaker.
Remove the switch and associated parts so you can inspect the connecting wires and terminals, and make sure every connection is made by metal to metal contact, with no tarnished contacts or loose connectors. If that doesn't cure the heating problem, disconnect all the wires and disassemble the switch itself (it wasn't made to be taken apart, but you CAN do this, if you are careful not to break off the bent over tabs that hold the phenolic board to the metal body of the switch).
Take careful notes of where everything goes, and go through all the metal to metal contacts inside the switch, cleaning them to bright shiny metal with very fine sandpaper (600 grit) and then remove all traces of the grit.
Also, and before you take it apart, verify that the heat is coming from the switch, or one of the connections. It is possible that the associated circuit breaker, which is probably mounted on the switch, is the culprit. If it is the circuit breaker that is getting hot, replace it - these are available at NAPA. Take in the old one and match it up.
If you have "updated" the headlights to Sealed Beam bulbs, this could be the root cause, as this makes the headlights use much more current than the car was designed for. In this case, you may not be able to solve the problem by cleaning connections - you may have to obtain a "headlight relay" and use it as a remote switching device to turn the headlight bulbs on and off. 6 volt headlight relays are getting hard to find; I have to use them on my Hudson, as I converted to halogen headlight bulbs for the additional light they produce. The relays are noisy but you only hear that when you turn the lights on or hit the dimmer switch. I found a dual circuit 6 volt headlight relay at the local NAPA store. You need a two section relay, or two separate single ones, one for high beams and one for the low beam headlights.
Since the original "square" headlights on the 39 Plymouth are one of the best looking features of the car, if you still have them, I envy you! The 39 Plymouth was one of the first cars I drove - as a teenager in the late 50s.
Good luck with it!
Dick
