QuestionIn September I bought my first car, a 1959 Ford Custom 300. The electrical system appears to work well excluding the courtesy dome light which never turns on. I don't believe the door switches are broken and the light bulb is good. If you have any suggestions as to what could be causing this problem, I would greatly appreciate your help.
Take care,
Riel
AnswerThere are a long list of possibilities, all I can do is help you to track them down, one by one.
You probably know this, but just in case, the bulb always has 12 volts on one terminal, and will light if anything grounds the other terminal. This is done by either of the door switches, or by the headlight switch, if the knob is turned all the way CCW. If you haven't tried the latter yet, do that - if that makes the light come on, you know there is 12 volts at the bulb, so the problem must be in the door switches.
The door switches on old cars usually develop dirty contacts, and can only be fixed by taking them apart to clean the contacts. To verify that this is the problem, remove a door switch from it's mounting and manualy ground the wire connected to the backside of the switch. If this makes the dome light come on, you know the problem is in the switch - replace it or take it apart and clean it, and make sure the mounting is clean so that the ground has continuity.
If turning the headlight switch knob to the left all the way DOESN'T make the dome light come on, you'll have to see if there is 12 volts at the light fixture.
First, you need to obtain a test light - or make one if you are handy. All it takes is a small 12 volt light bulb, a #1895 is a good choice, and two wires with a clip lead on one end of each. Solder one wire to the outer copper shell, and the other wire to the center contact of the bulb. Or, you can buy a professionally made test light at your local auto parts store for about $5.
Now, anytime you contact a point with voltage on it, the bulb will light - you will use this often in troubleshooting this and other electrical problems.
Next, take the bulb out of the dome light fixture and verify that there is 12 volts on one of the two wires that feed that fixture. If there is, then the problem is lack of ground to the other wire on the fixture.
Lack of 12 volts at the fixture points at a blown fuse or a bad wire connection in the circuit - beyond that I cannot help you, it is pure detective work from here on. Find the wire where it runs up to the roof and trace it back to the source of 12 volts - it is possible that the wire is disconnected or broken, perhaps in a hidden location.
Good luck - you'll need it!
Dick
