1959 1 wire Door Jam Switch

[60eldo]

  Can anyone tell me how this works to turn on the dome light? I know that ground is when you push it in, and have 2 wires makes sense one being power in then 1 wire to the light. But I cant figure out how it works or how to test a switch with only 1 wire.

[Cadman-iac]

That's actually opposite of how it works. The system has power throughout but it's not completed until a door is opened.
With the door open, the switch grounds the circuit and the lights come on. If you have the switch out, take a meter and see if you have voltage on the wire going to the switch without grounding it. This will tell you if your wiring is good, providing that the bulbs are also good. If you now ground the wire to a good clean location, your lights should come on.
If you don't have voltage, your fuse may be bad. You can also just have some corrosion on the fusebox contacts. A vehicle that old is subject to electrical corrosion. I have seen wires that run under the carpet actually corrode in half from getting wet. That also creates an unintentional ground and the lights will come on whenever there's enough moisture to complete the circuit.
The problem is that the wires were connected to each other with a crimped and soldered joint and wrapped up with tape to protect it. But the engineers didn't count on the carpet getting wet.
If you have a problem with the courtesy lights,  you could be taking the car apart looking for the issue. It helps to know how/where the wiring was ran through the car.

Rick

[fishnjim]

Grounds through the switch casing to the door jam.   As above, your just completing the circuit when it pops out. 
If it's not working, it's most likely the switch.   Many replacements available.   Might be repairable but not worth it.   

[60eldo]

  So I just have the switch, no car to test it. Is there any way to test the switch using a battery? This switch is out of a Fleetwood rear door, the front doors have 2 wire switch

[Cadman-iac]

Using a meter, check for continuity between the terminal that the wire goes on to the housing of the switch itself. With the plunger pressed in, there should not be any contact/continuity.  Once the plunger is released, then you should see a contact/continuity.
Hope that helps.

Rick

[60eldo]

  Should I ground the switch

[Eric DeVirgilis CLC# 8621]

The original door switch is three pole and the only "replacements" that I'm aware of are single pole which will not allow the individual switches for map, door courtesy and dome lights to work properly when the ground leads are combined on a single pole switch.

What has probably happened is that the contacts have become arced for one of the circuits. Thankfully the switch can be disassembled and contacts cleaned without too much difficulty. I used wire wheel acid to clean the copper contacts which did a great job of removing the carbon deposits. 

*The switch IS already grounded to the body by design.

[Cadman-iac]

  Should I ground the switch

To answer your question,  if you are testing the switch off of the vehicle with a digital meter, no, it's not necessary to ground it, one of the test leads is acting as the ground,  the other is acting at the wire circuit.  All you are trying to do is see if it has continuity once the plunger is released, IE: the door is opened.
If you are checking it with it still on the car, disconnect the wire and use one lead of the meter in place of the wire and place the other lead on a good ground. If the switch is good, then it should read continuity with the plunger out.

[60eldo]

  OK thanks guys I got it. It works but I didnt use a multi meter.  I have 3 and I dont know how to use one,,LOL  I used a test light, grounded switch on top post of battery and then take test light from power post to wire on side of the switch, light came on then when I pushed in the button , light went off,,,thanks good lesson BTW  I still dont understand how it works when installed. The 1 wire coming to the switch has got to be power,,,but then how does power get out to the dome light

[Cadman-iac]

Power goes from the battery to your fuse, then from there out to each of the bulbs in the circuit,  through the bulb and back through the other wire, the one that you see at the switch.  When that wire is grounded when you open the door, it completes the circuit and the light come on.
Hope that explains it well enough. Good idea with the test light. I didn't realize you had a problem with the meter.

Rick

[Eric DeVirgilis CLC# 8621]

   I used a test light, grounded switch on top post of battery and then take test light from power post to wire on side of the switch, light came on then when I pushed in the button

Light should go out when plunger is depressed.