Electrical: 2R map light switch

[52-fan]

Before I install any components back into my truck I am cleaning and testing them. I am working on the map light circuit right now. I know that the switch on the dash is just another path to ground just like the door switches. There is only one terminal (red arrow) so I thought the switch grounded through the housing to the dash. The problem is, I can only get continuity by touching the little nub (yellow arrow) on the back. Is the switch defective or am I overlooking something?

[jackb]

I'm right on this install with you at this time and can't wait for the answer.....

[TWChamp]

I'm also interested in the answer, although this switch is a bit different than my 1950 Land Cruiser. My switch was so brittle that it crumbled like a sugar cube when I touched it.
I bought another switch from French Lake, and installed it, but so far it isn't working. I haven't looked into the problem yet, but all 4 door switches work fine.

[Mort]

In your picts you do not have a complete circuit. The bulb is an unusual one where the ends of the filament are directly connected to positive at one end and negative at the other with two solder contacts on the bottom. The bulb's brass base (and bulb holder) is not part of the circuit. therefor without a bulb you have a break in the circuit.

[Mort]

to test the switch attach one end of your meter to the switch housing and the other directly to terminal (red in your pict). I think you may be using the wire lead with the bulb holder in it, and that will throw you off without a bulb.

[52-fan]

I made up a new harness and used a 1004 bulb like my Dodge truck uses in its dome light. If I ground either door wire the light works. If I attach a ground wire to the switch body the light will not work. If I clip the ground to the button where the yellow arrow is, the switch works as it should.
I guess my next step is to open up the switch and see what's in there.

[TWChamp]

I wouldn't open the switch. Can you just solder a ground wire to the terminal by the yellow arrow?
Or you can use a thin brass strip to connect that terminal to the underside of the mounting tab.

[52-fan]

I wouldn't open the switch. Can you just solder a ground wire to the terminal by the yellow arrow?
Or you can use a thin brass strip to connect that terminal to the underside of the mounting tab.

I have been pondering that too. The little terminal moves in and out some as the switch is moved. That might complicate the attachment.
I also didn't know what the heat might do to the internal parts. I do have a soldering pencil that can apply the heat in a specific area. I may try that. If I ruin this switch, I'll just have to get another one, but I like tinkering and hate to discard usable parts.

[52-fan]

I went down to the basement and gave it a shot. The 25 watt soldering pencil was too small so I had to use a 140 watt soldering gun. The actual work was a bit tricky, but I mocked up my system and everything seems to work. The copper wire has enough flex to let the switch move.

[Mort]

If the switch does not work with positive to the red terminal, and neg to the switch housing, then the switch is not making contact internally. Because you say it will work if you attach a ground to the yellow contact, we can assume the internal slider is moving. Then the problem is most likely dirt/corrosion.When you move the handle back and forth, both terminals should move a little bit. If not it's a broken or stuck spring. I would open the switch. With a little care it's not that big of a deal. You will note that there is a little U shaped part around the terminal (yellow in picts above) that contacts the bottom of the housing. This and the housing must be clean. Of course clean all the little brass parts while you have the switch opened. I use steel wool, just be sure to clean that out too. Putting it all back together is not hard. Whole project takes 15-20 min. You will have an unaltered switch that should last for many more years

[Mort]

By the way, if you order one of those 6v bulb kits advertized on E-bay (ads with big red letters) you will not get a 88 bulb unless you specifically ask for one.

[jackb]

I can't remember if this truck is 6V or 12 V, neg or pos ....? I'm thinking Mort is giving 12V , neg ground info. I only ask because I am into this same issue with my truck soon. Mine is 12V / neg.

[Skip Lackie]

I can't remember if this truck is 6V or 12 V, neg or pos ....? I'm thinking Mort is giving 12V , neg ground info. I only ask because I am into this same issue with my truck soon. Mine is 12V / neg.

Switches don't care about polarity, and a switch designed for 6 volts can easily handle 12 volts. This same switch was used on all C-cab trucks, 1949-64.

[52-fan]

Mine is 12 volt, but all this switch does is provide a path to ground anyway. In reality the door switches will be the ones getting a workout. I imagine it will be rare to use the switch.

[PSB]

I have the same issue on our 49 truck with no overhead light... Still have not figured it out.. now 12v neg ground.. I am thinking of changing hot to the switch and see what happens..