Map Light Trigger

[Okie69]

How is the map light circuit supposed to come on? I always thought it was the click when turning the headlight switch all the way counter clockwise but that doesn’t do it.

The only way I can get voltage on the black w/blue stripe wire is to make this tab in red touch the dimmer resistance wire (best name I can think of)

If I turn the knob all the way counter clockwise there’s a small hump on the white knob that hits the contact circled in red but there’s no metal there to complete a circuit.

So what is supposed to hit that small tab to give me 12v on the map light circuit?

 

[DirtDonk]

Is that an original switch? What year?
It’s possible that it was either defective, or broken.
But otherwise yes, that’s how the map light works.

Did you try both directions? I never do remember whether it’s clockwise or counter clockwise, just that it’s the direction that makes the lights in the dash brighter.

 

[Okie69]

It’s a new one from y’all. It seems like there is supposed to be something else there. I can’t be sure because I threw my old one away already like an amateur.

I did try both directions and everything in between.

 

[DirtDonk]

I I can’t be sure because I threw my old one away already like an amateur.

Haha! That’s a really big club you just joined.
Lots of us have been there, done that. But hopefully not any more!
What was the old switch doing that you had to replace it?

 

[.94 OR]

I just redid my map light. I was only pulling about 6V to it so I either had corrosion on the fuse or the connectors at the switch.
Have you checked that you are getting enough voltage to the light to fire it up?

 

[DirtDonk]

Perhaps you can check the output right at the switch.
In Okie‘s case just looking for some power out on the map light/dome light wire.
In your case .94 OR you’re looking to find where the voltage is dropping.
It might actually be right at the switch. Or it could be as you say, somewhere along the line at a connector.

In the meantime, does anyone have a switch (either new or old but preferably old) that they can compare the components to, in the original picture?
Might as well get right to the meat of the question before making anybody twist up like a pretzel under the dash!

 

[Okie69]

More info: it has never had a map light (at least since I’ve had it) the map light wire was capped off when I found it. I’m going to use this circuit to put in some courtesy lights in the footwells and a dome light on the cage.

If someone has a switch that’s loose and can turn it to the position that would turn the map light on and take a picture like I did above I think it would help. Especially if they know that their map light works.

 

[DirtDonk]

I don’t have one here unfortunately (I don’t think) and I’m not in the office so I can’t pull another one off the shelf.
I will see if I can have someone do that though and take a picture, but ultimately it’s better to have someone else here on the forum take a picture of their known good switch rather than pulling one off the shelf that is possibly a another defective one if it turns out yours is.

If it turns out to be a bad switch then of course we will replace it or refund you.
But let’s find out for sure first.

 

[Matt@Wildhorses]

The tab on the left does seem to activate the map light. The ones on the shelf look the same, at least. When the knob is turned all the way to the left, counter clockwise, the ceramic disc has a ledge that lift that contact to energize. Assuming to activate the map light. Tab on the left, runs on the spring on the ceramic disc for dimming. If you have power to the switch, you should be able to check for power on the terminal right above the stubby contact, when the switch is all the way left. There is a click, at all the way left.

Matt

 

[DirtDonk]

Thanks Matt. You lurker you!
Didn’t even have to ask. Glad you’re on the job.

 

[Okie69]

So just the action of lifting the tab is supposed to energize it? I’ll see what that does in a few minutes. I was convinced it needed something with 12v to contact it to pass the 12v.

 

[Matt@Wildhorses]

Thanks Paul! I try to keep my finger on the pulse. Also, yes, from what I can tell, the nub on the ceramic, lifts the contact up at full left, to make contact.

 

[Okie69]

So I went out and hooked it back up. Lifting that tab doesn’t give me voltage on the map light wire that’s on the terminal directly above it. The dimmer on the gauges and all other lighting circuits work perfectly.

 

[.94 OR]

I went and dug out my spare switch. The metal tab you see is the actuator for the dome light switch. It is pushed up by a bump on the ceramic disc when it is turned full left. This connects terminal D1 and D2. From your previous picture, I assume the wire to the dome light comes off D2, so D1 would be the source from the fuse panel.

The dimmer switch operates between the R terminal and the "I" terminal (it wraps over the switch body to the pressure contact). I assume R=resistor and I=instrument?

 

[Okie69]

Awesome! Thank you. So more than likely I’m going to find that I’m not getting voltage to D1. That’s exactly what I needed.

 

[Okie69]

Well guys I just got a lesson in Keep It Simple Stupid. The very first thing I did was check fuses they were all good. A blown fuse is easy to spot, but a corroded fuse that is no longer making contact isn’t as easy. Who can tell where this is going?

I traced the wire that attaches to D1 all the way back to the fuse panel and then started muttering curse words. Checked both sides of the dome light fuse. One side has 12v the other doesn’t. Took the fuse out and rubbed the corrosion off and stuck it back in. Now my map/dome light circuit works!

For anyone stumbling on this thread later what .94 OR said is correct. The little hump on the ceramic disc lifts that tab which connects D1 to D2 internally and allows 12v to pass through.

 

[DirtDonk]

Great news! Glad you found it.
And we all know what a pain it is to do that tracing that you just went through.
Glad you did it though rather than go to the frustration of waiting for a second switch and having it turn out to be “bad“ like the first one!
Good for us too, now we don’t have to send the whole supply back to the vendor and wait six months for new ones!