Dimmer Signal line

I'm trying to understand something here about how the instrument panel illumination works in my 2000 Limited and want to know if I'm on the right track.

Basically, the situation is this: I'm going to be wiring in some extra switches in the near future. They're fairly standard SPST rockers (Carling Conturas, as it happens) with five pins on the rear. Four of them are arranged as two separate switched pairs, presumably for switched positive and switched negative. That part makes sense.

What I'm trying to work out is if the fifth pin (used for illumination) should be tied to the Dimmer Signal line. Basically, I want these switches to dim and brighten with the other instruments, but don't understand how the Dimmer Signal line works - is it basically just a variable-voltage positive off of the instrument dimmer pot? I'm assuming that the switch gets its negative feed from the switched negative pins, so if so it'll work, but I have no idea if it needs to have a resistor in series, etc.

ya ur going the right way. but ground is from main ground not from switch.

jeepdude10000 said:

ya ur going the right way. but ground is from main ground not from switch.

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OK, good to know and thanks. My bad for referring to them as 'switched' positive and negative - what I really meant was that both positive and negative either had continuity or not depending on switch position. I guess that the simple version of the question would've been, "does Dimmer Signal really mean variable positive voltage?"

Do you have a spec sheet for the switches? I'd like to know, mainly, if the illumination in the switch is incandescent (which can be dimmed) or LED (which, generally, can not be dimmed.)

Given the light output of a switch pilot, tho, I'd not worry about dimming it anyhow. And, some switches pull current for the pilot for the circuit under control - which is why you should have a spec sheet to hook it up.

Failing that, give with the specific model number/series of the switches you're using, and someone here should be able to find a datasheet (and if it isn't me, I'd appreciate a copy for the Tech Archives anyhow...)

5-90

5-90 said:

Do you have a spec sheet for the switches? I'd like to know, mainly, if the illumination in the switch is incandescent (which can be dimmed) or LED (which, generally, can not be dimmed.)

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AFAIK, from my brief excursion in disassembling one, they're incandescent. Schematics are at this link (PDF).

Given the light output of a switch pilot, tho, I'd not worry about dimming it anyhow. And, some switches pull current for the pilot for the circuit under control - which is why you should have a spec sheet to hook it up.

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From what I could tell from just pushing 12 raw volts through them, they've at least got the ability to be distractingly bright. As long as they can be tied into the main dimmer circuit, they won't annoy me at night.

Failing that, give with the specific model number/series of the switches you're using, and someone here should be able to find a datasheet (and if it isn't me, I'd appreciate a copy for the Tech Archives anyhow...)

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See above link(s). Between them it should be fairly apparent what's going on - at least, on the switch side. For my part, it's the XJ bits that have me confused.

Me thinks you got it wrong.

The PDF link is very detailed, however it refers to many different types of switches. Generally (there are many different types of switches) an automotive illuminated switch gets its illumination power from the circuit, and uses a ground to complete the light circuit. This means in a true SPST there would be 3 terminals:

Power In
Switched power out
Illumination ground.

The XJ uses a positive variable voltage/current pot to control the dash light intensity. I believe it is a Orange wire...could be wrong. In order to dim your switch lamps, there needs to be a separate power feed for the lamp...if there is you can simply feed the lamp with a tap off the dash light circuit, and you are set.

make sense?


Rev

Rev Den said:

Me thinks you got it wrong.

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Gah!

This means in a true SPST there would be 3 terminals:

Power In
Switched power out
Illumination ground.

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With you so far, but here's my thinking based on the following:

The XJ uses a positive variable voltage/current pot to control the dash light intensity. I believe it is a Orange wire...could be wrong. In order to dim your switch lamps, there needs to be a separate power feed for the lamp...if there is you can simply feed the lamp with a tap off the dash light circuit, and you are set.

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Correct on the orange wire (or, at least, this is what I remember from adding in the Extended Idle switch). However, I suspect that the illumination is getting its ground from switched negative somewhere inside the switch.

Wait... The multimeter says otherwise (i.e., no continuity to any of the other pins from what I believe to be the illumination pin regardless of switch position).

make sense?

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What you're saying makes sense. What I'm seeing at the switch has me more confused than ever, and all three of the switches I've got are doing the same thing.

Hmm..

Are you SURE it is not an LED?

Remember that an LED will only pass current in one direction and that you need a DVMM with a semiconductor setting to feed the LED enough current to turn "on". IF it is a normal bulb...it will be a fairly high resistance, make sure the meter is in the proper range.

Rev

Rev Den said:

Hmm..

Are you SURE it is not an LED?

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Ya know... It's been awhile since I pulled one apart and while I seem to remember it was an incandescent I could easily be misremembering it. I'll put that on tonight's to-do list.

Remember that an LED will only pass current in one direction and that you need a DVMM with a semiconductor setting to feed the LED enough current to turn "on". IF it is a normal bulb...it will be a fairly high resistance, make sure the meter is in the proper range.

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Good points. Checking again later...

hey,

on my 1990 when i tapped into the other dash lights for switches (arb, tranny temp guage) they all dimmed with the dimmer. i just grabbed the light for the t-case shifter for the guage and the cig lighter light for the arb switch. i just got lucky with the dimmer working on them

hth
-Tim