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#1 Old Apr 5th, 2005, 02:13 PM
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Dash Light Dimmer Switch

I have a 1990 PF 4x4 fully loaded. I had to repo it from stepson for not making payments over last 2 years. Long story short: I've spent months "undoing" & restoring the damage he reaped upon it with his less that desirable DIY attempts. All is well now except for the dash lights and two gauges.

Problem: No dash "illumination" when running lights are on and neither the fuel or the temp gauges are working. ALL other dash-lights, gages, external lights and internal lights are functioning properly.

I'm pretty sure that the problem is related to a poorly executed attempt at installing a CD player and amp.

Troubleshooting so far:

I pulled the dimmer switch out and tested the 3 leg wire connector with a continuity tester. Results: The brown "ground leg" is good. The other two legs show power (only when the running lights are on). One leg is pink with black stripe the other is pink with blue stripe.

I tested the dimmer switch legs using an Ohm meter. Results: With my ohm meter set to 20K the resistance between the ground leg and each of the other legs was infinite (no reading) at all dial settings. The resistance reading between the two legs that receive power was 1.88 at all dial settings.

I have pulled the instrument cluster, inspected the plastic or tape type PCB and run some continuity tests on it as well. All bulbs are good. If I ground the PCB the bulbs will come on. All appears good except perhaps a diode that could be bad. I tested it with an ohm meter expecting to get no reading but got no resistance.

After sifting through thousands of post I've noticed that the audio and dash circuits tend to be largely integrated and there is where I'll find the problem.

Can anyone help me with the following questions?

1. Should the two pink legs to the dimmer be hot? I assumed that of the 3 legs one would be hot, one would be ground and the third would be the "variable hot output" to the dash lights.

2. Do the results of the ohms test on the dimmer switch fall within normal limits? I thought I would get a reading between the ground leg and either one of the others. I did not expect to get a reading between the two power receiving legs and I thought I'd get a variable resistance when turning the dial.

3. Is the diode on the PCB bad? My (limited) understanding of diode function is to conduct current in one direction after a defined forward bias has been reached. Thus I didn't expected my ohm meter to read zero the instant I connected the probes.

4. Lastly, is it likely that my fuel and temp gages are related to the dash illumination problem? The fuel low warning light works fine. If it wasn't for it I'd have to rely soley on the trip meters to determine when I need fuel.

Any suggestions would be great.

Thanks
Beau

Last edited by jdart11; Apr 5th, 2005 at 02:19 PM. Reason: one pink wire has "blue" stripe
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#2 Old Apr 5th, 2005, 07:13 PM
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the gauge problem could be the voltage regulator (on the back side of the gauges) sorry, I'am in a hurry here, testing the dimmer switch, are you getting more out put when you turn the knob? the switch itself mybe bad..
#3 Old Apr 5th, 2005, 07:58 PM
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Just a thought - is the less than desireable CD player still hooked up? My aftermarket has an auto dimmer swich on it that works off the dash lights - IE lights on = dimmed faceplate. Dimmer swich then controls the brightness.
#4 Old Apr 5th, 2005, 11:30 PM
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Quote:
Originally Posted by 79kz400
Just a thought - is the less than desireable CD player still hooked up? My aftermarket has an auto dimmer swich on it that works off the dash lights - IE lights on = dimmed faceplate. Dimmer swich then controls the brightness.
No that player was removed. I do have another player in it but the problem existed well before I that. I was told that the problems at issue happened after a HEAVY gage hot wire was accidentally shorted during the installation.
#5 Old Apr 5th, 2005, 11:30 PM
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The gauge problem is almost certainly the replaceable voltage regulator. Read this thread for more info: http://wd21forums.damagedreality.com...opic.php?t=336

On the dimmer, it should read varying output resistance depending on the potentiometer's(adjuster wheel's) setting, so that pretty much means your dimmer is shot as far as I can tell. A junkyard replacement might be a good bet. I have a few lying around in my garage if you want to try that route. Let me know.

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#6 Old Apr 5th, 2005, 11:35 PM
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Quote:
Originally Posted by SPEEDO
the gauge problem could be the voltage regulator (on the back side of the gauges) sorry, I'am in a hurry here, testing the dimmer switch, are you getting more out put when you turn the knob? the switch itself mybe bad..
Speedo, I'm not getting any difference when turning the knob. I haven't taken it apart yet to look inside and make repairs. I was expecting to get a variable reading but that doesn't happen.

Also, I haven't yet jumped the ground to the hot wires on the cluster side yet to see what results I get. I'm thinking that the dimmer may need replacing or rebuilt. But somehow I'm not sure that this will be the root of all evil. On the other hand, you never know...
#7 Old Apr 5th, 2005, 11:48 PM
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Quote:
Originally Posted by 88pathoffroad
The gauge problem is almost certainly the replaceable voltage regulator. Read this thread for more info: http://wd21forums.damagedreality.com...opic.php?t=336

On the dimmer, it should read varying output resistance depending on the potentiometer's(adjuster wheel's) setting, so that pretty much means your dimmer is shot as far as I can tell. A junkyard replacement might be a good bet. I have a few lying around in my garage if you want to try that route. Let me know.
88pathoffroad,

thanks for the link I'll check it out. If it's related to the sender in the fuel tank I've done those before and I just can't wait to do it again! However, I did ground the gage and it pegged out so I haven't ruled out the a missing ground connection yet. I'm guessing that the illumination problem is perhaps not connected with the gage problems. If the potentiometer is bad I'll probably try and rebuild it first. If it's toasted I may just take you up on your offer. Besides, you're just up the I-5 road from me.

Thanks
#8 Old Apr 6th, 2005, 12:33 AM
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88pathoffroad & Speedo,

I just took another look at the schematics and found the VR you're speaking of. I thought you were referring to the fuel sending unit. My mistake. I don't remember seeing a VR device attached when I pulled the cluster or I would've tested it. But perhaps I missed it some how.

BTW, if the dimmer switch is bad, what legs on the cluster connector side do I need to jump to test the rest of the circuit?

Thanks for the feedback

Beau
#9 Old Apr 6th, 2005, 11:48 AM
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The pink/black striped wire and the pink/blue striped wire should be the dimmer in and output wires. The black wire is ground. The official name for your dimmer is the "Dimmer Control Rheostat".

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#10 Old Apr 6th, 2005, 03:31 PM
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Quote:
Originally Posted by 88pathoffroad
The pink/black striped wire and the pink/blue striped wire should be the dimmer in and output wires. The black wire is ground. The official name for your dimmer is the "Dimmer Control Rheostat".
Understood. I pulled the rheostat apart and was shocked to find a much more complex circuit design than a typical load bearing potentiometer circuit. It's no wonder that Nissan is very proud of it's parts. It's loaded with typical discreet devices but the main part looks like a typical NPN high power heat sinked transistor but could be a regulator of some sort. Do you know what this device is? The only ID marks I can see did not come up on the site I use to look up semiconductor devices. TD553

I haven't tested the circuit yet and hope to get to that later today. Do you know of a good site to look up semiconductor devices?
#11 Old Apr 6th, 2005, 06:08 PM
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Question

Quote:
Originally Posted by 88pathoffroad
The pink/black striped wire and the pink/blue striped wire should be the dimmer in and output wires. The black wire is ground. The official name for your dimmer is the "Dimmer Control Rheostat".
I forgot to ask... Given the pink/black and pink/blue are the input and output lines, then wouldn't it follow that with the switch disconnected one of them (the output) would be dead? Hot input to rheostat -> rheostat uses potentiometer and circuit to vary the output line -> that supplies the dash illumination voltage. I know this is a basic view and it's probably more complex than the way I'm visualizing it.

As it stands, with the rheostst disconnected both pink wires have power to them. So jumping the pink input to the pink output seems redundant at best.

Another bit of data to consider is when I jump a ground spot of the dash PCB to ground, the dash lights work leading me to believe there is a ground point that is missing or disconnected.
#12 Old Apr 8th, 2005, 01:00 AM
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I bet you $1 he hooked the CD player's remote power wire to the stock dash dimmer wire...that'd explain why you have power on both wires...

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