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No instrument panel lights


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Took the Monte out last night and noticed none of my instrument panel lights were working. Headlight switch seems to be working (headlights work, dome light turns on when switch is turned all the way to the right).

 

The printed circuit board and light bulbs are only 2 years old. They worked in the fall without issue. Any ideas what it might be?

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Something common to all the lights. I would start by looking at either the headlight switch or the connector. I cannot remember if the printed circuit shares a ground point, that could also be worth looking into. I think the common for the lights goes through the connector that plugs into the printed circuit.

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Fuse? Mine was rusty and needed to be cleaned.

Bruce

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Check the headlight switch ground. There is a metal ring that is mounted between the switch and the panel with a ground wire connected. I'd check that and any other grounds under there. I believe there is also one that goes to the emergency brake assembly that is for the dash lights too.

 

Steve

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The dimmed circuit. Fed from a jumper in the headlight switch to the rheostat in front of the switch. Then it goes to the fuse box, through the short fuse on the bottom, then out through a gray wire to the cluster plug and the lights in the heater-A/C control panel and radio.

 

If all these lights are out, check the fuse.

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On my 71, the fuse for the dash lights is very small, 4 AMP I believe.

post-76-0-82111500-1525481668_thumb.jpg

 

To test the fuse, pull the light switch out, turning on the lights, then test for power on both sides of the 4 AMP fuse with a test light.

You need power on each side to rule the fuse out as a problem.

Ground wire from the headlight switch, was also mentioned.

post-76-0-88591700-1525481864_thumb.jpg

 

What has changed since they did work? In my case I ask what did I try to fix or change!

 

 

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As this fuse gets it's power AFTER the rheostat, your voltage reading may be screwy.

 

The best way to check this fuse is to pull it and check for continuity with a self-powered tester or an ohm meter.

post-201-0-96007400-1525484989_thumb.jpg

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All you have to read is voltage on both sides of the fuse. You can also check continuity with the fuse installed, it will still read open if the fuse is blown.

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If there's any problem with the power coming from the rheostat, you won't see any voltage on either side of this fuse. If you check for voltage at the fuse but the problem is elsewhere, the fuse will "read" bad-when it's not.

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I think we are talking the same thing. If you don't have voltage at the fuse the issue isn't likely the fuse. I have never had an issue reading an installed glass fuse in the past, either with a volt meter, an ohm meter, a continuity tester,or even my fancy multimeter. LOL

 

I hate pulling a good fuse to check it. Even with a glass fuse puller you risk breaking it, or at least I do.

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Yes, we're talking about the same fuse. Neither end of it is connected to 12 volt power. If the feed to it from the dimmer rheostat at the light switch is bad, you will get no reading at the fuse, regardless of which side of the fuse you probe.

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....aaaand this is why I don't post more.

 

Of course you are right Paul. What was I thinking, advising him to check for voltage? (a test light would work as well, forgot to mention it earlier)

 

Keep us posted as to what fixes the light issue Mike. I wont reply any longer, but I'll be happy to hear when you get it fixed.

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I hope ya come back with the fix as mine lights have also done the same thing recently.  his thread came at a good time.  Later RJD

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Troubleshooting the instrument panel & cluster lights:

1: Turn on the headlights to confirm the headlight switch is receiving power.

2: With headlights on, look for any working cluster lights AND lights in AC/heater panel AND radio, if original is in place.

3: If none of the above lights work, turn off headlights and remove at least one lamp from the cluster. Bench test with a 9~12 volt battery. If it doesn’t work, replace with new and start over, checking this one lamp. If it now works, replace the rest of the lamps. If it did work, reinstall and continue to step 4.

4: Remove the short fuse at the bottom of the fuse box. Test the fuse, out of the fuse box with a continuity tester, self powered test light or ohm meter.

5: If the fuse is bad (open), replace and run through the test again from step 1.

6: If the fuse is good OR replacing it with a new one does not fix the lights, replace the headlight switch/rheostat.

 

Voltage path: + power to headlight switch. From headlight switch through jumper terminal to rheostat mounted on switch. From rheostat to fuse box to small fuse. From small fuse to various panel lamps in gray wire. NOTE: The fuse is NOT connected to any other power source in the fuse box therefore when the headights are off OR the rheostat is in it's lowest setting, the fuse will  show zero volts even if the fuse is good. NOTE: The ring ground at the headlight switch is for the rheostat. The lamps throughout the dash receive their grounds from other ground points.

post-201-0-28696600-1525658681_thumb.jpg

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https://www.youtube.com/watch?v=uQ_wsaQWwzE

 

Made a vid of how to test that fuse.

 

I have never created a youtube video before so be nice.

 

A few notes:

 

My tester is circa early 1990's and the ohm tester is on the fritz.

I should have prefaced this with a statement about the first step in troubleshooting a circuit that doesn't function at all is a fuse check. 26 years as an AT taught me that. So what I have presented in the video is the first step in determining what the problem may be by either eliminating the fuse as the culprit or identifying the fuse as the issue.

The video only addresses fuse checking, it doesn't address any other portion of the system troubleshooting. However if no voltage is present the issue is likely in the switch or the wiring. I know 40+ year old wiring can be problematic however 9 times out of 10 the switch will be the problem.

I wanted to remove the fuse to demonstrate what the test would be if the fuse was bad, however my fuse block is relatively brand new and I don't have a spare glass fuse handy, so instead of risking damage to my current fuse I briefly described the test results if the fuse was blown/removed towards the very end of the video.

 

I am relatively confident that between my quick video and the in depth circuit description provided by Paul anyone should be able to attack a no instrument light problem with confidence.

 

Enjoy!

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