Dash lights don't work - HELP!

[Tonka Man]

One of my rescue cars has an issue with the dash lights.  I checked the little 4A fuse and it is good.  Even checked the continuity of the fuse because it is so tiny.

Any ideas of why my dash lights do not work?  Something else I can check?

[Rob Peters]

I am guessing either a bad ground or the circuit board is bad.

rob

[stangeba]

Is there power on both sides of that tiny fuse?

Headlight switch has a dimmer (looks like a coil spring) that sometimes can break.

Ground wires for the dash lights and headlight switch need to be connected.

Here is a link to some pictures of my 71 showing the ground wires and H/L switch.

https://1971montecarlo.wordpress.com/2023/09/21/71-monte-carlo-clock-pictures/

 

 

[Michael Boyte]

I'm with you on that one Rob , quite so often it's nothing more than a bad ground.  

[Scott S.]

I replaced my light switch this summer because the running and dash lights wouldn't work....

Is it just the dash ? Or have you checked the other lights ?

If so, I'm in agreement with Rob on this one. 

[Tonka Man]

I have a digital multimeter.  What do I set the dial to so that I can check either side of the fuse?

[Tonka Man]

My dimmer switch on the floor is difficult to change between bright and dim.  I sticks and then eventually clicks over.  If I replace that, could it help the dash lights?

Where are there other grounds I can look?  I looked at your pictures Bruce but I wasn't tracking for where the dash ground might be.  What did I miss?

[cbolt]

On 11/10/2024 at 3:00 PM, Scott S. said:

have a digital multimeter.  What do I set the dial to so that I can check either side of the fuse?

your multimeter should have a 20 and a 200 vdc setting. The 20 should work just fine. Ground the black lead and touch the red lead to either side of the tiny fuse to check voltage on both sides. You stated you checked the continuity across the fuse and its good, so the only thing you will be able to see is if voltage is getting to the fuse. 

A test light works well in that situation as well. 

Side note. Its early and I really messed up the quote text process. Need. More. Coffee

[cbolt]

I know this may seem obvious, but did you check the bulbs? The phrase "rescue car" makes it sound like a barn find type situation and it could be as simple as the bulbs are burned out. 

You also say you changed your headlight switch this summer because the dash lights didn't work. Did the H/L switch replacement fix that problem at the time? Did you clean and inspect the H/L switch electrical connector? Could be corroded and the friction of changing the switch was just enough to make a good, but still corroded, contact between the switch and the connector. 

Voltage tracing isn't too difficult but can be time consuming and frustrating. 

[DragCat]

When checking fuses in the fuse panel, I prefer a test light. That way you only have to handle the probe  but make sure you have a GOOD ground. 

If you pull the fuse you set the meter to ohms, good fuse = 0 

[DragCat]

35 minutes ago, cbolt said:

Side note. Its early and I really messed up the quote text process. Need. More. Coffee

Ive already been schooled by Dennis, don't post until after your first cup 🤣

[stangeba]

The headlight switch needs to be pulled out at least to the first click, for power to be sent to the tiny fuse for testing.

I remember reading about someone who replaced the headlight switch where the original one had 7 connectors but the replacement had only 6. How many did your old switch have vs the current switch? This may only be for 71 and 72 Monte Carlos, pictures from my 71. Notice the "connector" that connects the two top right terminals? I have read that this could be missing on replacement switches, causing problems

 

[stangeba]

Ground wire (bottom right) on my 71 and I think there is a second one but can't find a picture of it yet.......... I know one attaches to the parking brake assembly.

[stangeba]

Here is my parking brake assembly showing the attachment screw location on my 71.

[Tonka Man]

Wow!  You all are the bomb!  When it comes to electrical issues, I'm purposefully ignorant.  If I can't change a fuse or bulb, I'm in over my head.  Guess I'm going to have to learn.

I'll work through all of these suggestions.  Fortunately, even though this is a rescue car (I call it a tree find instead of a barn find), it is fairly unmolested.  One or more of these suggestions should get me on the right track.

[Paul Bell]

The path of power for the instrument cluster, AC/Heater panel, radio and center console lamps is as follows:

When pulled out to either on position, the headlight switch feeds power to it’s internal rotary rheostat. This power goes to the fuse block in a dark green wire. This wire feeds the short fuse. The short fuse feeds a gray wire that goes to all the lamps in the circuit.

As the voltage in this circuit is varied by the rheostat, it’s best to test with a test light while the headlight switch is pulled out and being rotated while testing. If all is well, the test lamp brightness should vary while turning the headlight switch knob.

The feed to the rheostat in the headlight switch may come off the tail light fuse in the fuse box.

There are several ground points in the system, all need to be good.

The headlight high/low beam foot switch has nothing to do with any other lighting.

[Scott S.]

Actually Paul, I think the feed to the rheostat comes off the same point as the ctsy battery connection. Then comes back to the various fuse connections. 

That's how I'm interpreting the diagram.... 

Scott.

[Paul Bell]

Hey Scott,

I have a note that says they come from the headlight feed in the switch and another note that says it comes from the tail light fuse on an orange wire.

The reason for the latter is that if you blew the tail light fuse the cluster would go out prompting the car to be checked out.

I have a switch somewhere, I'll test it when I find it.

[Scott S.]

I'm curious as to that orange wire...... 

When I parked Montelishi for the winter, I noticed that the right rear tail light wasn't working on the top half, but the signal and interior lights were all good. 

Might be tied to the signal/hazard lights ??

[stangeba]

Or the taillight half of that 1157 bulb is just burnt out?

I remember purchasing new 1157 bulbs for my 71 25+ years ago, and they were junk. The metal base was WAY smaller than the original ones so the bulb was not in the socket tightly enough and failed to work most of the time because of this poor / loose connection. 

[Scott S.]

I haven't pulled it apart yet.... Waiting until spring now. 

I've have those issues with "off shore" bulbs to.

Stick to the ones made here now-a-days.

[B-Man]

Id like to resurrect this thread since I'm going down a very similar path as @Tonka Man.

Here's the deal:

- pull the headlight switch on (either position) and no dash lights. But ALL of the headlights, tail lights and side markers come on

- with the headlight switch pulled out, put a test light and volt meter to either side of the short INST LPS  fuse, no light and no voltage.

- checked continuity across the fuse, I get the beep

- the right side of the TAIL LPS fuse holder is gone (see photo: no idea, a PO thing) but there is still 12V to the left side of the holder and the tail lights DO work (hmmm a bypass?)

- with the headlight switch pulled out I turn the rotary dimmer and the headlights, even high beams, flicker all over (new LED headlights bulbs)

- with the headlight switch in OR pulled out, using alligator clips I pull 12v off the remaining left side of the TAIL LPS fuse holder and pole the INST LPS fuse and I DO GET dash lights (a few bad / old bulbs for sure). They are dimmable using the rotary knob. There is a small spark when I poke the fuse,almost as if it's already seeing 12v but it may be nothing.

@Paul Bell states above "When pulled out to either on position, the headlight switch feeds power to it’s internal rotary rheostat. This power goes to the fuse block in a dark green wire. This wire feeds the short fuse. The short fuse feeds a gray wire that goes to all the lamps in the circuit."

So any thoughts on where th fault might be? Worst case I run 12V to the INST LPS fuse via a relay and key-switched power. But if it's a simple, known fault I'd like to fix it.

Note that I will eventually be pulling the dash out but I am really trying to finish projects and be ready for the summer rather than doffing the hole any deeper

Thanks for any and all help

[Scott S.]

Personally, I'd start with the headlight switch. Mine did something similar about 2 years ago.... First the interior, then the running lights. 

New switch cured that.

But by the looks of things, a new fuse box (and maybe wiring harness) aren't to far down the road.

seeing as you're thinking about pulling the dash, It'd be a good time to do it. 

[kpcsgasp]

On 11/9/2024 at 3:00 PM, stangeba said:

Is there power on both sides of that tiny fuse?

Headlight switch has a dimmer (looks like a coil spring) that sometimes can break.

Ground wires for the dash lights and headlight switch need to be connected.

Here is a link to some pictures of my 71 showing the ground wires and H/L switch.

https://1971montecarlo.wordpress.com/2023/09/21/71-monte-carlo-clock-pictures/

 

 

If you choose to replace the switch BEWARE! Some non-OEM switches are missing a terminal. Makes troubleshooting fun!

[B-Man]

@Scott S., any thoughts on a good source for a replacement Fuse Box and Headlight Switch?

I know there are a few parts resellers on here. So I suppose I could post a "Want to Buy" ad