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72 Monte Carlo instrument cluster gauges conversion


72 Monte Carlo

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I installed Sonnie24's tach/gauges conversion kit, and it has the lower right bulb for the tach that will not light up. The new circuit board has it coming from the #7 pink wire location at the dash plug and goes to the left side stud behind the speedo, than it goes down to the tach lower right side bulb location. It branches off that stud and goes to the lower right bulb of the speedo and then heads over to the right side stud of the horizontal block behind the fuel gauge, and then it heads up underneath the vertical block that gets installed behind the temp gauge. According to my manual that pink wire actually used to be for the seat belt buzzer and the seat belt warning light. I don't see a seat belt warning light on the instrument cluster bezel though.

The bulbs are all new LED bulbs and all the other bulbs light up just fine. I tried swapping the bulb holder and bulb with another one, and it does the same exact thing. I would think that when you pull the headlight switch to the marker light position, that the pink wire circuit path should have power to lite up the positive side of the bulb behind the lower right side of the tach.  

Here is a simple picture I drew up. The Red circuit path is coming from #7 pink wire (not lit up when lights pulled to marker light location) location of the dash plug and the first bulb is the one that's not working. The Blue circuit path comes from #6 and heads to that problematic first bulb that's not working. My test light shows no power coming from #7 but it has power coming from #2 Gray and a couple more have power.

The bulbs are circled in Orange.

Here's how I have the dash plug re-wired per Sonnie's instructions;

1. Double Light Blue - not moved from original spot

2. Grey - not moved from original spot

3. Black/White

4. Black

5. Light Green

6. Blue

7. Pink

8. Tan - not moved from original spot

9. Brown

10. Dark Green

11. Tan

12. Double Dark Blue - not moved from original spot

 

Anyone have any ideas?

 

72 Monte Carlo instrument cluster wiring #7 run.jpg

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I replaced the dash bulbs with led’s off ebay.  I ran into two issues, the first was the trace of the printed circuit lifted off the mylar(I guess the substrate is mylar) I simply put it back where it came from and carefully reinstalled the bulb holder over the trace, the second issue I ran into was the led’s I purchased where polarity sensitive(not all are), you may want to turn the bulb around in the holder and try again.

J

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Doug, I know the '72 wiring and conversion kit are different from the '70 so I do not pretend to know exactly what you are dealing with. 

Just some general troubleshooting ideas:  Since that bulb is the only one that's not working, it is probably not a ground issue.   You have already confirmed that both the socket and the LED bulb work when plugged into other locations with power so it has to be a power supply issue at that bulb's proper location.  If power is available at the contact surface in the circuit board surrounding the bulb socket, it has to be a conductivity issue between that and the bulb socket contacts. As Dan suggested, bending the socket contacts to insure a firm contact when seated is also something I had to do for some locations. 

However, I suspect it may be a continuity issue where power is not getting to the contact surface surrounding that bulb socket.  I would trace the circuit path back from the socket to the power source (dash plug) and test for continuity between those points. If there is no continuity, you probably have a break in the copper foil circuit path on your circuit board (have seen it before).  If you have continuity there, then I would check for continuity between the ends of the wire supplying power to the dash plug at the proper location (wire color is not important - continuity is).  Note even if you have wire continuity, there may not be conductivity (proper contact) between the dash plug and the circuit board at that specific wire location when the plug is installed.

So, I would check for voltage at the proper location in the dash plug when the dash light switch and ignition switch are both "on" .   If power is coming to the dash plug at the proper location (not sure if it is #6 or #7) and there is continuity in your circuit board to the bulb location and the bulb socket is properly seated (with a known good bulb) and the bulb still doesn't light, it almost has to be a conductivity issue in your dash plug.  

Since you unplugged, moved and re-plugged some wires in the 12-pin  instrument panel connector plug, I suspect that specific power wire's contact may not be fully seated in the plug - just a guess.   If I remember right, each wire going into that plug is terminated with a springy copper finger which makes contact with the circuit board when installed so I would be sure those fingers are not bent and the contact surfaces are all clean and bright. Good luck.

 

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5 hours ago, MCfan said:

Doug, I know the '72 wiring and conversion kit are different from the '70 so I do not pretend to know exactly what you are dealing with. 

Just some general troubleshooting ideas:  Since that bulb is the only one that's not working, it is probably not a ground issue.   You have already confirmed that both the socket and the LED bulb work when plugged into other locations with power so it has to be a power supply issue at that bulb's proper location.  If power is available at the contact surface in the circuit board surrounding the bulb socket, it has to be a conductivity issue between that and the bulb socket contacts. As Dan suggested, bending the socket contacts to insure a firm contact when seated is also something I had to do for some locations. - I've already bent the contacts on the bulb holder and they are touching the circuit path. 

However, I suspect it may be a continuity issue where power is not getting to the contact surface surrounding that bulb socket.  I would trace the circuit path back from the socket to the power source (dash plug) and test for continuity between those points. If there is no continuity, you probably have a break in the copper foil circuit path on your circuit board (have seen it before).  If you have continuity there, then I would check for continuity between the ends of the wire supplying power to the dash plug at the proper location (wire color is not important - continuity is).  Note even if you have wire continuity, there may not be conductivity (proper contact) between the dash plug and the circuit board at that specific wire location when the plug is installed. - I will test the path from the socket to the #7 pink wire dash plug circuit path and verify if the path has continuity or not. I will test the connector of the #7 dash plug connector and see if it transfers to the bulb socket circuit path as well.

So, I would check for voltage at the proper location in the dash plug when the dash light switch and ignition switch are both "on" .   If power is coming to the dash plug at the proper location (not sure if it is #6 or #7) and there is continuity in your circuit board to the bulb location and the bulb socket is properly seated (with a known good bulb) and the bulb still doesn't light, it almost has to be a conductivity issue in your dash plug. 

Since you unplugged, moved and re-plugged some wires in the 12-pin  instrument panel connector plug, I suspect that specific power wire's contact may not be fully seated in the plug - just a guess.   If I remember right, each wire going into that plug is terminated with a springy copper finger which makes contact with the circuit board when installed so I would be sure those fingers are not bent and the contact surfaces are all clean and bright. Good luck. - Question, since the #7 pink wire was originally for the seat belt buzzer and seat belt warning light, then having it try to light up any bulbs in the instrument cluster does not make sense. The dash plug connectors are all seated and locked into place at the same depth. 

 

 

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Okay, more troubleshooting and mystery bulb solved. After looking at the bulb in question, finding out there is continuity on both sides of the bulb socket to both the #6 & #7 dash plug pins, that Instrument cluster  bulb sits behind for the oil light to light up in case the engine gets low on oil. 
 

I have an aftermarket oil gauge in the car, so I don’t need that bulb to light up at all. I ran a continuity test between the old oil sensor wire in the engine bay to the back of the instrument cluster bulb, and yep it flows all the way through just fine.

With the lights on the market light position, that oil light window is just barely lit up because of the other bulbs being on in the gauge cluster. 
 

What’s the best way to eliminate that oil pressure light from getting any residual light from the other gauge cluster bulbs so it doesn’t illuminate?

Thanks for all your help!

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Well since all of know just how much of a PITA it is to get the instrument cluster out of our Monte's, I'm thinking of taking a model car paint brush with some flat black paint to just cover the backside of the oil light lense, as I fear that electrical tape might fall off some time down the road.

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Doug, glad you diagnosed the "problem" - sorry I didn't think of that earlier. 

I'm sure you have your reasons for not wanting that red oil pressure light to come on but its primary/sole reason for being there is to visibly alert the driver if the engine loses oil pressure while it is running which is something a pressure gauge won't do unless you are watching it closely.  I have a working accurate oil pressure gauge in my '70, as well, but I don't have a habit of watching it closely most of the time.  I personally like the "belt and suspenders" approach of being alerted by the light of low oil pressure and then confirming it by the analog gauge so I left my dash light operational.

I know the red oil pressure light also comes on whenever the ignition key is turned to accessory and the engine is not running but sometimes that alerts me that I left the key in and the ignition "on".   Personal preference I guess ...

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I would leave it alone, but it seems as though there should have been some kind of separation wall or tube internally behind the tach gauge to keep the tach gauge bulbs from illuminating the oil light when the instrument cluster lights are on. 

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Update - I removed the new circuit board from the left half of the dash and gently laid it over to the passenger side and then removed the two bottom screws that hold the tach gauge into the gauge housing. There was a cardboard tube that's painted white on the inside that is supposed to isolate the oil light from getting any ambient light from the tach gauge lights. That tube was not in the correct position, so I relocated it to it's proper position and re-installed everything, and now the gauges are lit up without the oil light getting any ambient light from the other bulbs in the cluster. 

I re-installed the dash by myself again, and checked all the lights again, and it's good to go, and now on to the next small mechanical task to get done, and then it's finish a little bit of body work and spray some etching primer on the bare metal body.

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Getting closer to being done with the small mechanical stuff. I only have a few things left to do;

1. heater control panel LED bulb, and LED glove box bulb

2. install a new throttle cable.

3. install new bushings in the rear control arms.

4. Paint the dash with SEM interior Black paint - it's currently factory green, but I'm going with Black Interior

Then it's finish the body work on both front fenders, and passenger door, and then it's ready for etching primer on the bare metal body. 

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  • 4 weeks later...

I have a brand new BA9S LED green bulb for the 1445 heater control panel bulb, but it will not light up the LED bulb at all, no matter which way the bulb is in the socket. But when I put the regular halogen 1445 bulb in the socket, it lights up. I'm not sure why it won't light up the LED bulb.

I'm assuming it's because there's not enough draw on that bulb socket, and it won't light up the LED. I'm thinking of converting it from the 1445 bulb socket to a 194 bulb socket.

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  • 8 months later...

hello, i am upgrading my dash to the gauge set up from sonnies and I have the cluster removed. I was wondering if there is a way to test the dash lights after upgrading to led before i put the gauge cluster back in the dash? Any info is appreciated.  Thanks

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3 hours ago, Regmon said:

Have you or anyone done this on the beach using a different power source other than the wiring harness from the  the car?..

Working on your car on the beach. You are dedicated. Hope you have a cold one with. JK. HAHA 😆. I know what you meant but I just had to. 😂😂

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