Instrument Cluster Lights Out

[DanB]

I'm hoping someone can point me in the right direction. The instrument cluster lights don't work on my 71 mustang. I have it out of the car, but how do you test things to figure out what needs to be fixed? With the key and light switch on, there is power to some of the connections coming into the cluster. I have no idea what to look for. I do know that the high beam indicator and left turn blinker lights do work though. There is an aftermarket temp and oil gauge separate of the cluster that work so I expect those on the cluster to be out. There is one bulb missing (see image) but I'm assuming that shouldn't make everything else not work. Any insight would be appreciated.


Update: Thanks for all the comments; they definitely helped. It seems like the main culprits are the little bulb holders. Many of them don’t have continuity through them with the bulbs installed (bulbs tested good). A secondary issue is some of the areas where the holders contact the circuit board are worn down and don’t make good contact. I also checked continuity throughout the circuit board and it seems okay.

There was only one weird anomaly but it might that the identifier of “C-43” that’s right by the CVU (on the diagram) is actually the CVU connections (not 100% sure). I’m just hoping that having continuity from pin 5 to 7 is correct so the fuel gauge works, because there is no continuity from pin 5 to 6. I’ve never looked to see if the fuel gauge registered or not since I’ve been working on this thing. I might just hook the power back up and see.

 

[Steve McMahan]

Here is the 71 wiring diagram from the Wiki page on the site:

https://cdn.imagearchive.com/7173mustangs/images/1971_full.pdf
Starting at the headlight switch, which is what powers the dash lights, trace for the 12 volts up to the instrument cluster connector. Using wire color/marker, you should be able to determine if you’re getting voltage. Lots of us have dash lighting issues, as this stuff is over 50 years old and ignored by the POs. If you have 12 v where you need it, then it’s a matter of checking each of the bulbs and also the blue lense covers which can get so dark, they effectively block the light.

Let us know what you find.

 

[DanB]

Appreciate the help. There is power to the general dash illumination so I'm going to need to look closer at these old bulbs and probably the circuit board in general.

 

[Steve McMahan]

Yea, when I pulled my cluster last year, it had made it 50 years, but it was time for a new ribbon circuit board. I got mine at NPD. If you’re gonna “rebuild” the stock display, you should look into the new LED bulbs, again checkout and likely replace those blue tint lenses for the bulbs, and any other stuff that’s not working on it. Remember, if you replace the turn signal bulbs, you’ll need an LED flasher unit, and the bulb for the Alt idiot light should remain a stock bulb. Good luck and have fun.

 

[Hemikiller]

One of our members (@Don C ?) created a pinout diagram for the printed circuit.

While you have the cluster out, open the gauges up and clean them out. Repaint the inside with gloss white paint, and replace any melted blue diffusers. It'll make a huge difference in the illumination level.

 

[72MustangSprint]

Try changing the bulbs first , might be simple fix

 

[vintageman]

Also, you may want to reach out to Randy (aka: Midlife), he is a well known and supporting member here and he created a hardwire kit for me on my 73 instrument cluster that does not use the ribbon circuit board. Works very well and no issues since installation. Good luck.

Tom