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Discussion Starter #1
I recently changed the circuit board on my instrument cluster. Fuel gauge was working fine before I changed the board, temp gauge never worked and I have an aftermarket temp gauge under the dash.
Ammeter, oil pressure, and speedometer are all working nicely, but the fuel and the temp gauges are both pegged to the right. While the stock temp gauge was indicating overheating, my aftermarket temp gauge was reading 190.
I'm mostly concerned with the fuel gauge.
Could this be an issue with that little voltage regulator on the back of the cluster?
 

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The factory oil pressure gauge works off of that IVR also. If it is working as it should then apparently the IVR is also working.
The gauges pegged to the right indicate a direct short to ground.
 

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Discussion Starter #4
Maybe it's the plug not quite lining up with the terminals on the board?... Some of the lights work, some don't. The indicators aren't working either. Before I replaced the board I had one indicator, now I have none, and most of the dash lights didn't work. That's why I replaced the board.
Hoping this is something I can fix without taking the dash apart... again...
 

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I doubt it's the instrument but more likely the temp sending unit's impedance not matching the stock gauge esp if aftermarket. I know the fuel gauge reading is always mucked up with aftermarket sending units and it can be calibrated.

Are you running a Motocraft temp sending unit in your manifold? I had an aftermarket one some silver thing and it was always reading hot but the motor wasn't. Put in a Motocraft new temp unit in the stock location behind the T-stat housing and the level dropped by 1/4 of the mark. Now that spring is heating things up and I have a new manifold, new self-tune and timing bumped to 12 deg I'm seeing it etch up high when sitting. I let it for about 45 sitting min in Drive with E-brake stopping the car to get a good heat soak test at 75 deg today. Got near top of the range but engine was holding fine even without the shroud and I've got an aftermarket alum rad that is a good one. My engine might be .40 or .50 over (it's 302) I have no clue. I have a 180 deg stat.

I'm going to break down and get the IR heat gun. Side benefits....you can test people for Coronavirus to see if they're running a fever :p But I think my engine is just fine. They always soar when stilled for a long time and grinding in traffic and then fall to 1/2 or less when moving in open areas.
 

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It's mostly foggy in my mind but I'm pretty sure I remember reading bad reports about the '69 aftermarket circuit panels. As I recall somebody was making a wiring harness for the '69 models to replace that circuit panel. Isn't there a website devoted to the 69 Mustangs? FourEyeMustangs.com or some such name. I'm sure you could learn more there.
 

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Discussion Starter #7
I doubt it's the instrument but more likely the temp sending unit's impedance not matching the stock gauge esp if aftermarket. I know the fuel gauge reading is always mucked up with aftermarket sending units and it can be calibrated.
I have 2 temp gauges: the stock one on my instrument cluster and my aftermarket which is under my dash. The aftermarket one is working fine. I installed the aftermarket one back in 2005 shortly after purchasing the car. I swapped the 302 out for a rebuilt 351W... which immediately began overheating. Shortly thereafter it was revealed to me that I had a 2 row rad and needed a 3 row. New at the game back then.

It's mostly foggy in my mind but I'm pretty sure I remember reading bad reports about the '69 aftermarket circuit panels. As I recall somebody was making a wiring harness for the '69 models to replace that circuit panel. Isn't there a website devoted to the 69 Mustangs? FourEyeMustangs.com or some such name. I'm sure you could learn more there.
This is the only forum I'm on. I laid the new circuit board over the old one... things looked like they lined up nicely.
What I couldn't see was how the plug lined up with the board when plugging it in. Not much "give" on the harness even with the dash out, so I couldn't position it so I could see anything. I just plugged it in and hoped for the best... Oh well... Nothing's ever easy with these old beasts, is it?
 

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Yes circuit replacements are known to have issues. It was Midlife who did the 69/70 gauge conversion to a wiring harness with bulbs to replace circuit flexicrap. I’m not sure if he is still doing it, but I remember you had to be committed to it, because it as something that could not be undone. I think you had to cut connector off your wiring harness as it “plugged into circuit panel”. I think you had to add in a Chevy connector or something like that ...


 

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He used to be a regular here but vacated during a mass uprising when VMF shifted ownership a few times ago. He’s on that other site now. Stangfix.com
 

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Discussion Starter #10
Thanks Coupster. I do have that flexible thing with the rectangular plug. First time I took it apart (never having done one before) I thought the design was... well... less than genius, especially if the plug didn't quite line up with the contacts.
 
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