Angie’s Blog

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Replacing the dash circuit board – part 2: Trial and Error

I received my circuit board last week and proceeded to reassemble the dash cluster that weekend. If you bagged and labeled everything properly while taking it apart (part 1) then reassembling shouldn’t be a problem. As an after thought, I wish I had taken a picture for reference but it went back together alright nonetheless. Two of my small, copper washers broke into many, many parts while reinstalling them and I had no replacements. I have yet to see the effects it might cause.

So, basically, I’m going to breeze through the re-installment of the circuit board and dash because I ran into no problems, just the reverse of part 1. I’m also breezing through it because, well, it didn’t work. Thats right, all that time and effort and the dash gauges don’t work.

With the dash cluster re-installment, though, you’ll want to find some way to protect your new circuit board from the steering column bolts. Ideally, I would have liked to find some plastic spacers like the kind they use for do-it-yourself car stereo systems but I was in a hurry to get everything back together so I used layers of electrical tape for now. Hopefully those bolts won’t need to be removed anytime soon.

Voltage Regulator

When you reinstall your circuit board and find that everything is still non-responsive, the next thing you want to check is the voltage regulator. The voltage regulator is connected to the circuit board on the back of the dash. If you pulled the circuit board, you couldn’t have missed the little square regulator hanging out back there. In retrospect, when you’re ordering your circuit board, go ahead and order a voltage regulator too. It’s only $40 more and it will save you the heart ache of trying to hunt one down later. Luckily, my friend had one so I only had to wait until he got home that night to pick it up.

When removing and installing a voltage regulator, be careful not to rip the copper sheeting around the regulator’s connectors. These connectors are snaps, such as you’d find on a shirt now days, and can be hard to remove. I took a small specialty flat screwdriver (the kind they repair eyeglasses with) and carefully pried the snaps halves apart. You then snap in the new regulator and screw it back to the circuit board, making sure the screw is snug for a good connection.

After a new voltage regulator was installed, we crossed our fingers and went to install the dash cluster again, seeing if the gauges would register anything. Not a thing.

Sending Units

As mentioned in part 1, if the above parts haven’t fixed your problem by now, testing the sending units can help determine where things are going amiss. There is one sending unit per gauge; an oil sending unit thats located under the hood, a fuel sending unit located at the fuel tank etc. If only one gauge is faulty, hypothetically lets say it was the oil gauge, then you would not bother testing the voltage regulator because the voltage regulator affects the entire gauge cluster. Therefore, if all gauges but the oil gauge were working, then you would 1) check the sending unit and 2) check the circuit board. To check the sending unit you unplug the wire from the sending unit (usually this will be a bootplug or some other little connector) and check for a current with a voltmeter. When we checked ours we got no current whatsoever, indicating that there was no power being sent to the unit. This meant the voltage regulator wasn’t getting any power for whatever reason and it was back to the drawing board for us. Keep in mind that Mustang Monthly goes into this more in depth.

Ignition Switch

As mentioned earlier, all Mustang owners should invest in a Haynes Repair Manual or something similar because this is a situation where you use it. In chapter 10 of the manual it has wiring diagrams for 66-73 Mustang. We traced the connection from the voltage regulator through the circuit board to, where we believed it ended up, at the ignition switch. Now, I already knew my ‘ignition switch’ was going ‘bad’ so I had bought one a long time ago and just never had the opportunity to install it. After almost 40 years, it’s good to change the ignition switch anyways so this provided me a good excuse to slap mine in. When you buy an ignition switch, look for one that comes with a replacement plug. The switches tend to overheat and melt this plug. These switches aren’t easy to find so good luck.

References Pictures:

Steering Column Bolts


Speedometer Cable at Speedometer Head (Dash)
speedometer2thumb.jpg speedometer4thumb.jpg speedometer3thumb.jpg

New Circuit Board Installed

circuitthumb.jpg circuitfullthumb.jpg dashthumb.jpg

Voltage Regulator, 1969 Model


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2 Responses to “Replacing the dash circuit board – part 2: Trial and Error”

  1. jason

    thanks for writing all this down. just happen to be doing the same work on my 69.


  2. Nice article a good repair manual is extremely important. Airtex makes some good quality replacement Ignition Switches.

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