[jonsee]

What I am looking for is some help in calibrating the four 1966 Mustang instrument cluster gauges, the fuel, oil, temp and amp.

I have yet to take one apart, but from reading a Tech Article out of Mustang & Fords I discovered that these gauges have both a zero and full range span adjustment. Therefore, I want like to calibrate the gauges at the zero and full scale points.

My test equipment consists of a dc power supply with variable voltage and current outputs and a Digital Multi Meter.

I know and understand there will be no voltage reading or current flow when pointer is at the Zero end of the gauge scale, but I don’t know what the reading will be when the pointer is at the 100 % end of the gauge scale. I suspect all (but the amp gauge) have a dropping resistor and if so I can take my measurements either across the resistor (terminals) in volts or current flow through the gauge in amps. So if anyone can tell me what it takes in either volts or amps to drive the indicators full scale would answer my question regarding all but the amp meter.

The amp gauge I know and understand there will be zero current flow when the indicator is reading mid scale, a positive current flow when the indicator is reading in the positive or charging direction and a negative current flow when the indicator is reading in the negative or discharge direction. Again, what I don’t know is what the value in amps is when the indicator is full scale in either the positive or negative direction?

If my theory on any of this is incorrect feel free to correct me.

I would like to thank all, in advance, that is generous enough to take the time to respond to my posting.

Thanks
jonsee

[Veronica]

Hello. What you have is an instrument cluster voltage regulator that works the same way as the alternator regulater. The current causes a thermostatic contact arm to heat up and move off-contact, where it cools and makes contact again.This happens very rapidily, causing the 12V current to average out at about 6V. There should be a green wire with a black stripe comibg from the back of the ignition switch which supplies current to the regulator which is held onto the back of the instrument cluster just to the driver's side of the speedo. Another green wire with a black stripe basically splits into two with one going to the oil pressure and then over to the fuel and the other wire goes over the other way to the water temp. The ammeter gauge is a free-standing circuit with one yellow wire coming from the hot side of the starter solenoid and a red wire coming from the alternator regulator by way of the ignition switch. It's a pretty goofy set-up and it's almost a certainty that your ammeter gauge doesn't work. How people tell if their alternator is working is if the interior lights flicker first slowly with motor at about 1000 rpms and flicker more quickly with the motor at about 2000 rpms.Hope that helps.
And welcome ro AFM.

[jonsee]

Hi Veronica,

Very fast response and you explained the theory very well - I can see where I may need your help again in the future.

However, I should have better explained what I was attempting to do -here goes: My car is in total disassemble and I attempting to calibrate the gauges, on a work bench, with gauges removed from the instrument cluster,and with power supply and digital test meter connected on the two terminals located on the back of the gauge. I will have the front cover plate removed from the gauge to access the two adjustments. One of the adjustments should be the zero and the other the span. And in order to calibrate or adjust the span I will need a known value in either volts or amps. Can you tell me what this value should be when the fuel gauge reads full. This should be the same value for the oil press gauge when the oil press reads max and the temp gauge when the temp gauge reads max temp. The amp gauge is current device requiring me to induce a current signal both positive and negative and read the current in madc or amps dc. Do you know what the required value in milliamps or amps is to drive the gauge needle full scale right or left?

Again thanks in advance for your help.
If my explaination is not clear or incorrect feel free to bring it to my attention.
jonsee

[The Greek]

The instrument panel gauges operate on a pulsing 5 volts from that voltage regulator on the back of the panel . I know that the fuel gauge calibration is determined by a veriable resistor (fuel sender). All of the gauges are the same they are just labeled differently. Except for the amp gauge. The gauges register 70 ohms (as on the fuel gauge) empty and 10 ohms full. So we could say half a tank we would have 30 ohms. All of the rest of the senders are calibrated to work with the same range. Some references say 73 empty or minimum and 10 maximum. I hope this helps.---Chuck
There is one more thing , there is no circuit protection in the amp gauge circuit. If the amp gauge shorts out you will have an electrical fire. It happened to me.

[jonsee]

Thanks Greek,
By knowing the resistance value at zero and full scale and the constant voltage I can calculate the current that I need to calibrate these gauges.

Thanks to both you and Veronica
jonsee

[The Greek]

I want to correct a mistake I made. It would be 40 ohms for half a tank. Sorry but I'm getting a little feeble in my old age.---Chuck