Topic: Checking Gages For A 66 Mustang -

[jwc66k]

A friend was tossing a 66 instrument cluster that he had "smoked" and I said let me check out the gauges and strip the hardware first.
Here's what I found:
Gas, temperature and oil pressure gauges resistance: 16 to 20 ohms; with 4 volts DC applied to the terminals on the back, positive to the RH terminal when viewed from the front, the gauge will slowly (5-10 seconds) rise to about 3/4 full scale deflection. Applying 1.2 VDC the same way will give about 1/4 deflection. (I grabbed three "used" D batteries which is the reason for the low input voltages.)
The ammeter works differently and couldn't test it (it was "stuck"), but I think this one was the cause of the "smoke".
I assume that the 65 gas gauge (65 GT is the same as 66 above) and any other gauges used in newer years (67-73) will give the same readings or results.
Jim     

[midlife]

Yes, you're on the right track.  I use a D cell or a 9V battery, applying voltage to the positive side of each gauge.  If it deflects, it is good.  The same goes for the ammeter.  Just be brief on attaching the voltage so you don't damage the gauges.  The power to the gauges is to the right of the driver when installed in the dash. 

[GT500KR]

Yes, you're on the right track.  I use a D cell or a 9V battery, applying voltage to the positive side of each gauge.  If it deflects, it is good.  The same goes for the ammeter.  Just be brief on attaching the voltage so you don't damage the gauges.  The power to the gauges is to the right of the driver when installed in the dash.

Is there a way to tell if a temp or fuel gauge is reading within factory spec? In other words, a certain voltage would make it read in the middle?

[jwc66k]

Is there a way to tell if a temp or fuel gauge is reading within factory spec? In other words, a certain voltage would make it read in the middle?

A full needle deflection should be seen when 5 VDC is applied across both terminals (bench test). That 5 VDC is the voltage from the constant voltage regulator mounted to the back side of the instrument cluster. A middle deflection should be obtained with 2.5 VDC if the gauge reads linear (it should). There are mechanical adjustment on the back side of the gauges, but I haven't had the opportunity to see what happens when they are moved. I think they adjust the needle at each end, high and low readings.
Jim

[67gta289]

How about checking a tach - what is a safe method?

[midlife]

A full needle deflection should be seen when 5 VDC is applied across both terminals (bench test). That 5 VDC is the voltage from the constant voltage regulator mounted to the back side of the instrument cluster. A middle deflection should be obtained with 2.5 VDC if the gauge reads linear (it should). There are mechanical adjustment on the back side of the gauges, but I haven't had the opportunity to see what happens when they are moved. I think they adjust the needle at each end, high and low readings.
Jim

I don't like applying only voltage across a gauge.  A better method for fuel is to ensure you have a quarter tank and take a reading on the gauge.  The gauge deflection can be adjusted by turning the (usually potted) trim potentiometer on the back of the CVR one way or another.  If it is too far off, the float arm angle can be adjusted by trial and error.

There are ways of calibrating tachometers, but not with equipment normally found in hobbyist's hands.  Even I do not have the appropriate tools for that.

[jwc66k]

I don't like applying only voltage across a gauge. 

I do. That's the way I was taught.

A better method for fuel is to ensure you have a quarter tank and take a reading on the gauge. 

I did the testing on my kitchen table (workbench has an engine on it) with an ohmmeter and 3 D cells in a series battery holder.

The gauge deflection can be adjusted by turning the (usually potted) trim potentiometer on the back of the CVR one way or another. 

There are no adjustments on a Ford a constant voltage regulator.

There are ways of calibrating tachometers, but not with equipment normally found in hobbyist's hands.  Even I do not have the appropriate tools for that.

No tachometers were injured in this presentation. In fact, there were no tachs involved in my effort, however, you are correct about equipment not normally found in hobbyist's hands. I do have a couple of dual trace oscilloscopes and signal generators on the bench, normally.
One of the gauges I tested had a bent needle and may have other problems. In my normal idle curiosity, I'm going to take it apart, with pictures. 
Jim

[midlife]

There are adjustments on a Ford CVR.  On the back side, you'll see a small post, typically potted in epoxy.  If you remove the epoxy, the post can be rotated.  That post controls the resting position of the bimetallic strip.  When that strip jumps between the two positions, the time spent on each position determines the overall voltage.  By adjusting one of the positions, you can change the output voltage enough to change the needle deflection about a half-gauge worth.  Trust me: I've done this several times.