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66 Caprice: my speeometer is not working. I replaced the cable. the instrument circuit panel appears to be in good shape. Is there a specific way it should be connected. and diagrams out to show the appropriate connection?

Same for my fuel gauge. It does not read correctly. It will show empty when I know the tank is full. It will sometime just randomly move.

Any help would be appreciated. Thanks!
 

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Your speedometer is mechanically connected to the transmission using a non-electrical cable. The center of the coaxial type unit has a square drive which turns the speedo and makes the speedometer head turn.
 

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Gas gauge is caused by a bad ground. This problem is so common I think every car overt thirty years old suffers from it.

Speedometer not working is harder to understand as it is mechanical.

Is the speedometer needle moving eradically acting as though it is catching and then speeding up as you drive at a constant speed. Or is it just not telling the correct speed; but moves smoothly up and down the scale?

If the speedo is just off (reporting the wrong speed) then someone has changed the rear differential gearing to a different ratio than what it had in it when it left the factory. You can determine what gear ratio you have now (by removing the inspection cover and counting the teeth on the two gears inside), and then change the speedometer gears in your transmission (there are two a drive and a driven gear). Another less satisfactory option is to buy a correcting transmission (a housing and gears set on shafts inside a box) that bolts onto the outside of your tranny (these correcting geared transmissions are not only expensive, but bulky, and often get in the way of headers).

Big Dave
 

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Two ways to attack the speedometer.

Remove the cable at the transmission and spin it. Get someone to watch to see if the needle moves. If so, the cable and head are ok and the trouble must be in the transmission.

Or

Remove the cable at the speedometer head. Try to turn it. If you can't, that connection is good, you should not be able to turn it at the top end with your hand. Then the trouble must be in the speedometer head or right at the connection at the speedometer head.
 
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