Reverse reading fuel gauge?

[robedney]

Finally got my new fuel tank sending unit and installed. The fuel gauge seems to be reading backward. It would appear that the polarity for the ground has been reversed to negative ground. So, is that the issue? I've not pulled the instrument cluster to look as yet, but is this a simple matter of reversing the leads to the fuel gauge???

[bmcecosse]

In a 67 car it should be a 'hot wire' instrument -when you switch on, the needle should slowly rise to the correct reading. It is not affected by polarity. Or do you have a gauge that flicks to the reading as soon as you switch on?

[robedney]

Pops right up to the level as soon as switched on -- no delay. Is this thing basically a voltmeter?

[bmcecosse]

Well yes - it must be an early gauge not right for a 67 car... and yes a voltmeter, so swap the connections on the rear of the gauge.

[rayofleamington]

AFAIK, the function (full/empty) was reversed around the time the speedo face was changed to the later style (Black face).
so you have two chances - first one being wrong sender and second one is wrong gauge.
Based on your comment about rapid movement of the needle, it does sound like you have an early gauge with a late sender.