Quote Originally Posted by kbmwgt View Post
Thanks.

The gauge is a 1967 Ford Mustang. The sensor was changed from a button type (sensing 5psi or lower) for the idiot light to the cannister type which Ford had used for years (uses a resistor).

The gauge is a two post type. One for the stepped down power of 5 v and the other going to the sensor. I'm told less resistance in the sesnor more power to the gauge...needle moves.

It seems that power is going through all the right places which points to the sensor/sending unit. I was hoping I guess that some-one would slap me and say you forgot.........something......but. I guess more tesing is needed to track down the problem.
I would think you could check your sending unit pretty easy, but it might take a second pair of hands or some aligator clips on meter leads. Put an ohm meter on your sending unit from the output terminal to the case and you'll see resistance. Then set your air supply regulator to say 40psig, put a nozzle on the hose and blow that pressure into the end of the sending unit. Should see a change in resistance, right? Seems logical to me, but could be too simple?