Oil Pressure gage on 76 bronco

[76 MS. bronco]

I have a 76 Bronco with a 302. I am getting a pegged out gage when i turn the key on, just like it's shorted to ground. when i crank the truck it starts slowly going down to 0, it takes about 30 seconds to get all the way down. if i just straight crank the truck the gage jumps to 40 and then slowly drifts to 0. i put the wire straight to ground and it pegs out like the gage is good. i put a new sending unit on it and it acts the same way as the old. ANY SUGGESTIONS??????

 

[Bully Bob]

What 'bout the other gages....are they functioning correctly...?

If not., have a look at the "volt. drop/regulator" attached to the back of inst. cluster.

It should flicker out about 6v.