first test tosee if the sending unit is working with the method I described in grounding the sending unit wire for a second with the key on- the gauge should peg. The sendimg unit is cheap enough though that you wont be breaking the bank by replacing it. They should already come with pipe compound or teflon paste on them. If not, use a small amount on the threads to not throw off the reading- you need to have the sending unit/fitting make decent contact with the manifold.