l have a 1978 chevy 3x3 and l have put a new starter in. l have no power to the cab at all. No lights no guages no brake lights no head lights.. l do have 12.45 volts in the battery.. it will turn over if l jump the starter..

Sounds like you left something disconnected when you put the starter in. Double check.

OR, you fried a fusible link somewhere.

It is been awhile for that old of a truck. l am thinking it has a 350 engine it should have three wires one large and one small that will fit the large stud on the starter one small one that goes on the small stud this engages the starter when you turn the key. the small wire on the large stud feeds the power to the cab.

first it the solenoid on your starter if is not check on the frame under the hood and replace it if it is on your starter take your starter back off and go get the solenoid tested that is probably your problem