Starter won't engage completely had tested it is working properly tried to jump starter relay did not work.....checked wiring harness all good....any ideas please. I Am Stumped

Confused about starter engaging completely .... does the starter whirl without engaging or does it grab for a second and let go without turning the engine? If it's not doing either It may be in the rotary switch that's attached to the tumbler for the key. When you put the key on Acc does everything work? When you turn the key to start does the radio and some accessories cut off?

Is the starter completely mounted to the bell housing? Make sure it is completely seated with no air gap. Sounds like pinion gear is not engaging. Also, if you replaced the pinion, did you get the exact replacement?

The starter was engaging but not spinning. Had it tested it was in fact good. I appreciate ur timely responses and wanted to let u know that what was happening was an original ground wire was broken and not attached to the block when I reattached it the current flowed properly and starter engaged like it was supposed to. It was like magic. I'LL NEVER FORGET THERE ARE THREE GROUNDS EVER AGAIN. Thank you very much.

Glad you got it fixed. I had the same problem on a 65 T-Bird. Cable was attached with only 1 strand of wire out of probably 20-25 strands.

Thank u. I am too. This one was never attached but when I pulled motor out I guess it "reset" everything. Definitely a learning experience for me. Thank you such a quick response tho and I'm sure I'll have more questions.

so im having the same problems where are all of the three ground wires