Hey guys. So my issue isnt specifically with the starter, in fact the starter itself works fine. A little back story:

Last week I finished swaping my 3.8L engine in my 2002 regal. Replaced with a 3.8L out of a 2005 grand prix. No supercharger on it. For the last week everything has been aces, with the exception of one time during a start nothing happened when i turned the key. Gave a single knock as if the starter was cooked. I popped the hood, checked all my harness'* and connections including the battery connections, turned the key and started up right away. Aside from the one issue the car has been a dream . . . until today that is. Drove the car all morning, stopped for lunch, jumped in to start it up and nothing. The starter knocked like the last time, but no turn over from the engine. Tried all the usual stuff, got under it, gave it a bang with the hammer, nothing. A single knock from the starter and no turn over. Went and grabbed a new starter, installed it, and nothing. Just the same knock from the new starter and that'* all. Except for the fact that one of the harness'* running low voltage wires was getting so hot it began to smoke, melted the plastic off of one of the five wires, but no turn from the engine. I'm not sure what that harness is for but it runs across the front of the intake. Had my car guy swing by, tested the old starter and it was fine. My car guy says it seems like the starter isn't getting power. It seems like a wiring issue but I'm not really sure where to start with this. Finally got my car back and it only lasted a week. Has anyone run into any similar issues? Any suggestions would be greatly appreciated! I really wanna get my baby back on the road. Thanks folks.

Inspect the starter wires from the battery down to the starter. Including the engine ground at the block.

Alright, ill start there. As I said i found wiring that was already mangled, getting really hot. Ill look for any issue from battery all the way to the ground. Have you ever heard of an issue similar to this? If so, suggestions on how to fix it? Is it as simple as replacing whatever wires are shot? Or is it more likely to be a relay issue? I just want to have a second plan if there is nothing visibly obvious with the wiring. Thanks again!

Usually if a wire is getting hot under a high amperage load, that means the wire isn't carrying the load very well. Imaging trying to put a house fire out with a garden hose hooked to a fire truck. You're trying to shove several hundred gallons of water per second through a 1/2" hose.

In electrical speak, corrosion at one end or the other or even a semi break in the middle can cause issues like this.

Got it. So if I were to find an issue with the wiring at some point in the line my best option would be to replace that wiring harness with something new? Now that I think about it, a break or corrosion makes sense. It was an issue that came up suddenly, could mean that the problem was there and over time got worse to the point where it finally broke somewhere yesterday. Thanks a lot! This place is great. I love my regal, just want her running and running well. Trying to take care of her as best I can and learn as I go.

Further information about this.

Checked all the wiring from battery to the starter. Found nothing However it was suggested to me that the alternator could be the issue. That if the voltage regulator can fail and cause this problem. Unfortunatly my mutlimeter crapped before I could get a reading from the voltage line out of the alternator. Wondering if this is likely to be the issue. Id like to go grab a new alternator in case this is the issue so I can save time fixing her tmr. Is it possible this could be the issue? Is it worth grabbing a new alternator before I get a meter on the old one?

Check starter enable relay circuit?

Have you confirmed the engine will turn over by hand?