Intermittent No Start

Hey all, been having an intermittent no starting issue for awhile now and I am stumped, and would like some input.

I have a 2005 GT wagon that I purchased last May. It was running great for 3-4 months, until I was doing some spirited driving with some buddies. I wasn't beating on it exactly, but she was getting a workout. We cruised back to town and went to go get some food. Waited 15-20 mins to get food, come back, and car doesn't start. Everything lights up, go to turn the key, and can only hear a single click, I'm assuming the solenoid starter? This happened a few more times, after which I did some voltage testing. 12 volts at the battery, 12 volts on the positive wire to the starter, and 12 volts on the starter solenoid wire when cranking.

Thinking it was the starter, I bought a reman. starter off of RockAuto. Put it in, car drove great for about a week - drove it to the store, parked, came back, and no start, just a click. After ~20 mins, it started up again, and gave me a CEL with flashing Cruise light. Ran the codes, and it gave me P0335, P0340, and P0445. Now thinking there might be a ground issue, I took a look at the ones I could find, and the starter ground was not attached - tucked up above the block, most likely from the clutch replacement. Put this back on, car drove great for a week, and same issue again. After the ground was put on, the CEL has not returned. I only got the CEL the one time.

Now sometimes when I try to start the car, the entire electrical system shuts off. I'll have power when the key goes in, go to start, and it all shuts off. What exactly is going on? I've got a few ideas, but electrical issues aren't my forte.

Here's my thoughts: potential bad/missing grounds, bad starter, bad battery/alternator, blown relay or fuse, chewed harness.

Here's all of the grounds I was able to verify are connected - I haven't gone through and cleaned all of them yet, just the easy ones: starter ground, two grounds by driver's side TGVs, both strut towers, torque mount to top of transmission, and the flexible ground straps on the bottom of the heads. Any others that I'm missing?

I'm guessing this car has been having starting issues for awhile. The starter was replaced with a reman. starter at 148k miles (car is sitting at 177k currently). Not sure if related, but the camshaft position sensor was also replaced at 98k miles. The car also had a small accident in the front passenger's side at 150k miles. Maybe something in the harness got cut/pinched?

If anyone has any thoughts/ideas, let me know. My plan is to finish going through grounds and get the battery tested. It is ~3 years old, but when it would crank, it would crank strong.

Quick update: found an old forum post that was exhibiting the same symptoms I was (losing power when attempting to crank when there was previously power), and the remedy was a replacement battery terminal. Since it was cheap and something I was planning on doing anyways, made my way to Advance and spent six bucks on a new brass terminal. Replaced it and car started a couple times, so hopefully it was just that.

I'm going to add in some additional grounds anyways, especially after reading how not great the stock wiring is, along with what 15 years of corrosion and wear will do. Fingers crossed I can finally enjoy some boost weather and get out to enjoy the snow!

Funny, I don't recalling seeing your first post on here on the 19th...

I would have mentioned the ground cable.

I clean my battery post yearly.

You may also want to check the two ground bolts on the bar above cylinder #4 by the brake booster.

I'll assume you know there are two lower grounds from the heads, exhaust manifold to the chassis.

I haven't cleaned those grounds, but verified they're connected at least. I'll run through those when I finish running some new grounds.

One of those lower grounds were missing, but has since been replaced.