I decided to take a risk, and rather than try to diagnose all the grounds, I'd fix something I knew was marginal, and see if it helped. And it did!
The whole electrical system in this car is iffy, largely because someone who owned the car before me went a little wirecutter-happy and had totally wacky priorities. Like, for example, the fact that there's fairly new wire run to the trunk for... a subwoofer? That, and the audio head unit wiring is all chopped--more evidence for a subwoofer plan. Bad enough, but this person felt that audio wiring was more important than fixing this:
Yeah, that'll drive a subwoofer. Not.
See that electrical tape around that black wire running across and down from the negative battery terminal? That's the wire in the "pull codes" sticky that attaches to a screw right next to the battery, which also branches off to provide... the main computer ground. And now, my computer is freaking out, almost as if its power connections were a bit iffy. Hmmm....
So, before chasing down gremlins, I figured now was a good time to fix what clearly needed to be fixed, at least on the negative side. If that fixes the problem, hooray! If not, well, I needed to do it anyway, and I've at least eliminated a possible source of trouble.
I'd even bought a set of replacement battery cables a while back, but just hadn't gotten around to swapping them out. So I was ready to go.
Swap done, dome light still worked, fired it up, and boom. Started right up, ran as well as it ever has. No super-rough idle, no check engine light, nothing, just sweet, sweet rumble and the whiff of leaky exhaust. The voltmeter on the dash was higher than usual, too.
The positive cable is still the nasty one. It's late, and I'm cold, so that will wait for another day. But not the "car dies on the road again and gives me a scare" version of "another day".
)
