The idiot light for the alternator is pretty simple
and doesn’t generally trip any codes in
the OBD2 computer.
May have been a bad battery, a poor cable connection
or possibly the first signs of a charging
system issue. Keep Driving!

I've always been a Haynes fan, but IMHO
Volvo has the better wiring diagrams...

Just came across this: https://www.amazon.com/Nokian-Hakkapeliitta-Studded-205-55R16XL/dp/B07QYZM5C4/ref=sr_1_17?crid=1DY6FN7VXZ8SV&keywords=hakkapeliitta+8&qid=1570649879&sprefix=hakkapeliit%2Caps%2C241&sr=8-17 Outrageously Good Price! They’ll turn your P80 into an Angry Little Badg...

That's not an antenna or any part of the fob receiver. It's just a status LED for the alarm and a solar sensor for the ECC. You should already have central locks and maybe even the dash mounted lock unlock switch. IIRC, you need to add the 5-pin fob receiver module that mounts above the passenger-si...

As pointed out above, those all share an automatically resetting, thermally tripped circuit breaker. ( Volvo calls it an Automatic Fuse. You'll need to remove the four torx screws on the top of the fuse box cover near the windshield to remove it and access the circuit breakers and relays in that par...

IDK about 850’s, but there’s a mounting hole under
the Volvo badge on ‘98-‘00 70 series cars. Volvo
started shipping with a side repeater in those
fenders for ‘99-‘00. Available in JYs everywhere!

Each door lock motor has a small protection device. As designed, if the motor should draw too much current and begin to overheat ( for instance, because of a stuck switch ), the device opens the circuit to the motor to keep it from melting down or damaging switch or relays contacts in the system. As...

Here's the other page that goes with the wiring diagram above.
It looks like the hot lead is pin 1 on the visor. I hope this helps!

Maybe this will help?

Good News - Your car doesn't have any relays or shunts between the PNP switch and the reverse lamps. The 2000 70 series cars were pretty simple and don't have any goofy stuff like a Central Electric Module. You turn the key, the relay that provides power to accessories ( 2/6 ) energizes and makes po...