Be sure and put the year in your post headings. It makes a difference.

On most 140s and earlier Volvos the amp light and the turn signal are on
the same fuse and problems with that fuse or its connection are responsible
for some really weird effects. Normally they do include a glowing amp light
though.

If your battery is going down, it might be clear back at the alternator's
isolation diodes. I've had that problem several times over the years but
again, it was usually accompanied by the glowing amp light.

It really sounds like some kind of a ground problem, either a loose ground
or maybe a short to ground in a relay or some such. Might put a meter
in series from the battery circuit with things turned off and pull fuses
till it indicates no continuity. That would tell you (maybe) where the "leak"
is.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma