I need help.

So about 9 months ago I replaced my alternator in my 1984 240 turbo. Instead of having my 70 amp bosch rebuilt or replacing it with the same model I went cheap and put in a 55 amp auto parts store brand. After that I had no problems really with the charging system except that my volts gauge flicked when I put on my blinker which I've seen in a lot of older volvos.

Recently things have changed though...and for the worse. Maybe it's nothing but maybe it'll leave me stranded on the freeway. Now when I come to a stop and push in the clutch the volts gauge drops way down with the idle and then jumps back up. Sometimes it slowly goes really low and the battery warning light starts to light up red. To remedy this I can flick my blinker and it kicks the gauge back up to normal levels. Sometimes it stays up and sometimes it kicks back down.

Some things I've tried to fix that I thought it could be were:
1)moisture getting into a cracked rear taillight assembly - sealed
2)loose wires - checked and tightened
3)fuses - checked
4)dirty battery terminals -cleaned

Any suggestions would be most appreciated.

Thanks,
Kris (1984 Volvo 240T wagon, 160,000 miles)