help!!!Electrical problems again

[180sx]

well few weeks ago alternator dies so i got a used one put it in drove for few days, after work on the 3rd day after replacement car won't start got a boost drove it home fine at home i took a shower and was about to head out car wouldn't start again gave it a boost took a voltmeter outpoot 12V so took the battery our refilled the holes with distilled water charged it for 12 hours drove fine for 2-3 days and yesterday on the way to work my radion kept going off and on than my rpm started dropping and it stolls. hooked up another car to it to charge my battery abit to get home checked other car puts out 14V to my battery started my car checked only 7 volts drove it to battary place they checked battery holds charge alternator only poots out 7V. is it my bad luck with used altewrnator or what ?? what else can be cousing this on 89 s13 with about 200K

[yellow_jacket]

If you bought a used one that is probably the problem. Check all the connections though.