I'm having weird problems in my 88 rx7.
A few days ago I noticed the lights in the instrument panel at night were unusually dim.
Yesterday I went out to start the car and the car labored to start as if the battery was bad and after the car started the battery gauge was showing 9 volts.
I replaced the alternator about a month ago, so I thought it would be the battery and got a new battery on warranty after the old battery tested as bad at the auto parts store.
After replacing the battery, upon startup the battery gauge reads almost dead on at 12v with no accessories on and when I need to drive home from work at night and use the headlights it drops slightly under 12v.
Previously before the dim instrument panel lights, it would stay at about 13-14v while in operation, but now it's at a hair over 12 at speed.
Today I checked all the fuses to rule that out and there was no bad fuses and no change in the gauge readings.
After replacing the battery, the car no longer labors to start and has no noticable problems running as of yet.
At this point I'm not sure what to check next.
I have no multimeter so direct check like that are out for me for now.
Could it be the voltage gauge itself giving a bad reading?
-T

 

W/o a multimeter it's basically a guessing game. When you do have a multimeter you would place the red lead on the B+ terminal which is a single black wire bolted to the alternator and then place the black lead of the meter on the battery negative terminal as the ground source and w/ the meter set to DC voltage and the car running, no accesories turned on, the reading should fall within 14.2 to 14.7 volts. If it doesn't then you have a problematic alternator and if it falls within spec then the gauge is likely faulty.

 

I just went and grabbed a multimeter today and performed the test as described above.
at idle, the voltmeter read 11.87 volts, so I'm assuming this means my month old alternator is bad?

 

get another alternator.
The Remanufactured Stuff from places Like AutoZone are crap.
Change it out and charge your battery,go for a 2 mile drive and double check.
Yeehah.,.Just hit over 8000 posts!

 

I guess so, luckily it should still be under warranty.