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Hi all. 1992 EX Sedan w/auto. Had an intermittent starting problem. Voltage read low. Threw a new alternator and new belts on the car. Put it back together, no start. Played around with main relay (checked voltage across connector, was good). Checked voltage at MAP sensor. Good. Decided to hook battery back up and reset the back-up fuse. Car started up and ran. Car only runs at 12v max. Dropped to 11.7 and wouldn’t start again without being jumped. Alternator is properly hooked up. On startup, the ABS and Battery light illuminate until I rev the engine to 2500rpm. They then shut off. I’ll be checking the thermostat ground, but does anyone else have any pointers? Any other possible grounds? I’d like to get this thing rolling.

 

Whats the voltage when the car is running?

 

It only reached 12v while running. I had the battery tested and it was good. My alternator is a Denso replacement and it’s doing the same thing the old alt did so I doubt it’s the alternator itself.

 

Car running the voltage should be at least 13

 

I understand that, that’s why I made this post. I’m looking for possible causes

 

Check voltage from the alternator?

 

Negative test probe on neg battery terminal and positive test probe on the alternator post w/the rubber cap yielded a variation of 16.8 to 18v. This is with the new alternator.

 

K, the wire that connects the alternator to the engine bay fusebox, what voltage is showing there?

 

This one? Looks like it joins a larger harness that runs under the intake to the alt. Measures 12v max with engine running.

 

You're very close to finding the problem. 18 volts on the alternator end but only 12 volts on the fuse box end means that there is a bad connection or a break in the wire. There should be nearly the same voltage on both ends of any wire.

Always disconnect the battery before working on that wire because it is live all the time, and a short to ground will blow the main fuse.