I have a 94 Honda civic ex 5 speed with a y8 swap z6 head and z6 wiring harness. I replaced the alt. about a week ago and charged the battery cause the old alt. drained it. It ran fine for a good 5-6 days. Now the battery light came back on. The battery is good just not holding its charge. If I leave it off for 5+ hours the battery will die and wont start. When driving it, it runs fine and wont shut off. I know its not the alt. and battery. What else could it be?

 

First thing I check is the alternator belt for tightness.
If there are shiny places on the edges, it may be slipping.

 

A temporary solution until you get it fixed is to put in a battery cutoff switch
at the negative ground terminal. That is also useful for when you are working
on the car and the first instruction is: "Disconnect the battery ground". lol

Cut it off when you park the car. If the battery still loses charge, you have a
battery problem. A New battery is no guarantee that it is a good new battery.

The testers at the a-parts store will detect a surface charge that tells them
the battery is good.....but if it drains when disconnected, take it back.
Request another battery with authority.
Most places will swap out a bad battery once.

 

Let us know what you find.-Bob

 

The battery stays charged when I disconnect it. I'm gonna take the belt off and put it back on now. And make sure its tight. I will let you know. When driving it doesn't shut off or anything. It stays running but the battery light stays on unless I idle or go over 2000 Rpms. Never had this problem.. weird..

 

Some cars will light the batt light under acceleration.
With a lot of accessories cut on, the light comes on sooner under acceleration.
...and sometimes the idling alternator cannot handle a lot of accessories.

 

I did a charging system test and it said that the voltage regulator failed. Is it internal or external on the alt.

 

By '94 probably it was internal.