Locating power drain on 1994 Mazda MX6



I recently had to replace the alternator and battery on my Mazda MX6 (2.5L V6). After doing so, everything seemed fine for the first day. On the second day, I went out in the morning to go to work, and the battery was dead. Jumped it, ran for about 15 minutes & shut down. An hour later, it was dead again. I’m deducing that there is a short/drain somewhere in the system that’s drawing power when the car is off - checked all the obvious stuff (fuses, connections to alternator, no lights left on/doors ajar)…my real question, since it was the last thing worked on before this problem arose is this : is there a component in the alternator itself that can be faulty and allow power to drain from the battery when off, but in all other ways appear to function properly when running? My temporary solution right now is to disconnect the battery at night and at work…other than the pain in the butt of that, everything else appears to be working fine.


Before going further with this, make sure the positive cable is connected and the negative cable is disconnected.
Gently touch a sharp corner or edge of the cable end to the battery negative terminal.

If you have a voltage draw worth worrying about you should see a blue spark. If you see a very faint yellowish spark then that may not be a problem.
If you see a respectable? :slight_smile: spark post back and we’ll go from there.

It is possible an alternator, and even a starter, can have an internal fault and run a battery down quickly.


The alternator could be the cause of the drain. If a blocking diode is shorted it could cause this problem.

By placing a test light probe in series with the battery ground lead you can see where the problem is when the light goes dim or out when you remove the connection to the problem area. If the light doesn’t change when you remove the alternator wires then the trouble is elsewhere. Try pulling fuses one at a time to see if you can find it that way.


Well, tried the cable idea and there is, indeed, a blue spark…it’s nothing huge, but it’s fairly bright and distinct, and I think I understand the difference between the 2 types you describe.

It is probably worth mentioning (and perhaps I should have in the first place) that when the alternator replacement was complete, and I was re-hooking the battery to start it up, connecting the negative terminal produced a significantly larger spark…in fact, it actually temporarily fused the connector to the terminal. I was v-e-r-y wary of starting it after that, but tried anyway, and everything appeared to be fine…until the drain problem surfaced.

My suspicion has been a problem with the ‘new’ alternator all along, but for those who are familiar with where it sits in this model car, it’s none too easy to get at…including even having access to the electrical connections to the unit without pretty much going through the removal process again.

Is there a ‘minimally invasive’ way to further test the alternator while it’s still hooked up?


It does sound like a very healthy spark and this means a serious voltage draw.

As Cougar mentions, connect a test light between the battery neg. terminal and the neg. cable end.
Remove and install fuses one at a time until when or if the light goes out.
If the light remains on after this has been done, then it is probably going to be in the alternator, starter, or possibly a relay that has a stuck set of points.(the most likely relay would be fuel pump or cooling fan relays)

After the fuse business, and before tracing relays, I would disconnect the alternator and then the starter and note if the light goes out then.