Hello everybody, I'm a pretty smart guy when it comes to electronics,
which can make me very dangerous. I have a problem with my 1989 Chevy
S-10 Blazer that I need some help with. Here's the deal...
About 4 or 5 months ago, I started to notice that the battery wasn't
holding a charge, and decided I needed to replace it. I was lazy, and
didn't do so. Since this was our second car, we only drove it once a
week or so, and when we did, we usually had to jump-start it. That
worked fine. Last week, I finally decided it was time to replace the
battery. I went and bought a new batter, pulled the old one out, and
put the new battery in. I connected the new battery and expected to
see the under-hood light to turn on... it didn't. That was weird.
Well, let's see if it will start. Nothing. Not even a click.
After some diagnosis, I have found a few weird things. First, when I
connect the battery properly, I get a perfect 12.56VDC when measuring
at the positive (+) battery terminal and the engine block. This tells
me that the block is properly gounded. Good. Then I tested at the
"terminal block" and the engine block. Nothing. So instead of using
the engine block as a ground, I actually put the probe on the negitive
post of the battery. Nothing. Okay, so it looks like I'm not getting
any positive flow to the "terminal block" located in the back of the
engine compartment. I've tried to trace it back, but I haven't done a
very good job. Okay, so something is obviously not working right, but
what is it?
Okay, so here is where it gets strange (or at least I think it is
strange). I decided to disconnect the negative (-) connection to the
battery. Essentially, I have the positive side hooked up, and the
negative is just hanging there. With this done, I would expect to not
be able to get a voltage reading off of anything except for the two
battery posts (since the car is no longer grounded). This was not the
case. I put the negative probe from my multi-meter on the negative (-)
post on the battery and touched the case of the alternator. My
multi-meter (DMM) jumped up to 12.56VDC. What? Okay, let's try again.
Put the ground probe into the negative post of the battery (but note
again that the car frame itself is not grounded) and touched the engine
block. DMM reads 12.56VDC. Okay, so now it looks as though my car has
changed into a positive ground.
I can tell you where I think the positive flow is coming from... I
just don't know if this is to be expected. I believe that the cable
running from the positive (+) post on the battery to the post on the
alternator is causing the housing of the alternator to be positively
I don't really know what is going on, and like I said, I know just
enough to cause some problems. Any help or insight into this issue
would be GREATLY appreciated. I am looking to sell this car, and I
really need to get it running.
Oh, and one last thing... I quickly mentioned it above, but when the
battery is properly installed, absolutely NOTHING works in the car
(from an electrical standpoint). Not even the dome light.
Thanks in advance for any help.