This morning I started the Jeepster and the ammeter was at 0 and the voltage was only 12 volts.  When I just turned the ignition on the AMP light does not light. Looks like we have a charging problem.  Since I see people all the time who have no clue how to do this I will try to explain the process.

Step one is the wiring diagram.  On a GM 10si if you are not charging and the amp light is out either the amp light circuit or the alternator is bad.  If the amp light circuit is broken the alternator does not regulate properly so I will try that first.  I have customized my alternator install but the amp light wiring is the same.  The yellow highlighted gray wire runs from the regulator of the alternator through a connector on the firewall to the instrument panel connector (pin H) to the light.   Battery voltage is supplied to to the panel, goes through the light bulb, and to the alternator.  The regulator in the alternator shunts that to ground when the alternator is not producing, thus lighting the light.  So lets check that.

First just to be sure I am checking the battery terminal on the alternator.  The meter is set to volts and the negative lead is grounded.  I have 12 volts here so no problem.

Next I turned the ignition key on and checked the gray wire at the alternator.  There should be voltage here but there is not.  This points to the wiring rather than the alternator.

I removed the connector and checked again.  That is odd.  I am getting some voltage but I would expect more.

This is not likely to be the problem but it is easy to check.   I pulled the amp bulb out and checked it using the resistance setting on the meter.  Bulb is fine.

The problem is likely to be at a connector.  So I disconnected the battery and popped the instrument panel out.  With the meter still on ohms I put one probe in the alternator connector and one in cavity H on the connector.

144 ohms is not great but I just have the probe stuck in the hole.  This should work.

I also checked the instrument panel and it is good.  But the pins on the connector were pretty dirty.  This could just be a loose connection.  I put Deoxit on the pins and plugged the panel back in.

If any of this helped shorting the gray wire to ground should turn the light on.

Bingo!  Probably a loose or dirty connection.

I put the alternator connector back on and started the car.  Now we are charging just fine.    I wonder if it will stay fixed?

While I am out melting in the heat I will go ahead and replace the positive battery cable.   The old one is thin and frayed.

Here is the new one I picked up.  It is #2 gauge and 30″ long.  My negative cable is #4 so I could have used that but they did not have one 30″ at the auto parts store.  This will be fine.

The other end of the cable is on the starter so I took that big nut off and disconnected it.

The only thing holding the old cable now is this clamp.  The screw goes through the wheel well and is all crappy so I sprayed it with penetrating oil and wire-brushed the end sticking out into the fender well.  Eventually I got it to turn without stripping the head or breaking the screw.

Put the new cable in and all is well.  The terminal connector uses a metric nut and it is much fatter than the negative cable but it is far better than what I had before.

Here is what I bought in case it helps.