mgray10

iTrader: (1)

I installed a Commander 950 system in my 88 IROC-Z and now my alternator is not working. The original looked to be on its last leg anyway, so I had no problem going and getting a new one. The new unit was tested in house, in front of my eyes, before I left the store.

The alternator is the standard unit, so far as the 88 IROC-Z 350 is concerned, I do not know for the other years and models. It has the basic +12v battery lead, as well as a 4-prong male output socket on the internal voltage regulator. My car's factory wiring only uses 3 of the 4 pins. The largest pin and wire in the socket goes to the starter solenoid (red).

The next wire is a tan and white wire which used to go to the fuel pump and fan circuit in the fuse bus, however I am not using it so it terminates to nothing, no short to ground and no load present. The ECM provides fuel pump power and the fan relay is supplied directly by the battery; the ECM trigger is ground as factory.

The last wire is a brown wire which goes to the voltage gauge in the stock instrument cluster. It was never touched and the gauge is functioning.

At first I assumed I had a bad ground so I supplied the alternator with a direct and fresh ground to the frame rail and then coupled it to the negative terminal on the battery. I have .1-.2 ohms between alternator case and negative side of battery as well as the frame rail.

I have equal voltages on all of the following: ( +alternator refers to the largest connection on the rear of the case, direct to battery)

- bat. terminal | + alternator
chassis ground | + alternator

- bat. terminal | + bat. terminal
chassis ground | + bat. terminal

alternator case | + alternator
alternator case | +bat. terminal
-------------------------------------------------------------
I have no readings on resistance between: (not 0 ohms, no continuity)

- bat terminal | + bat. terminal
alternator case | + alternator
- bat terminal | +alternator
alternator case | + bat. terminal

This indicates that I have no shorts to ground in my circuit between the bat and alternator.

Now, this is the interesting part: During no engine rpm, idle, and 2000 rpm, all voltage regulator output pins have a very strong resistance to any ground in the system, ranging from 69 (K)ohms to 8 (K) ohms. This is high enough for me to think that, at voltages of 12-15, it is insignificant with regards to my alternator not charging. ...but who knows, not me! This is unchanged whether the regulator plug is attached or unattached.

I not an electrical engineer, yet, but I just didn't do all this in five minutes. Please, no blanket statements like a Haynes manual - check all grounds, check all connections. I have checked and replaced most all of my circuit connections, including the internal connections of the alternator with an entirely new unit. This unit was tested twice, once before leaving the store, and again today after my problem is still eating my lunch. I know the unit is good.

I have also used two different batteries, both of which were working. I even charged both to maximum capacity. There are two possible scenarios which I am assuming are potential problem solvers. I am not knowing, however, therefore I am here. The first is that the fusible link between the voltage regulator and the starter solenoid has failed. The second is that one of the above mentioned wires needs to function as a ground. The wiring schematics for this alternator all show them as being hot, and the regulator having grounds for each, to the case internally. I do have continuity between the alternator and the voltage regulator as it has equal voltage as the battery.




I am stumped.

Mike Gray

Danno

Hook the tan wire to 12 volts thru a 100 ohm 1 watt resistor. That may be the "sense" wire to turn the reg ic on and off. It must be key controlled otherwise the alt will buzz after the car is shut off and it destroy the reg hybrid ic. If the tan wire went to the fuse panel to the "fan/chg" fuse that is in fact the on/off control wire.

mgray10

iTrader: (1)

hey-hey what do ya know? We have ignition! Thanks Danno,

Mike :hail: :hail: :hail: "we are not worthy, we are not worthy!"