SI Alternator Charging Lite Blues

[Machiatto]

I have a ’66 Buick that I am wiring up an SI alternator. I have wired this as I have successfully done before and I am getting an issue I have not seen before. I have wired it in similar fashion to this diagram (below) only I used the M & H Electrical Fabricators adaptor kit which basically plugs into the regulator harness and ‘neatly’ jumps the wires correctly. The kit also provide an adaptor which connects to the old style alternator lead and plugs into the SI alternator connector. I am confident that I have it wired correctly.

The issue I have is that terminal 1 (one) from the alternator provides electrical current to the charging lite when the alternator is charging.
Key Off / Engine Off – the charging lite has no power to either side (alt or ign) and lite is off
Key On / Engine Off – the charging lite has ign on one side and grd on the other and the lite is on
Key On / Engine On (assuming the alternator is charging) – the charging lite has ign on one side and charging signal on the other – the lite is off

This is normal operation. The problem that I have is if I have key off / engine off (not running, no charging, the car is just sitting in the garage) then the charge lite is lit. If I disconnect the harness from the alternator, the lite goes out. If I test with the harness disconnected I have battery voltage at terminal #1 at the alternator. This is the terminal that connects directly to one side of the charge bulb. It is my understanding that this terminal should NOT have voltage until the alternator is charging. My parts supplier gave me another alternator and it tests the same.

People have given me all kinds of solutions like I need a diode, or I need a resistor, etc. None of these people can tell me why they think I need these things except to say they have seen it online in some forum. Sending a voltage signal from this terminal on the alternator to the lite is correct so I believe that the wiring is correct – the issue is I don’t think I should have voltage until the alternator is charging. Any insight is appreciated.

https://www.pro-touring.com/attachment.php?attachmentid=118384&stc=1

[TheJDMan]

http://www.madelectrical.com/electrical-tech.shtml

This site can probably answer your question.

[Machiatto]

Actually I spent hours at the madelectrical sight as they are referenced from many forums - especially here. According to everything they have to offer, my car is wired correctly and should not be doing what it's doing.

I would love for someone with an SI alternator to unplug the two wire connector and tell me if they have voltage at terminal 1 (on the actual alternator) when the engine is not running.

Thanks !!!

[TheJDMan]

I just went out with a test light and checked my system. I did the same delete the external regulator and installed a 10SI internal regulated alt. With the key off and engine off I have no voltage on either terminal 1 or 2. When I first installed the SI alternator the engine would not shut off with the key until I installed a diode in the terminal 1 wire. In my case I was getting feed back through that wire which would keep the alternator field winding energized and not allow the ignition circuit to power down.

[Machiatto]

Thanks JDMan !!!

I have the diode installed under the dash on the ignition side of the light which stops alternator power from feeding through to the ignition circuit. Just a different place to put the diode and yes it solved that issue which will happen with internal OR external regulator.

When you checked power, it was with the two wire connector disconnected from the alternator and you checked for voltage at the alternator (not the connector) - correct?

Thanks SO much for taking the time to do this !!!!

[TheJDMan]

No I did not unplug the connector. The way my alternator is clocked I cannot remove the connector without removing the alternator from the mount bracket.

[Machiatto]

That's cool - if it has no power then it has no power - right? If it had power we'd have to disconnect it to see whether the power was from the harness or the alternator itself.

I think I need to source a different alternator. Thanks for your help !!!!!!!!!!!!!!!!!!!!!!!!

[blitzer454]

It seems to me if you have the key off and the lamp is lit then that means that there is a path to ground on the ignition side of the lamp. If the key is in the off position I would expect that one side of the lamp should measure open or very high impedance which prevents the lamp from being lit.

If you remove the connector from the alt with the key in the off position then measure the resistance from the bulb to ground it should be open or high resistance. Or at least I would think it would. Unless for the ignition switch switches in ground when in the off position, but I don't think it does.

It may not be unusual for terminal 1 to have 12V all the time since the battery will back feed through the stator windings and diode trio to this terminal. But I can't say for certainty as I don't have this type of alternator.

[blitzer454]

Now that I think about it more the rectifier should prevent the battery voltage from showing up on terminal 1. But I still don't understand why your bulb would be lit with key off even if you had 12V coming from terminal 1.

[Machiatto]

Quick update - I went to the local AutoZone and we pulled 3 alternators off the shelf and I tested between BAT+ and terminal 1 and all of them read infinite (open) where all of the NAPA alternators read 0 ohms. I installed the AZ alternator and the light functions as it should. Thank You JDMan for checking your alternator.

Blitzer - I still want to answer your question (cuz it's a good one) so I plan to spend some time under the dash with an ohmmeter. I do know that the ignition side of the bulb is connected to several circuits in the dash - like the oil light which uses a grounding switch and therefore provides a ground, albeit thru the oil lite bulb which should lite the oil lite as well (and it does not). But there are several circuits I will chase down. My gut tells me that the Ignition switch is where the ground comes from.