engine and drivetrain Electrical light going on and off when car is hot

[josh72ooh2]

I've got a head scratcher...

 

I have one of the alternators sold on Ebay that is a 85AMP upgrade with an internal regulator.

I am still running the stock voltage regulator because if I disconnect it, the dash light goes on. 

 

I have an EFI set up on my car that is controlled by a custom chipped 1996 318 ECU.

http://www.bmw2002faq.com/topic/170941-fuel-injection-photos-with-94-bmw-318-chipped-ecu/

 

Lately, when the engine is hot and I've been driving it for 30 minutes or more, the dashboard voltage light goes on at idle.

I step on the gas, it usually goes away.  It isn't consistently going on at every traffic light, but it will pop on and go away within a few yards, or a few blocks of driving the car.

I have a voltmeter gauge in the car and the voltage dips to 12v or under at that time too.

 

I swapped out the stock regulator and put in an adjustable modern voltage regulator similar to this (but a different brand):

http://www.euromotoelectrics.com/product-p/vr-extadj.htm 

The dash light still goes on but the old regulator had an occasional glow/flicker to it.  Now the light is either on or off with the new regulator

 

My 2 year old son is obsessed with playing in my car so occasionally a light got turned on and the battery went low.  I had the battery tested, and it is fine. It is charged and been no issues for 2 weeks. 

 

I took the alternator out and brought it to the shop in Van Nuys that sells them on ebay.  They tested it and it is fine. 

 

The ground wire is thick and connected well.

 

My thought is that when the alternator gets warm, it stops performing properly.  i don't want to buy a new one unless I know that is the issue.

 

Any other ideas?

 

Thanks in advance.

 

-josh

[SydneyTii]

Mmmm I think there is a wiring mod, have a search

[SydneyTii]

Actually you need to disconnect the external regulator and follow the instructions on Holts site

http://www.zeebuck.com/bimmers/tech/318alternator/318ialternator.html#tii

[josh72ooh2]

I did the mod that bypasses the regulator... i think.  I'll double check later but I remember only using the one wire from the triple connector to the stock alternator. But it still required the use of my stock regulator.  

None of this wasn't an issue until recently.

I did the mod that bypasses the regulator... i think.  I'll double check later but I remember only using the one wire from the triple connector to the stock alternator. But it still required the use of my stock regulator.  

None of this wasn't an issue until recently.

[josh72ooh2]

I have it hooked up as per the instructions on the link, and here:

http://www.bmw2002faq.com/_/technical-articles/electrical-and-ignition/how-to-swap-a-320i-e21-alternator-onto-a-non-r60

 

But again, when the car is warm/hot, is when I have issues. Is there a way to test the alternator's performance while on the car, running, and when that light pops on? 

Like perhaps measuring amps or volts across the B or D terminals?