David Lewallen

Hi,

Recently put together a DIY MS3X and installed it into my '99 but running into a problem with the charging system.
Stock ECU had no problems with charging system but the ms3 shows battery light on with engine on and Im not seeing 14v at the battery.
Currently battery shows ~12v with engine turned on.

I have added the 5v pull up to the expander board (https://www.miataturbo.net/megasquir...1/#post1576398) and even double checked that solder to make sure its good.
Ive verified that I have a solid connection through the harness from ms3x to the stock wiring harness.
I also checked tunerstudios settings to make sure that the alt control was turned on and set to the same setting as listed here https://www.miataturbo.net/megasquir...1/#post1260846 except warning light is set to Inj E

Any ideas where to start troubleshooting this or has anyone run into the same problem?

David Lewallen

Did some more digging today. Im getting 0.03v from pin 27 on the expander board with the Alt Control's Control Output set to Inverted. If I flip that to normal I see 4.90v. I can see the same voltage on the DP connector at the alternator. Whether set to Inverted or Normal I am not seeing the alternator output voltage and the Alt Control Duty sits at 0%

David Lewallen

I put everything back to stock to check to see if the alternator was toast or not. Battery light is off with engine running and I get 15.2v at the battery.

Im getting 11.XXv on the DP connector with stock ECU in. When using the MS3x I only see 4.9v.

Anyone know what I should be seeing from MS3x on pin X-27/Alt DP when alternator should be charging battery?

David Lewallen

Problem has been solved. All guides, even the thread where alt control for ms3 was introduced, reference using a 1k ohm resistor between VCC and VVT for the 5v pull up. For whatever reason with my setup it wasnt liking the 1k ohm. I dropped down to a 330 ohm resistor and everything is working as expected