Out of all the things I've struggled with on my car, this is the first thing I wasn't able to find the answer for...anywhere. As such, I am posting the solution in the hopes it helps someone else and to start finally giving back to this forum.

So, like the title states, I was experiencing the battery light coming on in the dash when I was at high rpm/load. I didn't realize until later that this only occurred at WOT; high rpm/load by itself did not trigger it (but that was the impression I was under until I solved it). I did not notice any loss of power, just a rapid blinking/constant battery light.

After looking over my logs, I finally noticed that the Target Voltage was normally running at 14 but getting lowered to 12.5 and that coincided with when my dash lit up. Turns out, under Alternator Control, there is a setting for WOT target voltage and it was set to 12.5 volts instead of the standard 'run mode target voltage' of 14.0 from the base MSPNP map. Also, the WOT TPS percentage was set to 101% (theoretically impossible), which made that section actually grayed-out/uneditable, which to me indicated it was NOT ACTIVE. Well...that's where I was wrong. It was definitely active and definitely the cause of my problems. I went back and looked at my logs and the 12.5 target voltage occurred exactly when I was at 101% throttle. I recently adjusted my throttle cable so that explains why I haven't been experiencing this issue since I installed the MS.

I temporarily enabled this section in Alternator Control by setting my WOT TPS % to 99, set the WOT target voltage to 14, and disabled it again with a 105% WOT TPS percentage just to be safe. Drove it hard for an hour afterwards and didn't see the light come on once. Before I came to this solution, I was led astray by thinking my alternator was dying, the belts were loose/slipping, loose ground connections, and a faulty IAT sensor. Pretty much tried addressing all of those things before I studied the logs more and realized the problem.

 

Thanks for this writeup, it solved my battery light at WOT!

 

Awesome!! Seriously just knowing it helped even one person makes it worth the effort to type it up

 

Thanks this also helped me stop spending money on charging system parts. Although now that I understand whats going on I will just leave it that way.

 

KB10ae - let me add my thanks as well! Exact same problem, read your post (tried not to get too excited), opened Tuner Studio, and yep - WOT was set for 101%! As soon as I changed WOT to 99%, all the other options below it became available. Problem now solved, very happy Below are my "before" and "after" settings. Thanks again.

 

Yea I thought about leaving it that way but really can't imagine any discernible difference with keeping it on. On a pure track car I would probably leave it on but no way am I staring at that light coming on (or removing the bulb) for street use.

 

Absolutely and thanks for sharing your experience. I'm learning Megasquirt has an annoying habit of having inactive/grayed out settings actually have an effect. My A/C would cut out at 60 MPH and above and I couldn't figure out why since the setting for that wasn't enabled! Then once I enabled it, changed the MPH threshold to 90, and turned it back off, my A/C now works above 60 mph