OBD II engine light trigger?

[mkassab]

I need help to determine what triggers the OBD II engine light to turn on.... a +12v or a (-) ground negative to the engine light..... I'm NOT referring to a code causing the trigger...

Here's my full right up and pic in my build link: https://thefactoryfiveforum.com/showthread.php?44055-Mark-s-35-Truck-Build-Extended-w-Gen-3-Coyote&p=575026&viewfull=1#post575026

thx Mark

[edwardb]

The Ford Performance MIL has +12V at all times and is illuminated by the PCM closing the ground. So that should be compatible with your Dakota setup. The one issue you might find though is there is apparently some leakage on the ground circuit, because even when officially “off” the MIL glows slightly. On both my Gen2 and Gen3. Others have reported it as well. I’ve played around with resisters and different LED’s but wasn’t able to improve. Barely visible in daylight but more visible at night. Maybe more savvy electrical experts can fix, but I haven’t been able to. I consider the slight glow as “PCM is alive” indicator. 😉

[mkassab]

Thanks Paul. I expected as much. As I do see a low glow in the eng warning light. I'll try to tap into the bulb ground to my Dakota Digital (DD) cluster. If the eng light in the cluster comes on from the ground leakage as you spelled out, maybe I'll try a ground to the DD cluster via a simple relay, i.e., I'd have the ground from the PCM trigger a relay hoping the "leakage" ground isn't enough to trigger the relay without a real code? Fingers crossed.

Mark