HEI in Mopar ECU casing
Well, after researching the internet literally ALL day, i have figured this out and i should have already known the answer since my boat with 350 GM engine uses this same setup. These 8 pin modules have 10 degrees advance built into them! If you are using this module on a carbureted engine, you have to put the spark timing into bypass mode to set the initial timing so it WONT try to advance the timing, and that requires jumping to pins together and hooking another pin to 12 volts. To verify this, i tried it on my car and sure enough, that stopped the advancing problem! The catch is, you cant leave it plugged up into bypass mode because it is setup to where you have to start the engine, then shut it off, connect the bypass wire, then start it up again to set the timing. once you turn off the ignition, it wont start up again until you have removed the bypass jumper and started the engine without it, then you can hook it up again. You could use it on a switched 12 volts but im not going to bother, i will just get a 4 pin module and be done with it. I happen to have the 4 pin plug that is not used on the 8 pin module when using these with our old cars so i made the ESC bypass with it to verify what i read (and already knew and forgot) and sure enough! Guys running the 8 pin: i bet if you watch it with a timing light, you are getting extra 10 degrees of advance after around 3-3500 rpms. It drops back out at WOT but makes mine ping. Hope this helps!
https://forums.iboats.com/filedata/fetch?id=6932127