I am currently wiring my MegaSquirt 3 Extra to my wiring harness (MAP based 730 harness) and have only come to one sticking point, wiring up our GM HEI8 ignition module. The instructions given from the MegaSquirt website (http://www.msextra.com/doc/ms3/distributor.html scroll 1/2 way down or http://www.msextra.com/doc/ms2extra/MS2-Extra_HEI.htm) are for the GM HEI7 module and states that the HEI8 is similar.

G terminal = D9 distributor reference input low
B terminal = C7 timing bypass
R terminal = D8 distributorreference input high
E terminal = C8 EST/spark timing output

I have wired everything up and am left with the G terminal on the HEI8 module being blank (because terminal G does not exist on the HEI7). I found that the G pin is "probably" a ground and on my GM Wiring diagrams it is listed as the "Distributor Reference Pulse Input Low." Would it sound correct to have this G terminal grounded at the MegaSquirt ECM?

 

I found the solution and will post it in case anyone has the same question in the future. It isn't a power ground since the module uses the bolt(s) to ground it to the distributor. It is used as a logic ground for signals to and from the ECU, So the wire for G can just be grounded to the MegaSquirt's main DB37 connector at any of the extra grounding locations.