Join Date: Mar 2002
Location: Austin, TX, USA
I can imagine how the module affects the signal. That would be an interesting investigation - how are the modules different and which one is better.
But it comes down to this. The circuit in the tach isn't high tech at all. I'm sure the old-time GM engineers fiddled with part values until they got something to work. Change the coil, the ignition module, etc. and you've got to recalibrate the thing. So I'd say you got lucky in that the module / coil combination worked. But I'm sure others can take advantage of your experience in that you have found a combination that works.
I have drawn a simple bitmap schematic. Unfortunately I have no place to post it. Dan, you have mail.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI