HEI primary winding is not connected to ground. Primary coil current must pass through a couple of resistors and a Darlington before it reaches ground by way of the module hold down screws.

I have my HEI wired with the original 6 cyl. 1.8 ohm ballast wire. Voltage drop across the ballast is 2 V. With 14 V charging voltage before the ballast, it still has an honest 12 V at the coil.

2V/1.8ohm = 1.1 Amps.

I did at one time temporarily wire a 3 A fuse in the line and the engine started and ran fine without the fuse blowing. I didn't actually drive it because I was just using jumpers.

If the HEI used that much current I would have to get a bigger alternator.
My '67 GMC has the original 37 Amp 10DN with external regulator.
Right now it keeps the battery fully charged and it has to keep up with the HEI, electric radiator fan, Climate Control AC, tecumseh trailer brake controller and small CD stereo.

'67 GMC 3/4 292 4spd