Re: GM HEI...
I don't remember the Corvette module mounting any different,
but I've never tried to put the wrong one in the wrong
I hope you are appliying a full direct 12 volts to the HEI
unit, not through a resistor, and it needs a wire size of
at least 12 gauge, preferably 10 ga.
I'm trying to do this from memory:
Start by visually checking the 3 wires up to the coil.
Sometimes they get put on backwards.
Make sure both of the primary wires from the coil eventually
go to the "Tach" terminal and "Batt" or "+" terminals.
The third wire is a ground and should lead to case ground.
If all was well there, disconnect the 2 pickup coil wires
from the module. Connect an analog Voltmeter or Ohmmeter
(meter type, not digital) to the disconnected wires from
the pickup coil. Set the scale to a 10 volt scale or the
low ohms scale. Spin the distributor - this can be done
either installed in the engine or in your hand.
The meter should swing wildly up and down as it spins over
- IF the pickup coil unit is working.
If OK, re-attach those pickup wires, connect full +12 volts
to the "Batt" or "+" terminal. Connect a good ground to the
distributor housing if you are holding it in your hand - a
jumper cable around the shank works fine.
Check to make sure the 12 volts gets up to the upper primary
wires on the coil, both should read 12 volts. If not, find
Disconnect the 12 volts and reassemble the rotor and cap on
Re-connect the 12 volts.
Spin it, it should generate spark, you should be able to hear
it jumping around inside the cap, or put a plug wire on to
ground to see it spark.
If no spark, put your voltmeter on the "Tach" terminal.
You should read 12 volts at that terminal, but when you
turn the distributor it should jump up and down momentarily
as you turn it. That indicates the module is working - it's
switching current to the coil on and off.
Let it sit for a moment. Touch the module carefully with
your finger, it should be warm to the touch - or very hot,
after it's been connected to 12 volts for any length of time.
If it stays cold it's a good indication of a dead module.
It's very important to use the proper heat sink grease under
the module - else it can burn up within minutes from heat.
Use heat sink compound, not the same silicone grease you use
on plug wire ends or on electrical connectors, such as Ford
The plug end grease is an insulator, it will fry the module
even though some of the tubes of that crud say you can use
it there. Once the module gets overheated it's dead forever.
One of the holes through the module is ground, make sure
that's a good connection.
Tell us what you find, if it still is a mystery we can did a