GM and After-market Ignition Interfacing

A Connection Diagram for Ignition

Allows optional stand-alone operation with 5v pulse out, or ECU advance control by changing ERBG connector.


Introduction: In order to use the GM ignition unit, it requires a magnet/coil input from a GM distributor or equivalent. This solution using a 5v virtual ground allows you to use an after market electronic ignition kit to serve in place of the magnet/coil pickup as an alternative to machining the distributor to accept a GM coil and magnet.

E: EST advance/retard pulse from ECU.

R: Reference pulse from ignition.

B: Bypass. ECU applies 5v, module then accepts pulses at E instead of internal limp/start mode.

G: Ground

C: Coil -

+: +12v

N: Negative pickup input

P: Positive pickup input.



  • Pickup can be an after-market points-replacing kit, or just points.
  • Pickup pulls P terminal to ground when activated.
  • Pickup lead used for P was originally intended to connect to coil -
  • Resistor pulls P terminal up to 12v.
  • N terminal is held at 5v, as a virtual ground, allowing P to swing below.
  • Coil and ignition module from 1990 Chevy Astro van in this example.
  • Many other GM ignition units and coils will work from the 1986-1994 era.
  • Some points-replace kits overheat if left on, engine not running.  This solves that problem.