HEI Conversion Wiring Instructions

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Page created by Qute Feb 11th 2006:

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Holden 149 engine with original Breaker Point Distributor. Note there is no Ignition Module on the Distributor. Click to Enlargen. Photo by Peyser.
Holden 202 Six with HEI conversion in HR. Note that the Distributor has the Ignition Module mounted on the offside. Click to Enlargen. Photo by HQ_SS.

HEI Wiring Conversion:

HEI Wiring Conversion Needs:

HEI Coils and Ignition systems must be powered with +12 volts to work properly. Powering them through the original wiring will mean that the Ballast Resistance will still be present. The Ballast Resistance must be removed from the circuit to make sure +12 volts reaches the HEI system.

If the Ballast Resistance is kept in place, the Engine will misfire at higher RPM because the Coil's increased current demand will cause an increase in voltage drop across the Ballast Resistance. The Coil will then see reduced voltage and its output will be reduced.

The Relay Method:

The Red Wire in the below diagram is 3.0 mm.

The Relay method of wiring the Bosch HEI Ignition System. Image by T. Click to Enlargen.
The Starter Tap is where the thick black Wire is bolted. Photo by HRAmbo. Click to Enlargen.
Bosch HEI Distributor as fitted to Blissy's 186S Engine. Photo by The Red Baron.

HEI Relay Holding On After Shutoff:

Submission by T April 1st 2006:

Sometimes an HEI Relay can be affected by Back EMF flowing from the Alternator
back up to the Alternator Indicator Light when the Ignition is turned off. Placing a 6 amp diode in series with the Indicator Wire to the Alternator will cure this.
The current through this wire will be less than 1 amp. I recommend using massively overrated Electronic components in Cars at all times. You will be able to buy a 6 Amp Diode from Dick Smith very cheaply.
Cut the Indicator Wire at a convenient location somewhere under the Bonnet.
Cut the Diode legs until they are about 0.5" long. Using a blue Crimp Connector, crimp the Diode so that the white Band on the Diode is nearest the Alternator.
If there is no white Band on the Diode, then the Diode will be shaped like a bullet. Connect the wire so that the Bullet is travelling towards the Alternator.
The Diode will allow currrent to flow to the Alternator, but no current to flow back.</p>

End of submission by T.

Detailed HEI Relay Holding On Explanation by BF6379:

HEI relay hold-on
Submitted by bf6379 on Fri, 31/03/2006 - 23:56.
T,
The wire that you speak of not only provides start up excitation but also controls the alternator warning light (battery light) on the dash. The IND terminal on the alternator that this wire is connected to is fed from an auxillary output of the alternators 3-phase rectifier that primarily provides field current to the armature winding via the internal or external regulator.
When the engine is running and everything is normal the alternator IND terminal supplies +12 volts to one side of the light and the ignition switch supplies +12 volts to the other side of the light. No difference in voltage across the light, no current flows and the light does not glow. If the alternator fails then the voltage at the IND terminal will drop towards zero volts and current will flow through the lamp making it light up.
When you switch the ignition off to stop the engine, the IND terminal continues to supply +12 volts to the light until the engine stops spinning. The other side of the light (which is normally supplied +12 volts from the ignition switch) has a path to ground via the ignition coil and any other accessories connected to the "on with ignition" output of the ignition switch.
This is why the alternator light comes on briefly when the engine is switched off. The current flowing through the coil via the relatively high resistance light bulb is not enough to allow the coil to generate a spark and keep the engine running, the engine stops and the IND terminal of the alternator falls to zero volts.
If the coil is disconnected and a relay wired in its place then the current flowing through the light to the relay will be enough to hold the relay on. Bosch 30 amp relays only require about 20 milliamps to hold the contacts closed. If the relay is on, power is being supplied to the ignition and the engine keeps running, the IND terminal supplies +12 volts to the relay via the light, the relay stays on. Vicious circle.
Applying another load, like handbrake light or reversing lights provides another path to ground and takes some of the current away from the relay, allowing it to turn off.
Brett.

Diode Not Necessary With This Relay: