HEI Conversion Wiring Instructions
Page created by Qute Feb 11th 2006: Back to Electrical Index
- 1 HEI Wiring Conversion:
- 1.1 HEI Wiring Conversion Needs:
- 1.2 HEI Relay Holding On After Shutoff:
- 1.3 Diode Not Necessary With This Relay:
- 1.4 Anti Hold-On Diode:
- 1.5 Troubleshooting:
- 1.6 Coil Voltage Drop:
- 1.7 Ballast Resistance Behaviour At Idle And Low RPM:
- 1.8 Ballast Resistance Behaviour At High Low RPM:
- 1.9 HEI RPM Compensation:
- 1.10 Links:
- 1.11 Terms:
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.
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.
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.
Diode Not Necessary With This Relay:
I have never had an issue with this modification. when i do it I only use a bosch rely part number 0 332 019 155 .
End of submission by MackV8. </p><p>===Implementing the Anti-Hold On Diode Modification:
===Submission by T. Dick Smith diode catalogue number Z3229 (10 amps, 1000 volt Peak Inverse Voltage). This diode is overkill but is not likely to blow on you.
===The Indicator Wire:===
The indicator wire is the thinnest wire that plugs into the Alternator. Usually marked IND.
On 85 Amp Alternators it will be marked I.
To prove you have the right wire, unplug it and turn the ignition on.
You'll notice that the charge light doesn't come on. The charge light
will come back on when you plug it back onto the Alternator or if you connect it to ground.
If you connect the 85 amp S wire to ground you'll see convincing sparks so don't do this.</p><p>(Image by T April 7th 2006)
Anti Hold-On Diode:
D+ = B+
<p>Submitted by knuckles on Fri, 10/02/2006 - 19:00.
It's straight forward to get 12 volts to the HEI coil using the original wiring on a HZ which is the wiring diagram I'm looking at now, but it's the same process/theory,maybe different colour wires on the earlier stuff like EH, HR etc.
On an HZ, working right at the switch block plug socket on top of the steering column under the dash board where the wiring loom comes out of the switch, add a 2.5cm link wire between the PINK & YELLOW wires or strip 1 cm of insulation off the wires & solder the two parallel wires together (and tape up),the PINK wire is the BALLASTED 10 Volt feed coil wire & the YELLOW wire is the momentary 12 Volt feed coil wire (which is NOT ballasted) & you will have 12 Volts feeding your coil.
Have a look at your wiring diagram specific to your model and you will see what is required and how this will work.
I have used this easy method on my 2 daily drivers and it works just like factory installed HEI, neat, fully functional and 100% reliable.</p><p> </p><p>
===Coil:===You must use the recommended Bosch HEC-716 Coil with the Conversion. This Coil and the Ignition Module are matched.===Tacho Info:===The brown Tachometer wire connects to the coil -ve.</p><p>The standard GMH Tacho will work perfectly with the Bosch HEI Conversion.</p><p>Most Tachos will work with the Bosch HEI Conversion.</p>===Diode Information:===
The Relay has been known to short internally and cause loss of Voltage.
Coil Voltage Drop:
It will not be possible to measure the Coil Voltage Drop because the Coil is only turned on for 4 milliseconds at a time. You will need an oscilloscope to prove this. Any measurement of the Coil will read +12 volts because a Voltmeter will not be fast enough to measure the drop.
Ballast Resistance Behaviour At Idle And Low RPM:
The Ballast Resistance is designed to work with Breaker Point Ignition. Breaker Point Ignition has the Coil on and off times largely equal. The Ballast Resistance becomes hot at Idle and also at low RPM. This causes an increase in temperature inside the Ballast Resistance which also causes its resistance to increase. The increase in resistance keeps the coil from failing from by reducing the Voltage supplied to the Coil by 3 Volts - That means the Coil only sees 9 volts at Idle and low RPM.
Ballast Resistance Behaviour At High Low RPM:
At higher RPM and at full RPM the Coil on time is reduced even though it is being turned on and off at a faster rate. The Ballast Resistance becomes cooler at high RPM. This causes an decrease in temperature inside the Ballast Resistance which also causes its resistance to decrease. The decrease in resistance allows the coil to provide more Voltage to be supplied to the Coil which compensates for the reduced amount of time the Coil is turned on.
HEI RPM Compensation:
The HEI Module compensates for any changes in RPM by varying the Coil ON time.