Author Topic: Need help with Mallory Unilite HEI distributor install.  (Read 5206 times)

Old Man

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Need help with Mallory Unilite HEI distributor install.
« on: June 28, 2007, 04:53:55 AM »
I bought a Mallory Unilite HEI distributor to replace the points distributor in my 69 350. The first warning in the installation instructions says "Before installing the Unilite distributor make sure that your vehicle is equipped with an ignition ballast resistor (or loom resistance wire) in the wire between the ignition switch and the coil (+) terminal. Check a service manual for your vehicle to locate the ignition ballast resistor ( or loom resistance wire)." I looked in my 1969 Chevrolet Chasis Service Manual and could not find a reference to the resistor anywhere, I probably missed it. Can anybody tell me if the 69's had such a beast and how do i locate it if it does? Thanks

rat pack

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Re: Need help with Mallory Unilite HEI distributor install.
« Reply #1 on: June 28, 2007, 05:18:08 AM »
It is the white cloth covered wire with purple & orange tracers through it that goes from the fuse panel to the coil. If your harness has not been modified it will also be attached to the yellow wire going down to the starter. It is show in the AIM under the engine compartment wiring.......RatPack.........
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Old Man

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Re: Need help with Mallory Unilite HEI distributor install.
« Reply #2 on: June 28, 2007, 05:02:33 PM »
It is the white cloth covered wire with purple & orange tracers through it that goes from the fuse panel to the coil. If your harness has not been modified it will also be attached to the yellow wire going down to the starter. It is show in the AIM under the engine compartment wiring.......RatPack.........

Thank you RatPack, I'll have to check the AIM when I get home this evening.

rich69rs

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Re: Need help with Mallory Unilite HEI distributor install.
« Reply #3 on: June 28, 2007, 07:58:06 PM »
It is the white cloth covered wire with purple & orange tracers through it that goes from the fuse panel to the coil. If your harness has not been modified it will also be attached to the yellow wire going down to the starter. It is show in the AIM under the engine compartment wiring.......RatPack.........

There are two primary circuit wires from the ignition switch that connect to the + terminal of the coil; one wire for applying a full 12 volts for starting and a second "resistance" wire which reduces the voltage to the primary side of the coil when the engine is running.  The wires to the distributor and the tach lead (if you have a tach) connect to the negative (-) terminal of the coil.

When the ignition switch is in the start position, the ballast resistance (or resistance wire) is not in the circuit, and a full 12 volts is applied to the primary winding of the coil for starting.  After the engine starts and the ignition switch is in the "on"  or "run" position, the ballast resistance wire is now in the circuit and the other wire is not.  The ballast resistance drops the voltage from 12 to somewhere around 7-9 volts, enough for running while saving wear by reducing arcing across the points in the distributor.

Attached pic is typical.  It shows a ballast resistor in the "start" circuit.  Sometimes GM used a ballast resistor and in other applications GM used a special resistance wire of a given length to create the required resistance to drop the voltage from 12 to 9 or so.  Not sure of other years, but my '69 RS has the resistance wire which is easily identified by the cloth like material that covers the OD of the wire as described above.

For my ride, I converted the orignal distributor to electronic via the Pertronix unit - so I didn't have to worry about egine to firewall clearance issues.  Some previous posts on this forum have discussed various HEI distributors that were too big to fit without using the "beat to fit, paint to match" approach on the firewall to get enough clearance.  Just FYI.
« Last Edit: June 28, 2007, 08:14:38 PM by rich69rs »
Richard Thomas
1969 RS

Old Man

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Re: Need help with Mallory Unilite HEI distributor install.
« Reply #4 on: June 29, 2007, 03:42:18 AM »
It is the white cloth covered wire with purple & orange tracers through it that goes from the fuse panel to the coil. If your harness has not been modified it will also be attached to the yellow wire going down to the starter. It is show in the AIM under the engine compartment wiring.......RatPack.........

There are two primary circuit wires from the ignition switch that connect to the + terminal of the coil; one wire for applying a full 12 volts for starting and a second "resistance" wire which reduces the voltage to the primary side of the coil when the engine is running.  The wires to the distributor and the tach lead (if you have a tach) connect to the negative (-) terminal of the coil.

When the ignition switch is in the start position, the ballast resistance (or resistance wire) is not in the circuit, and a full 12 volts is applied to the primary winding of the coil for starting.  After the engine starts and the ignition switch is in the "on"  or "run" position, the ballast resistance wire is now in the circuit and the other wire is not.  The ballast resistance drops the voltage from 12 to somewhere around 7-9 volts, enough for running while saving wear by reducing arcing across the points in the distributor.

Attached pic is typical.  It shows a ballast resistor in the "start" circuit.  Sometimes GM used a ballast resistor and in other applications GM used a special resistance wire of a given length to create the required resistance to drop the voltage from 12 to 9 or so.  Not sure of other years, but my '69 RS has the resistance wire which is easily identified by the cloth like material that covers the OD of the wire as described above.

For my ride, I converted the orignal distributor to electronic via the Pertronix unit - so I didn't have to worry about egine to firewall clearance issues.  Some previous posts on this forum have discussed various HEI distributors that were too big to fit without using the "beat to fit, paint to match" approach on the firewall to get enough clearance.  Just FYI.


Thanks Rich that's some good info. I found the resistance wire wrapped in some form of white cloth attached to the + terminal of the coil as stated above and the other wire also. After I finish installing the Mallory unit I intend to send my points distributor in and have it modified to HEI. I think I'm pretty lucky, so far my car has been pretty close to stock in all aspects, seems to make things alot easier on me.