MSD Ready to run distributor wiring question
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4wd High
Joined: Apr 2024
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MSD Ready to run distributor wiring question
Looking for some info if anyone has experience with this. 1978 F150 with a new 400 crate motor on the way. Motor was built with an MSD ready to run distributor. After reviewing install instructions it is recommended to install a relay to switch 12v to distributor instead of the existing coil wire (which would be used to trigger the relay) due to the resistor wire lowering the voltage. Ordered a pertronix relay kit to install but found a note in it that a diode needed to be installed inline on the I terminal of the voltage regulator so the engine would not keep running when the key was turned off. Also mentions to watch the Batt/Alt dash light after install. My truck has a factory alternator gauge so the I terminal is not used. My question is do I need to install a diode for this configuration or not? If so I assume it would be on the red/green wire coming from the switch. Thanks for any help.
Lead Driver
Joined: Jul 2017
Posts: 9,606
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From: San Jose, CA
Yes, and with the MSD distributor, supposedly firing a hotter coil, you probably don’t need the I wire anymore anyway.
They’re not talking about the I terminal on the regulator though. They’re talking about the second small terminal on the starter relay/solenoid. The one on the left is marked with a “S“ and the one on the right is marked with an “S” for ignition.
This Brown wire is used to supply 12v to the ignition system when the starter is cranking.
This is not necessary with a relay essentially bypassing the resistor wire.
But it might still help, depending upon which ignition coil is used. Because the coil will still require the resistor wire if it’s not matched to the distributor. If it’s intended to work with 12 V, however, you will not need the resistor wire for the coil any longer either.
They’re not talking about the I terminal on the regulator though. They’re talking about the second small terminal on the starter relay/solenoid. The one on the left is marked with a “S“ and the one on the right is marked with an “S” for ignition.
This Brown wire is used to supply 12v to the ignition system when the starter is cranking.
This is not necessary with a relay essentially bypassing the resistor wire.
But it might still help, depending upon which ignition coil is used. Because the coil will still require the resistor wire if it’s not matched to the distributor. If it’s intended to work with 12 V, however, you will not need the resistor wire for the coil any longer either.
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