Alternator

You need to run a 12V trigger wire for the alternator to charge your battery. It must have a resistor on it — it cannot be a straight wire, so buy the right part. You can wire it into a Holley ECU or tap into one of the driver's-side fuse box wires.

Simplest Option: GM 4-Pin Pigtail

Holley's 197-400 pigtail plugs into the GM 4-pin oval alternator connector and has a 560 ohm, 1/2 watt resistor inline. Run its lead to a switched 12V source that's live in the ignition run position. You can route it through a charge light if you want a warning when the alternator stops charging.

Holley Setup

I bought a Sloppy Mechanics harness that plugs into the Holley power tap and wired it into the Holley white/red input harness, J1-A3 (the flex fuel input). Holley configuration is shown below.

Edit: set this input as digital frequency.

Holley input configuration for the alternator (Flex/Alt) signal.

Sloppy Mechanics Holley plug-and-play flex fuel / alternator combo harness

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Prices and part numbers were checked in October 2026 and can change. Always confirm with the vendor before ordering.