“What I Learned Today,” With Jeff Smith: Ignition Power

This is the fuse box in a new American Autowire kit that will replace our 50 year-old wiring harness in our ’66 Chevelle. Not all accessory circuits are live during cranking, so it’s important to check the circuit under cranking to make sure the circuit you tap into for ignition power will be live during cranking. The two circuits marked ignition would be a good place to start but we’d still verify this to make sure.

When installing a new ignition system, always ensure the “12-volt hot” side of the feed to the system is hot during cranking. We learned this lesson after installing a carbureted LS engine in our Chevelle. We used the MSD 6014 ignition box that required a simple switched 12-volt wire to power up the system. The engine cranked over but refused to start because we had connected the switched ignition “hot” side for the ignition box to an accessory ignition circuit that was dead during engine cranking. It took us awhile to figure out why the engine had no spark during cranking. 

We had connected the MSD box to a switched accessory terminal on the fuse box that was live with the ignition switch in the “on” position, but when the key was turned to “start”, this terminal went dead. We eventually tapped into a circuit that was live during cranking which solved our problem and the engine started immediately. All ignition switches will supply battery power during cranking but this does not always extend to the fuse box, so check your connections carefully to make sure there is power during cranking.

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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