TMCP #179: John Spears from Speartech – LS Engine Harness Swaps Made Easy!


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A clean and easy harness application from Speartech. This particular one is a 58x specific unit for a Gen IV LS engine.


This week’s interview is John Spears, founder of SpearTech Fuel Injection Systems. John has always been a car nut and at a young age decided that he should pursue a career in automotive. He graduated from Indiana University-Purdue University Indianapolis, and landed a job at Delco-Remy in Indiana as an electrical engineer in the ECM labs. He was interested in putting LS power into older cars of his own and used his expertise to create simplified wiring harnesses to pull it off nicely. As it always goes, after awhile started helping others do the same and he eventually  got to the point where his evenings were all tied up with his “side projects.” When the time came it was a simple jump from the garage to the start of SpearTech Fuel Injection Systems.

Extra wiring removed from a stock LS wiring harness
Extra wiring removed from a stock LS wiring harness

SpearTech offers multiple different new harnesses for LS engine swaps as well as offering a rework service to convert production harnesses into something a muscle car enthusiast can use in their vehicle. John can even build custom harnesses for special circumstances such as remote mounted ECM’s or special fuse block requirements.

Since a factory harness contains everything from wiper motor relay wires to coil pack connectors, eliminating a lot of extra wiring leaves a nice streamlined harness for a clean installation.

LS engines have two different kinds of crankshaft reluctor sensors and John explained to me that these sensors make all the difference in which harness package someone would need to purchase. SpearTech makes harnesses for both the older 24X (Gen III) and newer 58X (Gen IV) tooth reluctors. These slight differences can make for an unhappy customer if they do not pay attention to these details!

We also walked through some of the features of SpearTech harnesses, one of which is the ability to interact directly with electronic transmissions.  SpearTech has also developed a way to “tap up/tap down” shifters and capabilities as well, and they find that the majority of the customers performing engine swaps typically choose an automatic transmission.

We also touched on ECM related features, such as the removal of engine security, the addition of cruise control, and a host of other items. Speartech also offers ECM reprogramming, or can sell you the equipment to reprogram an ECM on your own bench top!

Most of you in the audience know that I truly geek out on engine control topics, and John didn’t disappoint. I hope you’ll find this interview as helpful as I did.

Thanks, John!

-Rob Kibbe


This interview sponsored by our pals at National Parts Depot – your premier source for muscle car restoration parts!



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