Tremec T-56 Magnum | All-in-one Wiring Harness, with Apr 13, 2018The All-in-One harness eliminates the need for any additional equipment to operate the reverse lock out or generate the correct speedometer signals coming from your Tremec T-56 Magnum. This All-in-One harness solution is the perfect finishing touch for any Tremec T-56 Magnum conversion, and the only harness you will ever need.5/5(4)Brand: Bowler t56 harness | eBay Find great deals on eBay for t56 harness. Shop with confidence. Skip to main content. eBay Logo: 1992-1993 LT1 PSI STANDALONE WIRING HARNESS W/T56 or NON-ELECTRIC AUTOMATIC See more like this. 2008-2015 LS3 (6) PSI STANDALONE WIRING HARNESS W/T56 58X DRIVE BY WIRE DBW. Brand New.