1990 Mustang Wiring Harness - Ford Mustang Forum Jul 17, 20081990 Mustang Wiring Harness 5 Tech. The correct year dash harness is your best bet. As was said above the wiring for the fuel pump relay are different between the years and the fog light / convertible top wiring are also different (if that applies to you). 1990 mustang wiring harness | eBay Find great deals on eBay for 1990 mustang wiring harness. Shop with confidence. Skip to main content. eBay Logo: 1990 Ford Mustang GT LX 302 5.0 V8 Fuel Injector Intake Wiring Harness 87 88 89. Pre-Owned. 1979-04 Ford Mustang Wiring Harness Plug Retainer Hardware Clips (Tape On) Brand New. $8. Buy It Now. Free Shipping.