Tach wiring for 99+ Vortec/LS

Some PCM tach signals are too weak for some aftermarket tachometers. Connect a 1k Ω (brown/black/red) resistor between the tach wire and a fused key-on 12V source: one end to the tach wire, the other to fused 12V+. The tach wire is Pin 10 on the RED PCM connector for 1999–2002 vehicles and Pin 10 on the GREEN PCM connector for 2003–2006 vehicles.