So I have been fighting this dang tach for 2 days. Installing due to have the bare bones cluster. No matter where I tap, gray wire or green/or on the back of the coil rail, on the red/black stripe on #5 inj. Or on the tan wire back at distributer, IT WILL NOT READ! Is it due to me buying a cheapo off of eBay or what l??? Help please, lights up and the needle wiggles on 0 that's it!

2000 cherokee