service light on, 99 Suburban, viper 560

Check your tach signal wire and make sure it is not touching any metal or another wire in the coil harness.  The code it is throwing has to do with the ignition module (Coil) or misfire (coil pack).  This would be directly linked to the tach source you are using.  I always use the white eire found at the coil on the passenger side of the engine near the air cleaner.  There are three wires in the harness iirc, use the white one.

I grabbed the tach wire from the black plug labeled white on the drivers side fender. It was a white wire. The code is (P1345)----"factory ignition module and or misfire". It runs fine, no shaking or loss of power. Everything seems fine except for the SES light. Should i try to tap into the tach at another location?

I would tap into the coil harness itself.  there are three wires.  One white, one WHITE/ black, and one pink.  tap the white wire and see what happens.  the coil is on the passenger side of the motor, right below the air cleaner above the walve cover.  Be careful because there is a sensor harness right next to it.  Just look for the coil plug wire running to the disty and trace that to the coil.  You should see the harness on the top front (toward the front of the vehicle).