05 600 sdi tach not working, any ideas?

[MN_MXZ]

I picked up a 05 600 sdi renegade and the tach is not working. Everything else works fine. The tach works fine in my other sled so I know that the tach is good. I have checked all of the wiring from the ECM to the speedo and tach and I have continuity on all of the wires. I'm not sure what else to look at. When I press the RER button before I start the sled the tach vibrates and it lights up as it should. Does anyone have any ideas? How can I tell if the RPM signal is going to the ECM? Is there any voltage measurements that I can take? Any help would be great.

Thanks,

Scott