CEL 21 help

[fico]

S13 into S13 red top and im getting cel 21
21 - Ignition signal in the primary circuit is not being entered to the ECU during cranking or tuning
anyone know what to do what to check? help?

[projectRDM]

Black/white to the CAS, does it show 12volts? Start there.

[fico]

any other help?