<What kind of signal is on the CAS line
If memory serves, it's 0 to 5vdc square wave.
<Could it go through a relay safely?
Yes, but I'm not sure where you are going. You
thinking normally closed contacts to OEM CAS, norm open to
backup CAS? You still have to manage angle offset. Would be
unfortunate to have moisture in relay or turbulence disrupt CAS.
Likely not going to end up with safety improvement. Good
creative idea though.
The rotary engine CAS is set up on a bracket near the front pulley.
I was envisioning a system where you had a sensor in exactly the
same spot on the other side of the toothed wheel. You might need an
offset alternator pulley to make room for it - but then you don't
have to worry about angles/offsets. It's just a second sensor, ready
to go - flip a switch and try an engine restart. If relay
reliability was a concern there are always SSRs or even just good
switching transistors...