Can' t get my G26 running.So I took it out of my Nieuport and mounted it on a test stand. I Have to start eliminating problems. In the plane I took the coil off the engine and mounted it to the firewall. On the test stand it is mounted to wood as well. Would that cause a problem?

The coil will need three connections:
connection to the motor for timing.
Spark plug lead
Pigtail to ground the coil to the motor. If it does not have the grounding pigtail it needs to be mounted on the motor to provide ground

dirtybird pegged it! On the G-26 mag engine, the HV coil grounds to the engine case with one of the mounting bolts. Probably best to maintain this mounting method if at all possible.

thanks I'm going to test it on my test stand with a wire to ground it. The mount I have in the Nieuport hides all but the spark plug boot but the coil needs to be mounted on the firewall.

A long ground wire to coil may emit RF. You may want to use a shielded set-up. Good Luck