Originally Posted by
Whopity
The reason that radios and avionics are turned off is to protect them from the high voltage back emf that appears when first connecting a DC motor (the starter). Most modern avionics have internal protection but some older equipment does not. Bulbs are not susceptible to such transients.
But even if the modern avionics are protected, why risk it? Leave them off, and you can't be proven wrong about how good the avionics internal protection is. (The only time this should be a problem is if your airport requires a call for engine start, but that's pretty rare).
I agree about the lights.
G