I'm attempting to set timing on a 1975 360 but light flash is jumping back and forth about 16 degrees. Never seen this before. Could my light be faulty? Has anyone seen this before? BTW I'm using a cheap Harbor freight light.... Any comments or ideas to fix this thanks.

 

Worn out timing chain and gears or a Distributor advance problem

 

Ive seen a cheap timing light get triggered by the wire next to the one it's on...