Only runs 40 Degrees advanced

I have been trying to sort out a tuning issue lately and doing a lot of dist recurving.

Yesterday I installed a distributor and when I checked the timing it was at 40*. ! But running ! I immediately thought of this thread...
1st thing I did was to flip the rotor 180*....no go.
Next thing was to disconnect/reconnect my timing light. Bingo!
My timing light start displaying the wrong rpms from time to time and I have to pull the plug and reconnect it. Like resetting it.

Time for a new Dial Back Light. Or just use one of my other oldies..