Haynes is correct.
Never had that problem but your symptoms might be here.
http://www.classictruckshop.com/clubs/earlyburbs/projects/trouble/ignition.htm
More than you ever wanted to know about ballast resistors.
Whatever you say to the mechanic, never, never, never tell him you suspect that you’re low on 710. You’ll get taken for sure.
;>)
LOL!
I guess if he tells me he needs a left-handed monkey wrench, I’m in real trouble, yes? ;o]