You don't have to modify anything, just use a two prong ballast in place of the 4 prong. Not sure why they wired a 4 prong setup in a 71 harness, should of done the two prong. below shows how to set up the two prong, color codes should be the same.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.