all the lights on my 1985 f250 flicker,i have checked all the grounds every thing seems to be in order?
Do the lights flicker really fast, slowly or spasmodically?
I’m thinking a faulty alternator.
Make this another vote for a failing alternator.
That is usually a sign of bad diodes in the alternator as the others stated. Bad diodes cause excessive ripple voltage so the lights flicker.