Intermitent Headlights

[Tynee]

Buddy of mine just bought a '71 Jimmy (That's right, we managed to make his wife mad at us both in one purchase. It was my fault he bought that "old redneck truck"). Anyway, when we went to check it out, it had one headlight out, no big deal, just a burned out bulb. We picked one up, then turned the lights on to make sure we were replacing the correct bulb, and now the one that was dead is the only one that works. Turn off, then back on and we're back to just having the original one dead. Wiggle the connector plugged into that one and all 4 headlights light up.
I followed him home from buying it, and his passenger side brake light also only works sometimes. He just left me a Voice Mail saying he has NO headlights now. I suggested to him that he check out the grounding, but when he asked me where all to look, I wasn't sure. Can anyone tell me where to tell him it should be grounded? Also any other possible causes would be nice.