Just bought a '79 and the headlights are tempermental. Sometimes they come on, sometimes not, sometimes they go off and on while I drive. The doors appear to open fully and the actuactors(?) appear rebuilt/clean. I suspect I have a small vacuum leak, if that's a potential cause. I can hear a slight hiss under the dash and the auto-tranny is not shifting very smoothly.

Do you mean up and down or light/no light?

I mean light/no light. They go up and down fine.

sounds more like a bad ground. all the vacuum does is open and close the lights.  you may also have a vacuum leak too. make sure that hiss is not the switch shorting out and possibly causing a fire.

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LIFETIME MEMBER #97
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[QUOTE=StangRay]I mean light/no light. They go up and down fine.[/QUOTE]

The "hiss" sounds like a vacuum leak, especially if you add in that the trans is not shifting properly. A vac. leak big enough to hear will definitely effect the trans operation.
As far as the lights flickering on/off, do you hear a "clicking" by the headlight switch when they flicker? If so, the headlight switch is probably bad. There is a breaker circuit built into the switch, and they will cause the lights to flash/flicker like that. It could be due to a short in one of the lights, or just a bad breaker.
I have seen some instances where people put in high powered headlights, and LED tail/brake-lights that cause the breaker to overheat and trip, but that doesn't happen a lot. A connector on the light switch that has overheated over time will also cause it...might be time to check the connector for heat damage.

Does it only do this while driving, or will it also do it just sitting still?

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Joel Adams
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I had two problems surrounding electrical on lights.  First, I had to change the switch.  I then had to take the switch back out and tighten the female connector on the red wire.  I had to tighten each side of the connector that contacts the blade as it was very loose and heating up.