DV8, I can't remember what you know about these systems, but I begin at the the basics....
there are one or two 'vacuum relays' in the system.....with 3 3/8 ID hoses to the stem of the relay.....so the main suck hose goes to the vac canister, to suck up or down.....
then there is a little control valve, that controls the internal valve of the vacuum relay....a little diaphram on the end and a small hose, that small hose has vacuum on it, it's to suck the relay to the position of DOWN, the default is NO SUCK UP......to the lights open to the night time position....
THAT is the basics of the control logic......
your largest issue is to find the hose leaks in the system....I can say my '72 had an ancient fractured gas tank shaped canister under the left fender, beside the brakes....it was bad news, tore it out and junked it for some years, so engine had to be running to operate the wiper door OR the lights....
so no Vacuum Storage'......
I suspect you have leaky actuators for the lights, not so much the canisters themselves, but the 'witches hat' witch is the witchy part on the actuator stem seal, under the water bellows...so the actuators will not suck so good....and so the lights look wimpy when called to attention....
:gurney::hissyfit::nuts:
