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so my dad and i installed a four barrel on my 390 and then my headlights wouldnt open, however i found the vaccuum line was off, and this fixed it. the issue began again a few weeks later. All lines are accounted for and connected, has anyone else had this problem?
 

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Vacuum test the complete system (motor(s) and vacuum tank) with a hand held vacuum pump.
 

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Get the vacuum diagram for your car, as it doesn't sound like it's hooked-up right. When you lose vacuum, the doors should open as a safety measure. As long as you have a leak-free vac system and your diaphragms are good; they are easy to keep working fine. If your diaphragm is shot, some models are cheap to repair, and others a small fortune. In that case go electric.

David
 

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68's do not open with vacuum loss, that was a federal mandate beginning in 69. I'll try to lay out the vacuum routing as best I can for you according to the shop manual and OEM hose color stripes (if you can use a bit of colored electrical tape to help identify them).

Orange (1/4") = From intake manifold to the check valve (1 in, 2 out on top of the firewall)

White (1/4") = From the check valve to the vacuum reservoir on the driver side fender

White (1/4") = From the check valve to a 90 degree 1/4" hose connector, then through the right most position of the dash panel junction box to the middle position on the headlamp switch distribution valve.

Green (1/4") = From the rearward (as installed) position on the headlamp switch dist. valve through the middle position on the dash panel junction box to a 90 degree 1/4" hose connector, then to the top of the cover control motor behind the front bumper.

Yellow (1/4" to 1/8") = From the forward (as installed) position on the headlamp switch dist. valve through the rightmost position on the dash panel junction box to a 90 degree hose reducer (1/4 to 1/8), then 1/8" hose to the bottom of the cover control motor.

West Coast Cougar Classics (just google them) makes a replacement cover control motor and check valve for a small fortune.
Local autopart stores have replacement headlamp switches for about $30
The vacuum reservoir can be replaced with a universal brake booster reservoir from summit, jegs, or comp cams easily enough ($40-$80) or you can try resealing yours with some RTV and replace the check valve with a new one if it has one I would imagine.
 
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