It shouldn't really make a difference. One line is constant vacuum and the other is to supply vacuum to the headlight system. So either the port is open or it's closed. You can try to switch them around. But if driverside headlight stays up, then you have a problem at either the vacuum relay or headlight actuator. Or even a vacuum line on that side gone bad. If the lines are original they should be changed. 31 yrs. is a long time for rubber lines.

Let us know what you find.

Sarge

I think it does matter which vacuum line is on which port,I recently

changed my switch out,as I could only operate the doors with the override switch. i think ecklers sent me a defective switch as I can hear air leaking from the switch, the product help guy at ecklers said the front port on the switch closest to the dash goes down to the

override switch and the back port goes into the firewall. Can you still put up the and close the other door.

I agree with Sarge, I feel that the problem is probably with the vacuum relay, actuator or lines going between the relays and actuators.  I recently troubleshot my system and replaced the relays.  I accidently connected the lines in reverse to the left relay.  When I turned on the lights, the right light went up and left stayed down.  Turned off the lights and the right went down and left came up.  Don't know if you worked on the relays, but might check them to see if they're working ok.

Larry

If one headlight is working, the problem is not in the dash.  There is only one control circuit in the dash that splits to operate both lights further out.

Now here is the exception.  If there is a leak in the dash causing a weak vacuum signal, it may be strong enough to operate one light and not the other.  Springs, seals, and components do not always operate the same after years of use.

SO....if it's a small leak, the problem could be in the dash.  But it's not a hose disconnected or completely off.

That'll teach ya to mess with vac. lines on a Shark!!
I agree, its most likely a problem at the front of the car, not the h/light switch.

The '74 uses the front "crossmember" as the vac. reserve tank. It has three lines on it: one from the engine(vac. sig), and two that go to the actuators(1 left-1 right). The signal vac. from the lightswitch goes to the actuator relays, to switch the vac. from one side to the other on the actuators(up or down).

If the vac. lines were crossed at the relay, then one light would go up when the other came down. I suspect you may have gotten the hoses mixed up on the one relay valve. The yellow hose goes on the center nipple, and then you have a red, and a green hose, that go to the actuators. Make sure you have the yeller hose in the center, first, and then check the rest from there.
You can have a leak that would keep the one light from operating, as Ken says, if the actuator seals were weak. Happy hunting!

The relay valves are bad about giving up the ghost, also, so I wouldn't rule one out as a suspect


btw.... the colors mentioned here are just a stripe on the hoses, not the actual color of the hose, itself.Adams' Apple38653.7754398148

Recommend you go for a "Killer Light" electric system at mcspeed.com.  It will be no more expensive than replacing, once you find it, the faulty vacuum part.  I have them on my 73 and they work great, no vacuum drain, open and close rapidly together every time and even work with the engine off.  Not for a NCRS ride but they work and well. OH6A38654.7378703704