Headlights refuse to retract, 1974 car with headlights that refuse to retract Options

[Jezibel]

Main lighting switch raises lamps, lights up, but pushing switch back in fails to lower the lights.

AI says 1) Check fuses for failed or faulty fuse; 2) check headlight relay on fuse-box backside; 3) check grounds; 4) check headlights switch for possible corrosion on contacts.

System was working fine last week. It just decided today to not lower the lamps.

I have a replacement main lighting switch on order, also several Bosch 5-pin relays, and all the fuses check out OK (no corrosion on fuse block contacts.

I lowered the headlights manually, using the motor-end knobs, per the protocol, but it irritates me to not be able to immediately fix this apparently quite common problem on my '74 1.8 liter.

Any helpful suggestions, other than the cited "4-most likely causes' AI pointed out, above?

Thanks in advance.

[fixer34]

This from the pelican article:

"The first step is to determine in which electrical system the problem is located. An important clue is whether both headlights are affected, or just one. If both headlights are affected, the fault is highly unlikely to be caused by a bad motor or a bad relay.... it most likely is in the part of the system common to both headlights."

If both headlights go up when the light switch is pulled out, but NEITHER go down when pushed back in, it is something in common such as a power feed.
The relays are independent and only drive one motor.

Need to get the multimeter or test lamp out and check the power circuits that run to both motors. I think the wiring diagram notes them as GY and R (from fuse 12)
GR-BK to the relays could also be suspect.