I have a new (to me) 76 El C, and am going thru it and
shaking out the problems one by one. Tonight I checked out
the headlamps, and found the low beams came on, but when I
hit the dimmer switch, the left high beam came on with the
low beam, but the right side low beam went off and the right
highbeam didn't come on either. I pulled the right side
high beam bulb loose, and the low beam came on, but very
dim, in fact flipping back to the low beams now the high beams
are both just barely on (only see it in the dark), like
there is some voltage leaking to the high beam circuit.
I checked the dimmer switch, but it tested OK. I went
ahead and put a new switch on anyway, no improvements.
Harness appears to be unmolested, except for Right side
low beam has no plug (3 bare terminals) on the low beam
bulb. Bulbs all look O.K. (halogen sealed beam). Does
it matter on the 2 terminal high beam bulbs which way
the terminal is attached? I tried both ways on the right
side, no difference found. Voltmeter on high beam circuit
shows about 5 or 6 volts.
Any suggestions?
Thanks
Jim

Yoor problem is either connections at the bulbs or the ground wire. Ground wire comes off bulb and it bolted to rad support. (black wire) Make sure the connectors fit tightly in the bulb terminals and the ground wire is clean and bolted tight to bare metal (use a star washer)

Thanks,
I had to rework the ground leads on both sides, replace
a terminal in the RS Low beam plug from an old harness,
and clean all the terminals in the plugs on the RS. So,
not only several bad grounds, but several bad connetions
too. Works like a champ now.
Jim