The headlights from '81 to '85 were the quad rectangular style. Ordinarily, these do a good job and are considerably better than the plastic headlights used on '86 and newer model 240s.

Check the connections (and connectors) in the cables going to the headlights -- they're known to become corroded and grime-filled, which creates resistance. Check the plugs at the bulbs. Most importantly, check the ground connections, which are a common source of resistance.

Any corroded or crummy connections will create resistance which limits the current flow through the bulbs and they become yellow and dim.

Use a good voltmeter and measure the voltage at the bulb socket with the lights on and plugged in and the engine idling. Put the black lead to a solid chassis ground. You should measure at least 12 volts at the "hot" side and essentially 0 volts at the ground lug of the bulb. If you measure more than about 0.25 volts (1/4 volt) at the ground lug, then you have resistance in the ground lead. If you measure less than 11.5 to 12.0 volts at the "hot" side, then you have resistance in the power feeding to the bulb.

Do this with the engine idling -- you should measure at least 13 volts across the battery. If you don't, your problem might be alternator related (or the wiring to it).

"...one of the lights looks darker than the other..."

It might be time for 4 new bulbs. Be sure to get halogen bulbs. I like the Sylvania brand.
--
Don Foster (near Cape Cod, MA)