[KTL]

There's no headlight relays in the engine bay. That separation you see in the picture is no big deal if no damage to the wires. You can remove that harness by disconnecting it behind the fuse panel. It is a large rectangular plug that is intended to be unplugged. That bundle of wires however is very important. It's the main wiring harness connection from the chassis to the engine.

You have the correct distributor cap. No worries there. But it could need replacement. A cracked distributor cap can allow water in and short the electrical contact. I would start with the plug wires like the rest of the guys said. Plug wires can give you problems in a lot of ways:

-spark plug connector on engine can get pinholes in the insulator and allows the spark to short to the cylinder head
-spark plug connector has resistors in it that can go bad.
-water entry into boot like SpyderMike said
-damaged/aged wire insulation that allows loss of spark

The distributor cap is very easy to remove. Long flatblade screwdriver is all you need to push down and turn the spring-loaded screws free from their hook points on the distributor housing. Look under/inside the cap when you release it, and also check the rotor tip for carbon tracking and damage to the metal tip.