my 1978 ols bravada misses out when it wet outside

If you open the hood at dusk when it's damp out, you might see it arcing... I used to spray my cap and wires with a plastic like product called "Wire Dry". I would remove the cap with the wires attached, hang it up and spray everything (be sure to write down where the wires go first). After it dried, I would reinstall and give it another coat. It worked good on my rally cars and kept them firing through the water crossings.