Cabin lights intermittently working

‘78 trawler—some Of the cabin lights onboard aren’t working and I can’t nail it down. I’ve replaced some of the dome lights over the years and they just seem to work intermittently. I have a few ideas on why that is but I can’t nail it down. The gauge of the wire onboard is much thicker than the wire gauge on the new lights, therefore it takes a wider butt connector to envelope the original wiring inherent onboard. Maybe the narrower wire on the new lights isn’t coming into full contact? there are a few lights that I haven’t replaced and they turn on and off just fine so it’s something I’ve done. My wife suggested using some battery terminal lube before sealing the butt connector but i just don’t think that would do anything as that’s meant to prevent corrosion. Please help! This is driving me nuts!