I spent a hot afternoon rewiring a 40' flatbed trailer that must have had 3 dozen Scotchloks on it. No wonder the lights didn't work half the time.
They used to be big back in the day of Windjammers and early Goldwings with aftermarket lights. Virtually every electrical problem was because of Scotch-Loks. Easy wiring for unskilled people but guaranteed to cause problems eventually.
Actually, if you smother them in silicone grease, you can get a couple extra years out of them before the wiring goes to hell.