Relays that have DC coils and that switch DC current were a big part of my job up till about the mid 1990's.

Back in the days before electronic antenna switches, I burnished a LOT of relay contacts. His burnishing of the contacts SHOULD yield a less-resistive contact. The resistance that may have built up from contamination and arcing would be the kind of thing that would feed on itself, getting worse faster and faster.

In DC circuits, arcing (and the pitting of the contacts that it causes) can be due to inductive loads (like a motor). It can also occur when the load is pulling more current that the relay is designed for.

Sealed relays perform better, since no contaminates can get to the contacts and mess them up - certainly not the case with the open-frame relays in our cars. I suspect we will see a LOT more troubles like this as the cars age.

But another cause is an armature that moves too slowly. Again, with open frame relays, anything that gets in there to impede the movement of the armature can cause trouble. His spraying of cleaner around may have done more good for the armature than for the actual contacts themselves.

I'd like to see how long this repair lasts! I am not too cynical about his repair, Dave. And again, I think we are going to see these kind of failures more and more. I think Tightd1's replacement/loaner RCB thing may turn into one of us starting a relay-replacement service. These little 12 volt relays are common, and replacing every one on the board (if you have desoldering equipment other than that damn "solder wick", which I do) should only take 1/2 hour.