It’s common for the relays to appear like that. In the case of the link, I’m hedging my bets on that being caused by too much resistance in the earth circuit and that creates the heat. That is rectified by removing the parts described and cleaning them up.
Good to get a before and after measurements.
If you remove the relay, have the power off. No keys in.
Pin 87 & 87a will be the earths (usually). So the multimeter probe in one pin and touch the other to the body or better still, to the hard to reach earth point behind the battery.
Here’s the important tools I used.
The wire brushes (cheap to buy from Supercrap or Bunnings.) I really should get some new ones.
The multimeter. In the setting I have it turned to, it makes a sound if the pathway through the wire is good. It will also give a measurement on the screen of how much resistance is in that pathway.
Those relays cost about $15 on eBay or
sparesbox.com.au