Looks like arcing across the contacts. An inductive load like a coil or a motor can cause this kind of arcing, a diode will lessen the arc. Could be the diode across the motor/coil is shorted, it can take out the transistor and relay contacts if not corrected. I'd track down the load that the relay is controlling and check the diode.

I dont want to muddy the waters here but the contacts that are burning are probably pins 2 + 6. If so the yellow/violet wire leading to the solenoids for 3-3bank solenoids and a ball locking kicker are involved. The op replaced a coil, was it one of these? Each of these coils has a diode in series with it (d33, d35, d39, and d41) after each diode is a transistor q32, q24, q23 and q22. If youve replaced one of these coils and one of these transistors then my next likely suspect is the corresponding diode.

After you've replaced the replacement relay that is

And f4 will stop the glow

Whoo Jackpot!!
I will look at the schematics asap to find a diode value.

Diode = mr501

If they all show reistance in both directions and your soldering skills are good I'd replace them all. The transistors are the return for the coils/flashers. With a bad diode you will backfeed current through the diode and short will happen across the normally open contacts on the relay when the relay coil pulls in. Cooking the coil probably killed the transistor and the diode. If the new coil is still good, chances are replacing the relay and diodes will fix the problem, the transistor should still be ok. But check it nonetheless.

I would think the contacts on that relay are probably toast. Pins 2 and 6 should have no continuity between them, pins 4 and 6 should be closed while the relay coil is de-energized. If you get high resitance on 4-6 or a low resistance on 2-4 then the damage is done. If the contacts check out fine you should be ok.

Pull the relay, power up the game check voltages at pin 2 and 6. Pin 6 should have + 50v. Pin 2 should have 0v ( or close to it). Report back.

Also make sure all of the diode bands are facing the correct direction. One reversed bias diode would explain everything.

Hmmm, question..... The replacement relay you bought. Was the coil voltage ac or dc? Contacts opening closing 60 times a second might draw a bit of an arc too.

Pin 4 should have 0v as its not used in the game. These are the voltages read on the socket, not the relay itself so voltages read are what are expected. Next I would check voltage between 7+ 8 while game is energized and started.

Also with game startedand relay out check voltages at 2 and 6

no worries, I charge almost $100p/hr fixing machines that put people to work, least i can do is volunteer to help fix machines that keep people from work! . Keeps me from getting beaten up

All of those voltages look good. I would pull f4 and put your relay back in. Start a game, measure the voltages on both sides of the pulled fuse holder.

That all sounds good! Have you tried the game with it all put back together since changing the diode? I'd try it, with my hand on the kill switch of course. Failing that I would disconnect the yellow/violet wire from each of the above mentioned solenoid coils, turn the game on what happens, if good, add one coil at a time powering on between try's. We'll track it down.
Ok, literally sitting on the tarmac with the Stewardess glaring at me. Going to have another Baldwin episode here
Good luck. I'll check back later.

Ok, make sure when you are disconnecting the coils that you are disconnecting the yellow / violet side and that once the wires are off of the terminal you reconnect the wires together while they are off of the terminal when you turn the game on. I would do all 4 coils at the same time, keeping all of the wires together (3 drop targets and kicker) and then add them back one at a time starting with the kicker.it should be the only one with a single yellow/violet wire.
If arcing continues you'll need to look at q22,q23,q24,q32 transistors again. I would also go ahead and replace that relay too. A pitted set of contacts or contacts not seating properly will draw out an arc too.