Good questions. It looks like a fun game, but I’ve never played one myself.

1. Maybe a 3-5 ball feature diff, diagram? (As I recall they do light in pairs)

2. Yes, on the underside of the pf there is a large bank, should be a relay per rollover. a make break switch on each relay will move the lit lamp. lift your pf, check the label on the bank, if label is missing manually actuate each over and watch the bank and make each relay with a sharpie. bank swings open to allow easier access to the contacts. You will need to put the pf upright leaning against the head to allow you to open bank..

https://www.ipdb.org/showpic.pl?id=2160&picno=41807

3. On my Ks&Qs the hole lighting for special is controlled by the 0-9s unit in the head. Im sure SA is the same

https://www.ipdb.org/showpic.pl?id=2160&picno=41809

On my machine, once you roll over a colored number, that same number on the vertical column lights up. I don't know/remember the scoring for the holes, but I know it increases with the number of lit numbers in the vertical column.

The lights in the holes illuminate when all four numbers for that column are lit. It rotates from hole to hole with the 0 to 9 unit (As mentioned above).

Most likely, you have dirty/bad contacts on the relay bank that are causing issues. One word of caution - when putting the bank back in, make sure there is no twisting of the assembly. I've had issues that suddenly cleared up on Gottlieb machines when I reseated the relay bank.

Pop bumpers often share a relay, probably as a cost savings measure. On Sing Along the red bumpers share the E relay and the yellow bumpers share the D delay.
Sing Along pop bumpers (resized).jpg
Typically the pop bumpers that share a relay are far enough apart so that they have time to recover to kick a ball that travels between them. If they're too close together the 2nd bumper might not recover fast enough to kick the ball after the 1st bumper fires.

Make/break switches on the trip relays like these control whether the target or hole lights are on:
Sing Along hole lights (resized).jpg
If the target light goes out you know the relay tripped. If the hole light doesn't come on the issue is likely with the normally open half of the make/break switch.

I think the holes score 10 plus 10 for each light that's on (assuming your lights are working properly).

The holes light when you get all the numbers of that color. They cycle on and off as 1 point or 10 points are scored. They are also “weighted” from left to right. The left holes are lit more frequently than the right side - I guess assuming that the kickers are going to allow you to hit the right holes more frequently. I can pull out the schematic if you need more specifics

Dave

Only one hole at a time can be illuminated.

I never noticed my machine activate the hole kickout on startup. The machine may not be seeing the ball in the launch area.

Pinball Resource is the place for Gottlieb parts. He is old school and direct - be prepared. By old school, I mean he only accepts checks, and the invoice comes with the parts. In other words, he sends you the parts, you send him a check. First order I think is limited to about $100, and if you pay promptly, then there's no ceiling on reasonable orders. Tell him what machine you have, and if you have part numbers, that's better yet.

Part numbers are in the Gottlieb parts catalogs which aren't available online.
PBR has rebuild kits for pop bumpers at:
http://www.pbresource.com/pfbumpb.htm#rebuild
and flipper rebuild kits at:
http://www.pbresource.com/rebuildkit.html#KT-GFLIP01

Why? They should be your primary resource! Pun intended.

As a final note: my sing along does not fire the hole kicker upon startup. The red pops activate together, as do the yellow.

Hole scoring starts at 10 points, and increases an additional 10 points for each number in that column lit, so if you have two numbers in the column, you get thirty points.

Only one hole at a time can(should) be illuminated for a special. It will only illuminate when all four numbers in the column have been achieved.

Hope that answers all your questions. This is a grail pin for me, it’s the first one I remember playing, and the first machine to suck my pockets dry.

Just picked up a much forgotten Sing Along, doing a stripped down pf cleaning above and below. Noticed an inordinate amount of chalking/oxidation on all the bayonet sockets. Can anyone tell me what causes that?

Also, this is the 1st game I remember that doesn't have a on/off switch, either under cabinet or side of head. No sign of one removed. How have other owners decided to manage this?

I love bringing a game back from near death. It's nice to bring Gottlieb back into my collection. Appreciate anyone's input in advance.

The bulb sockets can be cleaned with CLR, as long as the inside is clean, the sockets will work regardless. Lots of work to “fix” something most folks won’t see.

There is no on/off switch - you kick underneath and the kick switch turns off the machine - kick it toward the center of the playfield around the yellow and green 2s. To start the machine, hit the credit button or coin it up.

Thanks @billc479, shutting the game off by hitting the underside is vaguely familiar from when I had games of this era in the 1970s. Been so long I just forgot.