Great Plains Electronics is as great source. Not sure if he has all of what you need though.

I read a vid1900 post that said to replace .100 pins with .156 pins on old Bally and Stern boards as the .100 are unreliable.

I buy from Great Plains Electronics G-P-E some people buy from Digikey or Mouser.

You can search in this area on the Pinball Life website for the connectors that you might need:
https://www.pinballlife.com/molex-crimp-stuff-connectors-and-parts.html

I'd start with digikey, since they're Canadian and can ship to you cheaply overnight
Then GPE, since this is Ed's specialty.
Then the usual suspects for all parts pinball.

Big Daddy has a lot of the Bally stuff, but some of their connectors have to be trimmed to fit. You just can’t find some of this stuff anymore.

https://www.bigdaddy-enterprises.com/

I’m happy to test the Medusa head harness once it’s ready!

.100 size connectors - 12, 15, 16, 17, 19, 23, 25, 28

All of these can be found here --
Genuine Molex (larger sizes no longer available) --
https://www.greatplainselectronics.com/products.asp?cat=68
Generics (all sizes available Including the elusive 25 and 28 pin plugs.) --
https://www.greatplainselectronics.com/products.asp?cat=164

.156 size connectors - 2, 8, 9, 10, 15, 18, 20

All of these can be found here --
Genuine Molex (larger sizes no longer available) --
https://www.greatplainselectronics.com/products.asp?cat=86
Generics (all sizes available) --
https://www.greatplainselectronics.com/products.asp?cat=81

Those 24 pin edge connectors -- had several thousand but now completely sold out for me.
We still do have a few other sizes of Molex edge connectors for Gottliebs --
https://www.greatplainselectronics.com/products.asp?cat=77
And AMP edge connectors --
https://www.greatplainselectronics.com/products.asp?cat=128

I've usually found Great Plains the goto place for connectors.

I think you misunderstood what vid1900 said. .100 and ,156 are 2 different sizes and are not compatible with each other.
Can you post a link to where he said that? You have me very curious now.

.156 male pins don’t fit in .100 holes on the circuit board.

Always repin .100 header & female connectors.
Only if you have the soldering and crimping skills

I have seen a lot of bad crimps when going through games

I just heard about Great Planes Electronics and I spent 6 hours comparing different suppliers but they have the best combination of parts and prices.

I haven't bought from them yet being that I just heard of them about a week or so ago, but I have a couple hundred dollars worth of parts I need to order. I keep refreshing my cart but their store is still closed so I rush ordered parts from Marco for a customer machine so Marco is also a good alternative.

You can also get some Molex 0.156 and 0.100 connectors and pins from Pinball Life.
See attached link for the 0.156 page.
https://www.pinballlife.com/molex-156-idc-connectors-and-parts.html

Which one are you looking for?

It would be nice if a Gottlieb system 1 ,system 80 kit could be offered to replace all of the connectors.

Oh yeah, those 15 and 24 pin 0.062" connectors. I ran out quickly of these two after the last time buy. I found another source for the 15s which were supposed to be identical to Molex connectors and be able to use real Molex contacts. Well... they weren't identical. Now I have two cases of plastic sitting under my Stern Big Game. Useless but too expensive to through away.
Still looking, though.

Regarding Gottlieb System 1 or System 80 connector kits. Doubt that will happen, those obsolete connectors are disappearing fast.