There was a acknowledged safety design shortfall, with all Williams System 3-7 pinballs.
There is no fuse on the AC supply side to the 2 backbox mounted bridge rectifiers. (bridges convert AC current to DC current)
Bridge Rectifiers can fail, or short, depending on the type of failure, you can end up with the AC supply line becoming so hot, that the coating, or what ever it’s touching flames.
I have seen the after effects of this scenario twice in my lifetime, and in both cases, no fire, but lots of smoke, and a really bad smell; plus having to totally replace some wiring from the transformer.
The images in the Photo Gallery should help you install this, if you have questions call me at 306-955-6636.
The 2 bridge rectifiers each have 4 lugs, with wires attached.
Note, in the photos that one has a “+” sign, and one has a “-” sign beside them, these are your DC outputs, we DON’T want to work with them.
The other two (unmarked) are the AC inputs from the transformer.
Do one bridge at a time, pinball is now UNPLUGGED from the wall outlet.
Pick one of the AC inputs, it does not matter which one, snip the line about 4 inches back, strip about 1/2″ of the insulation, and brazen it with soldier, just like the ones that arrived with this kit.
Use the line coming from the lower cabinet first, and soldier it to the lower line on the fuse block. (At this point I’m assuming you have mounted the fuse block, as pictured)
Now, slip a piece of shrink tubing onto the line, and seam them together with your iron, once done, slide the shrink tubing over the seam, and heat the tubing to shrink and cover the seam.
Now, repeat this procedure with the same color of wire, from the top of the fuse block to the snipped line attached to the Bridge Rectifier.
Then repeat this process for the other bridge rectifier, and your upgrade is complete.
Be aware that the photos attached show stock bridge rectifiers from the Williams factory. If both, or one of yours looks different, and you cannot see any indicator markings, STOP, do not proceed, until you send me photos, and we sort out exactly what lines you need to tap into.