Yes, and pinball machines tend to act very strangely when there is a short. When something doesn't work I found it is very easy to fall into the trap of over reacting! I was checking connections between the opto board and the optos, the opto board and the power and CPU boards, checking for continuity, etc. I thought about just buying a new opto board, even cutting wires to isolate the problem! And all the while I was focusing my attention in the wrong place. (To exacerbate the problem, by coincidence, i had some other unrelated problems going on with the machine, some related to the problem and some not..and it started to overwhelm me) Luckily I've been doing this a long time and have learned to ask for ideas, as I did here, and to stop and think!
Whenever I think about taking some drastic action, I walk away from it a while and think. Think about all the facts. After all, in this case it worked before in the recent past. I had just done a bunch of fiddling around with the machine (in other words, making a lot of changes at once) and didn't connect the outage with the installation of the LEDs.
In the end I got out the manual and checked the schematics with relation to the opto that was failing. I then opened the machine and started tracing every wire in the same matrix. It was relatively easy, took a while, but I did it methodically and calmly, not knowing what I would find. That's when I saw the light metal tab touching the metal part of a diode on a switch. I simply turned the fixture so it wasn't touching, and everything went back to normal!
I share this with you all in the hopes it may help you in the future. Good luck and keep flipping!