S plus , coins drop straight to tray , No candle lights ... suggestions please

[ZZPOPZ]

As title states , when I put a coin in my s plus the coin drops straight to the tray. Candle lights are no longer an issue as I know the problem.

This is the s plus with the MPU on the back wall, the bill validator and cash box were removed prior to me getting this machine. I bought it as a non working slot and have since got it working but I have no way to put credits on the machine other than using the white button on the coin optics.
Things I've done ... not necessarily in this order
1. swapped both the MPU and motherboards with known good boards from another working machine. no change so put the originals back in.
2. did a ram clear on original board because stuck in code 61 and then 61_1 loop
3. checked all fuses on power supply.. all good
4. checked continuity on the harness that plugs into left side of coin comparator . all wires good
5. swapped out that harness with one from a working machine.. no change .coins still drop thru
6. I did the pot adjustment to change comparator sensitivity as well as changed the sample coin, no change
7. I took a coin comparator from a working machine and installed it in this one ..comparator didn't work ,coin still dropped thru.
8. took the original "non working comparator" and installed in working machine and it worked as it should. So believe that comparator is good
9. also slot machine main door optics have a broken wire so I made a bypass jumper that I plug and unplug to simulate opening and closing the door.. purchased a set on ebay, awaiting delivery.
10.I don't see any light from the coin optics board, however the add test credit button works  to add credits. Currently my only way to add credits and play.
11. checked wiring harness and no visible breaks.
12. checked the molex connector on mother board for burn marks, looks new. disconnected and reconnected and wiggled it . 
13. checked voltage on yellow and black wire to side on coin comparator. 24 volts present. this was checked at harness connection one back from the comparator as my probes couldn't fit in the connector at the CC.
The candle is unplugged because its connector doesn't match the one on the harness.. related ?? I doubt it, but I'm no expert on these machines.
Again the machine will play when I add credits from the coin optics test button , I had a couple of nice hits and have a couple of hundred credits and it plays those normal.
Sounds work.
Insert coin light comes on the front display
Would a bad coin optics board cause the CC to not work?
If anyone can point me in a direction to check it would be greatly appreciated .
Loose connection ? bad or missing ground ? Fuse I cant find ?  tests I can try ?
Thanks in advance.

[Badbaud]

make sure the Vb 8 volt fuse is still good.

[ZZPOPZ]

Thanks for your quick response.  If you are referring to the  middle fuse on the power supply ,yes the fuse is good, checked continuity with a meter. All three of the power supply fuses are good.

Also I will edit my original post , I found the reason for the candle lights  not turning on....... wrong candle , the connector on the candle doesn't match the connector on the harness so it is unplugged.

[ZZPOPZ]

"...no visible cut wires..."

You can't see underneath the wire covering.
Use a multimeter and check from both ends of the shorter coin comparitor harness.
You can disconnect it from the main door harness.

Check the black ground wire for continuity...that's usually the problem.

Stayoutathebunker.... It appears that you edited my original post instead of replying to it...... No worries ,i will repost my issue.
  I did check it for continuity and it was good. I also swapped in the harness from another machine  and no difference.
Good point though, I will check other wires for continuity, a bad ground would make sense.

[ZZPOPZ]

Another observation.
From what i've been reading here the LED on the CC only comes on when the door is closed, with my extra long jumper wire set up to bypass my broken door optics the machine has been tricked into believing that the door is closed even when open unless I unplug my jumpers. Well with the door in the "closed" position the LED remains off. I don't know what this means but it is contrary to what i've read.

Thoughts?

[jay]

Per your post:
"Insert coin light comes on the front display"

This is important because it means it sees your door as closed.
From your description it sounds like all the parts have been tested good but the coin in is not working.

I would be following the harness's back to where they are plugged in. It sounds like the components are not getting power.