Not a complete list, I was still figuring out the ones that lead into logic:


TOP LEFT OF BOARD VIEWED FROM FRONT:

------------------------------------------
|
| [======1=====A]
|
|
| [======2=====A] [======3=====A]
|
|
|
|

1A = parity high LED
1B = parity low LED
1C
1D
1E
1F
1H
1J
1K
1L
1M
1N
1P
1R
1S
1T
1U
1V
1W
1X = data LED 0
1Y = data LED 1
1Z = data LED 2
1AA = data LED 3
1BB = data LED 4
1CC = data LED 5
1DD = data LED 6
1EE = data LED 7
1FF = data LED 8
1HH = data LED 9
1JJ = data LED 10
1KK = data LED 11
1LL = data LED 12
1MM = data LED 13
1NN = data LED 14
1PP = data LED 15
1RR
1SS = 
1TT =
1UU
1VV

2A = ADRS ERR LED
2B = PAR ERR LED
2C = address 9 LED
2D = MASTER LED
2E = address 8 LED
2F = PAUSE LED
2H = address 7 LED
2J = RUN LED
2K = address 11 LED
2L = address 17 LED
2M = address 10 LED
2N = address 16 LED
2P = address 6 LED
2R = address 12 LED
2S = address 3 LED
2T = address 13 LED
2U = address 2 LED
2V = address 14 LED
2W = address 1 LED
2X = address 15 LED
2Y = address 5 LED
2Z = address 18 LED
2AA = DATA LED + strangeness on right hand side
2BB = address 19 LED
2CC = address 4 LED
2DD = address 20 LED + DATA LED + right hand side tracks switches when low
2EE = address 0 LED
2FF = address 21 LED
2HH = DATA LED + strangeness on right hand side
2JJ = DATA LED + right hand side tracks switches when low
2KK = address 20 LED + DATA LED + right hand side tracks switches when low
2LL = DATA LED + strangeness on right hand side
2MM = DATA LED + right hand side tracks switches when low
2NN = DATA LED + right hand side tracks switches when low
2PP = DATA LED + strangeness on right hand side
2RR = no effect
2SS = DATA LED + strangeness on right hand side
2TT = 
2UU
2VV

3A = out 0
3B = out 1
3C = out 2
3D = out 3
3E = out 4
3F = out 5
3H = out 6
3J = out 7
3K = out 8
3L = out 9
3M = out 10
3N = out 11
3P = out 12
3R = out 13
3S = out 14
3T = out 15
3U = out 16
3V = out 17
3W = out 18
3X = out 19
3Y = out 20
3Z = out 21
3AA
3BB
3CC
3DD
3EE
3FF
3HH
3JJ
3KK
3LL
3MM
3NN
3PP
3RR = out 5v
3SS
3TT
3UU
3VV = out 0v