Completed wire wrap fixes to replace temporary jumpers,

 WIRE WRAP TO REPLACE TEMPORARY JUMPERS IN 1130

I removed the two temporary jumpers and replaced them each with a permanent wire using wire-wrap onto the backplane pins. This is more reliable and isn't as easy to snag and pull off as the hanging jumpers. If I discover any further issues with failed traces I will apply additional wire connections. 

The backplanes have long square pins sticking out on the backside. Traces on the backplane make connections between some of the pins, but the remainder of the connections are made with wire-wrap in an automated machine. Later in the field, additional connections can be made by the local engineer using wire wrap tools.

The pins have a square cross section. Thin wire (30 gauge) is wound around the pin which creates tight gas-proof connections at each of the 'corners' as the wire bends around. These stay very tight and reliable with no oxidation of the contact area. 

Wire wrap tool and wire

In my experience working with machines from fifty or sixty years ago, wire-wrap links effectively never fail; the rare cases involved wires being snagged and severely pulled. In contract, the printed circuit traces on PCBs and backplanes do fail at a non-zero rate, generally a result of flexing of the board over time. 

My wire-wrapped connection in light blue

Another wire wrapped connection in light blue

COMPLETING CONNECTION OF WIRE LOOMS TO ARDUINO SHIELD, DEBUGGING

I finished wiring up the looms to the Arduino shield, verified the lack of shorts between adjacent solder connections and began testing. I had some problem with the power method I used for the Arduino and need to rethink this a bit. 

Completed attachment of looms to Arduino and shield

I had taken the +12V from the IBM 1130 as an input to a LM7805 regulator to provide +5V for the three relay boards as well as the Arduino, feeding the +5 to the pin marked +5 on the Arduino board. It appears that instead I should feed the +12 to the Vin pin and let the Arduino do its own regulation to +5V. My LM7805 can still power the relay boards.