Marshall SL5 Clean Channel Issues

[DPM309]

Have a Marshall SL5 that has no sound coming through the clean channel. The OD channel works fine. Traced the problem to the 11-pin wiring harness and connectors (CN23E and 12E) that sends the signal back to the circuit before the tone stack. The cable itself does not have any shorts as I double checked for continuity. Refloated all of the solder connections and the only way to get the clean channel to work is to press down on the blue cables next to CN12. When I release the pressure, it cuts out. Reversed the harness and it worked for awhile. After playing through it for about 5 to 10 minutes, it cut out again. Checked both PCBs for cold solder joints or signs of anything heating up. The OD channel works just fine without cutting out, even when I wiggle the wiring harness. I don't think it is the relay (RL1B) since it seems to be functioning properly. I am running out of ideas. Any suggestions? I have attached the schematic.
Thanks, Dan

[Jon Snell]

Tapping the relay will tell you if it is faulty or not.
I would reflow the connector again and check for damaged tracks on the pcbs. Not much it can be; connector, bad connection on the connectors, damaged feed resistor etc.