Electrical advice needed

I have a 1982 Yamaha xj750 café racer build that had been working great for the month and a half that I've had it, but I went to the gas station the other day and when I went to leave the ignition refused to show any signs of life on the digital spedo/tachometer.

I have confirmed the battery has a full charge and testing the ignition cable via the connector using a multimeter confirmed that is also working. All my fuses are unbroken and I can't seem to see any clear breaks or problem areas. By switching the key on and off, the display lights up for a millisecond before going dark which I don't understand because it seems to get current for a second and then it disappears. Twice already the electrical problem has "fixed itself" but after reconnecting the gas tank and turning the engine over, the circuit seems to fail again and again.

I am looking into purchasing a new wiring harness but I am not entirely sure that is the issue. Any experience would be greatly appreciated.

 

Id start of by making a cut on each side of the main fuse and seeing if its 12v on both sides. Replace all fuses even if they look good. Lmk

 

If you still have the old glass type fuses in the bike you should change them over. That is one of the weak spots of the electrical system for most of our older bikes. Even is the old fuses look good often they are not, or have bad contact to those old brass holders.

 

sounds more like the ignition switch itself ,or the connector block that it plugs into, you can find the connector , unplug it and bypass the switch by bridging out the two main wires. not familiar with the 750 but wire colors are usually red and brown.
that wont cost you nowt, if the switch proves to be the culprit, it can be stripped and cleaned, still costing you nowt.
stu

 

Check the connector from the right control at the main harness it may not be tight but the pins maybe boost in their connection internally