So you have to be figuring that it's either a fault in the clocks or the loom somewhere.
Probably worth tracing the wiring from the pressure switch up to the clocks and test to see that each wire is intact which should be pretty easy with a cheap multimeter. Then you'll need to check the oil is pumping round, best would be a pressure gauge so you can see a number but you could just measure the resistance at the pressure switch, it'll change as the pressure rises. Just cranking on the starter will do the trick.
If these check out OK then it might be the clocks themselves
