Ignition issue, Electrical problem help sought Options

[Bob67]

Help request with electrical problem
I have an intermittent problem with my ignition on my 1972 2.0l which is undergoing a complete restoration. Fuel injection has been replaced with twin carbs

Sometime it starts OK and then next time will fail to start on crank

Turn Ignition on so oil and ign light comes on OK and then when you crank it looses all power ie no starter crank and dials for volts, temp etc all loose complete power light as if something is grounding out the circuit

Fitted and new ignition switch and same issue. The car does start when hot wired using wires directly into black mail connection block without ignition switch

The head lamps, indicators, hazzard all etc work OK but horn , fog lamps and interior light doors switches do not ( although interior light does work OK and the door switch do appear to work properly)