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)

[Bob67]

Many thanks for comment
I have installed new gearbox earth strap and battery earth cable, would you still recommend adding another then to the engine? Doesn't the gearbox earth have the same function?
Starter motor, battery, coil, leads, distributor etc are all brand new. I did remove paint and clean all body earth points but will do so again to be sure

We cant seem to isolate why the fault is intermittent and has no issue cranking when hot wiring it. This would suggest it isnt and ground issue at the earth points but perhaps it is grounding out somewhere else on the loom perhaps???

[brcacti]

Many thanks for comment
I have installed new gearbox earth strap and battery earth cable, would you still recommend adding another then to the engine? Doesn't the gearbox earth have the same function?
Starter motor, battery, coil, leads, distributor etc are all brand new. I did remove paint and clean all body earth points but will do so again to be sure

We cant seem to isolate why the fault is intermittent and has no issue cranking when hot wiring it. This would suggest it isnt and ground issue at the earth points but perhaps it is grounding out somewhere else on the loom perhaps???

I seem to have the same issue, a year ago I went through SO MANY ground and contacts, cleaned and sanded to work for one year then come back as before.