hi all!

I have a big big problem on my 2wd sierra

originally my car were a 1.8 ohc carburettor, now it is 2wd cosworth

but now won't start.... i have the fuel from pump, everything can be in good condition but at the moment i have no spark at plugs... the coil is brand new also the rotor and distributor cap, the plug wires works well and tonight i noticed the prblem:

i have the current from the coil to the distributor just for a while the ignition is switched on or off but when i try to crank the engine i have no spark...
i cecked everything... ignition amplifier, map sensor, iscv valve, fuel pump, injector and so on.... i think the problem can come from the crank sensor or from the sensor in the distributor.... (i don't know how to ceck them)

any help?
is there any possibility that i done a wrong connection of the loom under the steering column?

please help me... i really don't know how to solve this problem

thanks in advance from Italy