Damaged a lead whilst replacing fan belt

Hi,
I wondered if i could ask for some help.
Tonight i was completing the replacement of a crank pulley. I decided to replace my belts whilst i had the radiator off. I'm kicking myself now, but i have broken off the plug part of a lead that goes into the engine block whilst trying to tighten my alternator belt with a pinch bar. I must have just caught it and the plug was very corroded and brittle. I hadn't noticed it was damaged until I took it out for a spin around the block and after 100m's everything died and I've had to abandon it on the pavement at the end of my street! The immobiliser light came on when the engine turned off.
The plug is in a tight little spot behind the alternator and the flex comes up and joins onto another loom heading back towards what I presume is the main loom.
Any advise on the cable name and its function would be much appreciated

I should have said its a 52 plate 16v m13A engine

Sounds like the crankshaft sensor

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Thanks for that. ill try and get a photo tomorrow in the daylight. it looks like the male plug is also damaged so i might need to replace that also.

just taken a look at the damaged sensor. I would say it is a cam shaft sensor after seeing one online. my other issue is the plug part is knackered also. would i need a replacement lead complete or can I refit a new male plug by re crimping the wiring ?
Thanks in advance.

Camshaft sensor is normally located at the rear of the engine at the top

They look very similar

www.bigjimny.com/store/crankshaft-sensor-p138.html

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This is the lead it isn't to the rear of the engine but in a tight spot to the side of the alternator. i can't get my phone in the there to show the position of the plug into the block its so tight