Simple electrical issue! Need a hand pinpointing it

[bufter]

Hi all! Figured this is a better place for an electrical issue than the derv page.

My car randomly wouldn't turn over on the key xmas day. Now when i put ignition on, I get the stop light on on the dash with the battery light, and the headlighta are flashing on and off for a few seconds..alarm?)Glow plug lights up as normal and goes out. 

Try to start the car and theres nothing. Interior lights dim but theres no 12v feed to the starter solenoid. Car will start and run if you cross the starter connections with a screwdriver. Also the radio will come on and flick off, and do this continually. For a while it would stay on if volume was low and go off when you turned it up.

Now every time.I turn on the igniton or open the car door the flasher unit goes off???

Someone help before I put a match to this POS

Thanks

[bashbarnard]

Check the big plugs on the chassis leg

[Eeyore]

I was going to say battery until you said it will start if you short it. Is there a relay for the starter?

[bufter]

Had both plugs off, neither have corrosion in but sprayed the points and put them back together. This wouldn't affect starter motor circuit though would it? 

As as to whether there's a starter motor relay, there are two relays in the wiring behind the battery, they seem to click randomly when engine is running and when it's shut off and ignition on..I also see a small black electrical unit behind the battery which could possibly the +ve control unit or something in the haynes manual? Bypassed that and still no change.

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The problem briefly disappeared today, however when I washed the car this afternoon it was back with a vengeance.

[cully]

check the large lead connection on the alternator there should be two leads One large one smaller on the largest connector and just one small on the other

sounds like the main terminal is burned up on the alternator

[bufter]

The terminal on the cable itself is solid..could it be knackered inside? And would that cause the radio issue too?

[bufter]

Took to an auto electrician today and they pinpointed the problem to be the immobiliser. So it was bypassed and disconnected and my car is good as new again