Removed original head unit for new one, now car won't start!

[DBarr]

OK, after browsing hundreds of posts and finally getting the car (1998 D1 V8) to run brilliantly, I decided to change the head unit for a new one.

I disconnected the battery, which I have done many times before, removed the old unit and used an adapter plug made for the D1 and plug in new unit! Quite the easy mission i thought. Connected the battery and presto, new unit works beautifully, sounds great (had not kicked over the engine yet at this point). Turned it off and put back a few bits and pieces and thought i'd take it for a spin and enjoy my weeks of hard work and it would not fire up. It cranked over and over and over but no love! I thought the CPU may have recognised the original head unit was missing.... stranger things have happened... so i plugged in the old head unit. At this point it was basically back to how it was before i even started working on it when the car was running fine. Cranked it over.... nothing... cranked it over again and it just wont fire up.

I ended up putting the new stereo back in and upgrading the speakers, turned it on and the stereo system works awesomely, much better than before but STILL no firing up!

Spent a few hours seeing if this has happened to anyone before. Couldn't find anything.

Checked all the fuses, all good.
Check wiring inside dash, all good.
Thinking it might be the immobiliser screwing with me.

Can anyone shed some light or have i stumbled on a brand new problem that has never happened anyone!? highly doubt it.

[goingbush]

Do V8 D1's have an inertia switch , it might have popped when you were yanking the old radio out ?

If its a chinese head unit connect the wire marked 'brake switch' to ground , and not to the actual handbrake switch , just a thought , I don't think a D1 immobiliser needs the handbrake on to start ??

[alien]

Have you locked and unlocked with the fob to reset the alarm system?

You may want to have read of this and follow the links it contains...
Bypassed the spider - 300tdi (https://www.aulro.com/afvb/discovery-1-a/183276-bypassed-spider-300tdi.html)
I’ve got no working knowledge of the spider but it’s located behind the radio so maybe a wire has been knocked while in there? Worth a look.

[DBarr]

So, its not the wiring behing the head unit, all leads are checked and working as normal with no surprise leads. No wire for hand brake in the area i was working in and there is no spider in my model car. So very strange. Checked the immobilizer and it works fine. I'm at a bit of a loss and might have to bite the bullet and take it in. May just be a coincidence that at that exact time of putting in the new stereo, something else has just let go.