My heart goes out to you mate.
I understand your situation and heartache.
I recently acquired a Chevrolet Optra similar to yours.
I am the third owner and got the car for peanuts frankly.
But then, it did need a fair bit of work and parts replacement to get it working again.
Anyways, in cases like this where the car is pretty old, I will always recommend getting the spares from the Authorized Service Centers.
In my case, the front disk assembly, the vacuum hose, fan belts and a whole bunch of things had to be replaced to get the car working normally.
The independent garage here in Chennai, that comes highly recommended on Team BHP was of little help as they did not have access to the spares needed to get the car working again.
Ultimately, it was the service center that I had to go to, in order to get the parts replaced. And since then the car has been functioning properly(touchwood
).
I'd recommend you call up the Service Center and speak with them.
It might take them a while to get the wiring harness.
But once they have it, I'm sure it would be much easier for them to take everything apart and put it back together.
Might cost a bomb, but then again, getting an essential part like the wiring harness is an area where I would gladly put my money in.
And my experience with Chevrolet Service Center, here in Chennai atleast, has been good so far.
They listened to my problems. They took a long-ish test drive to find and locate all the issues.
They suggested replacement of all the parts which needed replacement.
And thankfully, after replacing everything they suggested the car has been working really well
. I'm even getting close to 11 kmpl within the city with 100% AC!
Anyways, speak with the authorized service center my friend. I believe that should be your best bet right now.