Just about to have a bloody bonfire!!!

[GQPorkroll]

Ok, ignition off, white wire 12v, on 12v. White/red off 0v on 12v

[Yendor]

No I tested the heavy red batt wire, it's zero, and i tested the heavy white wire in the clip and it has 12v. I'm just about to test the white/red wire now with ignition on, it should have 12v shouldn't it?

So the heavy red wire connects to the alternator via the nut? This should have battery voltage.

Originally this wire was white and would connect straight to the battery via a fusible link.

Can you see where this red wire goes to? does it go to that fuse you just found that is blown.

Are you able to post a picture of the wire connections at the back of the alternator and your battery isolator?

[Yendor]

There should be a fuse or fusible link in this red wire. It could be near the battery or near the battery isolator.

Also make sure you haven't left any wires off the battery when you reconnected them.

[GQPorkroll]

Success of sorts.

That wire had been replaced by the previous owner, Rod, it goes to the dual battery system as two identically faded/sized wires run from the dual battery setup. They're in spaghetti tubing, one goes to the alternator, one goes off in a splice of wires, connectors, chewing gum, electrical tape, etc underneath the manifold. Can't see where it terminates.

However I took an alligator wire connector and placed one end on the battery and the other on the middle block of the dual battery system, turned the key on, the battery light comes on. Start the motor, 14.5 on the start side, 12.5 on the aux side.

It works. It's convinced me the dual battery system is shit and the pervious owner was dodger than a seventies car salesman and I will be replacing everything.

Thanks very much for all your help, Rod, it's been amazing. I can assure you that the truck will be fixed properly and I won't need to borrow from your brain again to this extent!!

[Yendor]

No worries at all mate I enjoy the challenge.

I think it's a good idea to get an auto electrician to redo the wiring in the charge circuit and upgrade your isolator at the same time.