1996 Volvo 850 tries to start when I connect the battery cables

[beigg]

Check for exposed/rubbing wires going past the front engine mount and the harness containment bracket. Runs along the horizontal sub-frame lateral support brace.

[Myvolvo850]

It's deffinatly electrical... I decided to just wire I a toggle switch for the time being... works perfect..I'm dreading having to chase down that wire

[BEJinFbk]

I don't think that you have indicated but do you have any aftermarket equipment installed in the car? A bum aftermarket alarm/remote start setup might cause your problem and it will be difficult to sort out. I just wound up yanking one completely out of my son's 850 after it wouldn't start.

One other thing to do is remove the 210/211 relay and see what happens. That will tell you which side of the firewall to focus on. With the relay removed it should not crank with the key and it certainly shouldn't try to start without the key. If it still tries to start with the relay removed then work your way forward through the harness under the hood.

...Lee

A great point about aftermarket systems
and some excellent advice about troubleshooting.

Isolate your problem and conquer that sucker!