Volvo: Doors lock unexpectedly, volvo 850 wagon, best guess

Question
Hi,

I have a very weird problem with a 1995 Volvo 850 wagon, non-turbo.  Any ideas you could give me would be appreciated.

Sometimes when I crank the car, the doors lock automatically.  I know some cars have this feature but mine does not.  When I'm having the problem, I put the key in the ignition and turn it, the doors lock and the car starts.  However, sometimes when I try to start the car, the doors lock automatically,  the lights on the dash come on, but nothing else happens.  No noise or anything.  Sometimes this happens when the door is open, sometimes when the door is closed.  If I keep trying, the car will start but it will usually go through several tries without starting.

I tried removing and reinserting the fuse that controls the central locking and that fixed the problem for a while.  But now the problem is back and even replacing the fuse did not seem to have any effect.

I know this sounds weird but one time when I was having this problem the key was nowhere near the ignition and I put my foot on the brake and the doors locked automatically.  The car was not running. I believe the door was open at the time.

I have not taken this to a mechanic yet.  I just thought I would run this by you to see if you had any ideas at all so I will be able to speak to the mechanic intelligently.

Thank you!!

Fay

Answer
Fay,
Is there an after market type alarm system on the car that is at fault? I have seen people that have bought used cars that did not know that an alarm system had been installed. If no such system exists check the main wiring harness for chafed wires under the dash far left side.
My best guess would be a malfunction in the after market alarm system.