security problems with my 1991 fleetwood

I have a 1991 Fleetwood that is rust free, looks great and runs like a new car. My problem is when I put the key in the ignition ,if the security light comes on the car will not start. If I wait exactly four minutes and try again it usually starts, but not always. Some times I have to go through this procedure three or four times before it starts. Any information would be greatly appreciated. Thank you!