What sensors would send a signal to the computer, NOT allowing the car to start?

[police interceptor]

I know there are a bezillion sensors in a 98 Crown Vic. What sensors would send a signal, limiting the ability of the car to start?

Are there any sensors that would send a signal limiting the operation of the electric radiator cooling fan from coming on and running (it runs when you first start the car, or jump wires)?

The mechanic is stating that electricity is not going to these devices (2 separate cars), in one the fan is not coming on, when it does it comes on high, stays on and burns up wires, the other the starter will not engage as it is not receiving a signal to engage. The mechanic is now statting that both cars have a wiring harness problem and is about to pull out the siring harnesses. Any suggestions?

[SCPDMechanic]

I have a few Crown Vics in the fleet that had problems with the main eng harness rubbing and chaffing. Usually under the front bumper right where the bumper support ends. Peel away the conduit covering this part of the harness on both sides (DONT USE A RAZOR KNIFE UNLESS YOUR A SKILLED TECH!) and check for rubbing wires. I've had to repair many of these...... sometimes 8 wires at a time.

As for the fan motor problem, check the fan motor relay. Make sure the contacts aren't stuck together causing the fan to stay on. There is alot of amperage going through that thing and its a very common problem with Crown Vics.

[radioman2002]

I would also check a big problem that is real simple to fix, check the fuel cutoff control in the trunk. I was on a Fire Investigation one time, threw my equipment in the trunk, went to start the car and no start. Luckily I realized that I might have hit the cutoff switch, by accident. Just reset it and was on my way.