You need to be careful to not confuse terms and types of communication.

PWM is often referred to as Pulse Width Modulation.

Fords Standard Corporate Protocol (SCP) databus uses PWM methods to send data on the SCP databus.

however, looking at the cougar dash wiring, there is not an SCP databus connection.

The only databus connection line present is the K-line which connects to pin 7 of the obd connector.

You need to find out where else the k-line connects to and find out if its for fault finding only. The only info i can find is that the K-line in fords is used for diagnostics. In earlier vehicles it needed the L-line so that tools could send a "wake up" signal. However later cars do not (such as most 1998 on fords.).

There is nothing i could find that would suggest the dash on cougars use a databus for speed signal.

On the later cars such as focus etc. it clearly is controlled by a databus and you have the databus + and - line for communication.

The cougar should in design terms be in line with early ford digital dashes that used no databus and just converted the electrical direct connections into the output on the dash. The later generation stuff is all databus.

looking at your wiring diagram for the cougar you will see the system code on the wires is "PC" which is the same system code on fiestas, pumas etc with a digidash for speed sensor (as well as other engine sensors and control outputs). You will also note the number 8 at the start which shows it as a sensor signal.

According to that you should have a sensor signal running up that wire to the dash.

I cant find the cougar wiring diagrams for the ECU but i do know that on other similar era cars the datalink pin 7 k-line does not connect to the ECU so if your diagram shows the same then you can rule out databus communication between the ECU and dash.

In that case your wire between ecu and dash should be sending a digital speedo signal for the dash to use.

If you look at the duratec V6 cars you see a direct connection between VSS and the dashboard. As far as i know from looking at dash units from the different cars, they are the same part.

It looks to me that you should be able to send a digital speed signal to the dash and it should work.

The only thing that could fuck it up is if the pulses per mile calculation is for some reason different on the dash compared to the output on the speedo sensor. Ford speedo sensors of the era are 8000 pulses per mile.