heater controls.Heated rear screen/radio circuit

Hello, me again with 92 BMW E36 318IS,which is now running very well since I decreased the Thermostat opening temp from 92-94 deg too 82-84 deg, the  TOP of The engine is now getting coolant on short journeys along with a change of Petrol Pump it is running well, I still have yet to change the Fuel Lines that became very SOFT BECAUSE OF THE HEAT on the top end. If you have similar issues, YOU CAN TAKE THE THERMOSTAT OUT ALL TOGETHER until you get one. Fuel Pump change over for a submersible was nice because it was inside the car under the back seat behind the Driver, you were not crawling around underneath.
I am now working on a couple of small issues; 1) what actually controls the Heater, I know you turn the knob; Is it the switch mechansim  or what, the Fan works and the heater works but only on HIGH SPEED.
2) Why did BMW include the Heated rear windscreen on the same circuit as the Radio Circuit, I switch on the radio, and rear screen heater, at the same time and The radio gets interferrence, other than seperating them or installing another supressor, IS THERE A SIMPLE FIX.
anyone out there let me know.
a couple of Local BM heads one a BMW Mechanic was astounded how the Flat Spot was corrected, not just me, a friend in the States sent me about 10 pages about Flat Spots, and being a typical Scotsman, I started with the cheapest parts and that was thermostat, I even made the gasket out of Leather, and then used my straight 6 fuel Pump out of the Jeep I just Broke and sent to the breaker.
Let you guys and gals know, I am now aware of the Back Suspension Springs are prone to breaking and with the Roads as they are, there is a really good YOUTUBE Video by a German showing how to change them in around 10-15 minutes, with no special equipment or taking all the parts off that BMW SAY YOU HAVE TOO. I am also looking into what Heavy duty stiff springs are available that will fit, or if anyone knows of good stiff rear springs already let me know.
By the way; although the car is growing on me and my dog, I really do need a 4x4, older the better, as I spend most of my time in the North of Scotland and Winters can be harsh, I would take a straight swap not discovery's or range rovers, or any of the modern Plastic City 4x4, old 90 or 110, or even another Jeep Cherokee, or a Jeep CJ, I may still keep the BMW, as it qualifies for Modern Classic Insurance, and is very cheap to run, comfortably 45-50mpg at 55-65 mph, and goes like stink when you need it too.
JimmyBrown