[TWJ]

Need a little help from any electrical engineers out there...

I just installed a period Blaupunkt radio in my '72 T after removing a 90's Blaupunkt. The period radio works great when the car is not running but with the key turned on, however when the engine is running it makes a very loud hum almost drowning out the music. Why would this be??? Grounded incorrectly? But why does it hum only when the engine is running?

When I installed it I connected the ground to a wire that connects with many other wires then to a ground. This is the same ground that the newer radio had used. I connected the positive lead to a yellow wire with an inline fuse that is controlled by the ignition switch. This to was used by the newer radio although it also had a positive lead that went directly to the battery.

How do I stop it from humming?

Why did the newer radio, using the same wires, not hum???

Any help would be greatly appreciated!