Small but nagging problemsm

[PistolGrip]

I’ve had my mostly bone stock 1994 Mustang Cobra 5.0 for 20+ years. For the past few years the stock radio has had a distinct buzz that is clearly the engine firing. This only happens when the engine is running. The higher the engine revs, the greater the interference. I,ve been all over in the engine compartment checking for bad grounds, and have found nothing wrong. I recently pulled the radio out and noticed an off-white little box….the size of a small matchbox that has a red wire and black wire going into it and the same colored wires coming out the other side. I don’t know what it does, but wondering if it could be the culprit. To make matters worse - this interference problem comes and goes in no predictable pattern and is NEVER a problem when the engine isn’t running.
My other problem is the dash mounted clock has died. It’s getting power The part # is F4MF 15000 AB.
Any help on either of these would be appreciated.
If I’m slow to reply, please be patient - my computer broke, too!
Despite these hurdles, life is still good!
Thanks, Mark

 

[RAU03MACH]

Ttocs would probably have that answer

 

[Rtfm]

Do you have the original Motorcraft distributor? I had an aftermarket distributor cause such interference.

 

[ttocs]

pop the hood and look at the coil and there should be a small metal cap/can with a single wire going to it. It is an ignition noise reducer and for the life of me I can't seem to find a link to show it. cj's use to carry it

 

[95opal]

Is the stock capacitor by the coil still hooked up?
If not could be your problem.
Ford part number 7L1Z-18801-A
Make sure your speaker wires are not near any power wires.

 

[PistolGrip]

Do you have the original Motorcraft distributor? I had an aftermarket distributor cause such interference.

Yes, original distributor.

 

[PistolGrip]

Is the stock capacitor by the coil still hooked up?
If not could be your problem.
Ford part number 7L1Z-18801-A
Make sure your speaker wires are not near any power wires.

I’ll check the capacitor. Speaker wires in original location. They’ve never been messed with.

 

[Wood's 5.0]

All good information above. I bought my '95 new in late '95 and it developed a hum/buzz that correlated with engine RPM not too long after. That's been so long ago now. I want to say there was a TSB associated with it but my memory is the second shortest thing I have these days. I remember changing the wiring harness was what was called for but I wasn't interested in that as it seemed to involved. The tech added a ground from the factory harness that plugged into the radio and that fixed the problem.

 

[PistolGrip]

I’ve ordered a new capacitor (around $20)
Hopefully that will do the trick. Thanks to all!