AM Radio noise

[BackInA88]

I get a lot of AM radio noise but when I apply the brakes the nosie goes away.
I have checked all the grounds I could find under the hood.
Are there ground lugs under the dash I can check?
Or better yet has anyone else had this problem and found a fix?

Steve

 

[KevLar]

Does the noise go away when you apply the brakes standing still or only when the vehicle is moving ? I was thinking that the two would possibly indicate a different cause. If the noise stops when you hit the brakes and the truck is stopped, then I would suspect a short or other sort of contact related to the brake pedal assembly. On the other hand, if it only happens when the truck is moving, then perhaps the deceleration of the truck is causing some loose wires somewhere to contact something they shouldn't...
That's the first thing I'd check, to at least narrow down the potential source of the problem.
Kev

 

[BackInA88]

The noise gets a lot less when the truck is moving or not.
I can just lightly touch the brakes with my left foot while cruising down the road and the radio sounds much better.

Steve

 

[KevLar]

OK so a light touch of the brakes when the truck is moving or not doesn't support the theory of deceleration and loose wires... Without actually hearing the radio and how it changes from bad to good it's hard to point you at a potential cause. However, does the problem "sound" like something resulting from reception (e.g.: antenna), or more like a short ? In other words, could it have something to do with the antenna, the cable or the connection from the antenna to the radio ? Depending on the effect on the radio, you would be looking at 2 different types of problems. Is it a factory radio or aftermarket ? If it's aftermarket, maybe the installer was not careful in how he ran the wires and left them loose enough that there has been some chaffing... Probably the easiest thing to do would be to carefully look at the brake pedal and associated linkages to see if there are obvious signs of wires for the radio or the antenna cable itself that have chaffed and are shorting to some part of the brake pedal linkage. When you hit the brakes, the (metal) part making contact moves and the short is eliminated....
Kev

 

[BackInA88]

Factory radio.
Sounds great when you touch the brake pedal.
So I think the antenna is good.
I think it is a ground issue as I can hear what sounds like both the alternator and blower whine when I am not touching the brakes.
I as hoping some else had gone down this road and found a ground connection I have not seen to point me to.

So truck off, radio sounds fine.
Truck on, if I touch the brake it sounds fine.
Truck on, no brake, blower and alternator whine.

I think I'm ground the radio better thru the brake circuit when they are applied.
I'll pull my lights out this weekend and check for ground connections in there.

 

[KevLar]

Yup, based on that latest intel, I would say it sounds like a ground problem. I had a bad ground after replacing the stock radio in my '96 Disco and it took a while before I found the problem was a bad solder I had made. The threads I read here relating to that are not very specific as far as location, unfortunately it's a hit and miss process. But you do know that it has something to so with the brakes, so that's useful. You could try removing the fuses for the braking system (rather than the lights...) and see if that makes any difference... I think there are fuses in the fuse box as well as under the hood if I'm not mistaken. Intuitively I would be more suspicious of the linkage of the brake pedal assembly than some kind of brake system electrical short to the radio circuit... There are plenty of wires behind the dash that could run close to the brake pedal linkage which is also on the inner firewall, but that's just intuition...
Kev