Hello, I have a 66 chevelle ss with power brakes. I installed a custom auto sound radio and everytime I press brake pedal there is a pop noise thru the radio speakers. Also installed mallory e-spark ignition and since then whenever I turn off the car with radio on an even louder pop noise goes thru radio. I did put a new capasitor on the back of the coil connected to the positive terminal of coil but that didn't fix it. By the way I upgraded my coil to a pertronix flame thrower. I was getting the pop with brake application with the old points and factory coil but not the pop when I shut the car off. Any ideas to fix this would be greatly appreciated. Thanks, Wayne

I am not a radio expert, but there are others here that are. How is the radio wired? Where are you getting power from? Where is it grounded? What kind of charging system (external, which is original or internal) ? What is the voltage at the battery with the car running at a fast idle? Do you have all the ground straps on the engine?

Maybe getting one of those small electrical filters to stick inline in the radio will help. The old cars had a lot of things that introduced interference into the radio, but why it pops when braking is beyond me. Maybe theres a not-so-great ground somewhere, and the flex of the chassis under braking is affecting it?

it sounds like you need to change where you're pulling the power from... install filter in power line & change were your grounding the radio !! you didn't put the ground wire into the harness did you ??

I have my power coming from the fuse panel accessories male plug. The radio from custom auto sound has a filter built into it and the fuse that is in the filter box is ok. I have the groud connected to a bracket on the steering column that has a wire harness plugged into it and a relay next to it which everything is fastened to the steering column. I think it is the chassis wiring harness but I'm not sure. Sorry I don't know what the ralay is for. It is close to the brake light switch. Could I be picking up interference from that switch when I apply brake pedal? All my ground straps are attached and I think in the correct locations as per diagrahms. Thanks, Wayne

I wonder if it's from the brake switch contacts arcing ?. Below is some info:


With both AC and DC, contact arcing can be minimized with the addition of a "snubber" circuit (a capacitor and resistor wired in series) in parallel with the contact, like this:

http://sub.allaboutcircuits.com/images/04015.png

A sudden rise in voltage across the switch contact caused by the contact opening will be tempered by the capacitor's charging action (the capacitor opposing the increase in voltage by drawing current). The resistor limits the amount of current that the capacitor will discharge through the contact when it closes again. If the resistor were not there, the capacitor might actually make the arcing during contact closure worse than the arcing during contact opening without a capacitor! While this addition to the circuit helps mitigate contact arcing, it is not without disadvantage: a prime consideration is the possibility of a failed (shorted) capacitor/resistor combination providing a path for electrons to flow through the circuit at all times, even when the contact is open and current is not desired. The risk of this failure, and the severity of the resulting consequences must be considered against the increased contact wear (and inevitable contact failure) without the snubber circuit.

The use of snubbers in DC switch circuits is nothing new: automobile manufacturers have been doing this for years on engine ignition systems, minimizing the arcing across the switch contact "points" in the distributor with a small capacitor called a condenser. As any mechanic can tell you, the service life of the distributor's "points" is directly related to how well the condenser is functioning.

Here's where the above info came from:

http://www.allaboutcircuits.com/vol_4/chpt_4/2.html

Jim
http://www.allaboutcircuits.com/vol_4/chpt_4/2.html

Holy cow Jim, no wonder I hate electrical problems. The solutions are just as confusing as the problem itself. Thanks for the info you sent. If I understand even a little bit of all that its' that my ground wire might be too close to brake light switch. So, this weekend I will move my radio ground wire to somewhere else on the dash and see if that helps. Still not sure why it's popping when I turn off car. So if anyone has any suggestions would be glad to hear them. Just maybe the wiring gods will be looking down on me and solve both problems when I move that ground wire. Did I mention I hate electrical problems...... Thanks Wayne