Weird issue seems to be cropping up. Stereo has been in the car for at least 7 years.

When driving, and I hit the brakes, the stereo goes off, then comes back on.

It's gotten to the point where I can make it happen consistently.

I suck at electrical. Where should I start looking first?

TIA

Two things:

Check/clean grounds

Make sure your alternator is fully charging. 13.5V+ when running.

LOL when I worked for a cellular company we used to wire up a pezio to the brake light with a relay so when the sales reps would pick up thier cars they would freak out as they drove away!!

Sorry your story brought back memories!

Make sure your brake power wire under the foot board is not coming loose and touching ground.

Where in LA are you? I am in Hollywood until 2:30 tomorrow, if you are close I can take a look for you!

There is a bundle of wires under the pedal board. I suspect the brake pedal is chafing against some wires as you stomp on the pedal.

could be as simple as a loose connection joe. im not sure but i dont think the stereo wire run in the loom behind the pedal board. start at the back of the stereo and follow the wires and wiggle them as you follow them to their connections. is it a later aftermarket stereo?

Also check the fuses. Weird stuff can happen when one pops, or even when the contacts (the "fingers" that hold the fuses) get dirty or corroded.

--DD

dave, do you recall what else is on that circuit?

Also is doing it when I hit my directionals, but not a consistently.

Shouldn't the brake signal switch be on the master cylinder? I'd get to that under the car, no?

That's just the low fluid switch. They're talking about the brake light switch, which is down by the base of the pedal cluster. There is also a bundle of wires down there that runs through that area which you should check for chafing.

This may sound odd but those are the exact symptoms my car had when i forgot to reconnect the alternator after having the motor out (i was really rushed to get it back together) my battery voltage slowly dropped and first it was the brakes causing the radio to turn off, then the turn signals, finally it got so that the brakes would cause the ignition and the radio to shut off....i ended up on the side of the road and had to get a jump

Funnily enough, I threw the alt belt about a month ago. I better check everything out under there.

No. It is on the pedal cluster.

This doesn't help, but it sounds like you have actually acquired a new feature. I am not sure how one would pitch it, but it would allow conversation at stop lights and also your booming base would not distract the cars within two blocks. Good luck, sounds like you have some help already.

There are two switches. One, which controls the brake lights at the back of the car, is on the pedal cluster.

The other, which controls the brake warning light in the combo gauge, is on the master cylinder itself.

I believe the former is the one you'd be interested in for this problem, not the latter--as was stated already. But it's not hard to get them confused when you're just talking about them.

--DD

I got my noggin down in there this morning, and pulled the switch. I believe it works, but I think there may be a grounding issue.

When I removed the switch from the cluster, radio doesn't shut off when I hit the brakes, so it is related to this switch.

There is a post on the switch. I've looked online, but there doesn't seem to be a use for that post. Is it for a ground? Should I run a separate ground to that post?

I will clean up the wires and stuff under there, and make sure it's all clean.

Any other ideas/suggestions?

TIA

Cleaner everything up. All of the connections. Nothing impinging or otherwise inferring.

What next?

To help narrow down if it's a ground or a hot wire problem, follow these steps:

I would run 2 sets of TEMPORARY jumper wires (1 positive/1 ground) from your stereo to your battery elliminating/disconnecting what is feeding your stereo. THis is to bypass the car wiring.

From there, I would connect an idiot light to each source;
First from the original stereo ground source to a positive source. Turn on radio, press on the brake pedal see if idiot light goes away. If it does, then you definetly have a bad ground. If NOT, then possibility it's the possitive side, proceed to next step.
Same step as before, however connect the idiot light to the original stereo positive source then to a ground. Turn on radio, press on the brake pedal see if idiot light goes away. If it does, then you definetly have a bad POSITIVE source to the stereo.
If NOT, then alternator or bad car ground issues.

That will let you know whether you have a ground issue, or a possitive issue.

Hope this makes sense.

I had the same issue with my first 914, the PO had the aftermarket radio wired to the voltage gauge on the center console so every time the brake lights were engaged the radio would cut out.

This stereo has been in there for years. Why now?

So weird.

You said this happens "when driving". Is it happening while the car is stopped?
You may have a loose power or ground that is swinging with momentum as you decelerate and loosing contact. Then is comes back to rest and reconnects.

I've seen it happen.

Happens when the car is stopped and not moving.

Its something in either with switch or wiring. Will be check tomorrow (assuming I can find some time).

Does it happen as soon as you touch the pedal or after a bit of travel?

Trying to see if it's the brake light switch or a physical interference.

Can you activate the brake switch by hand and see if that causes it?

Been busy the last few weeks.

Going to be looking at this again this week.

In addition to the light testing method list above, I plan to check all of my grounds. Here's my list of grounds:

Battery
Trans
Relay Board
One under dash from stereo

I've checked and cleaned my fuse block.

As mentioned before, I get the same issues with the directionals.

Any other hints or suggestions? Please let me know.

Thanks!

clean fuses and contacts
clean chassis ground point stud to left of fuse panel

clean chassis ground stud on wall to left of relay board in eng comp

Finally had some time Sunday to take a good look.

Cleaned the grounds, particularly the one directly from the radio.

MUCH better. It still happened once this morning on the way to work, but that's it.

Thanks all for your help!

I too believe this is a voltage issue. I had the same type of problem in my 928 when the voltage regulator was going out. It was fairly intermittent at times too. Mine would shut off the radio because it is the most voltage sensitive item on our low tech cars. I found it only happened when the car was down to idle, is yours doing this also? If I came to a stop and kept the revs up a bit (keeping the alternator charging) it would never shut off. It was most prevalent when driving in the rain because the wipers were using even more voltage.

Do you have an MSD in the car?
if so...I bet you is hooked up to one of the wires feeding the MSD...

Hi! Is this problem still happening? I just got a 914 ('74 1.8) and am having a similar issue with the turn signal turning off the radio. The radio is after market.

Thanks