Hi, I have been having a problem with my 84' F150 for a while now. It has an after market Sony headunit with 10-disc changer behind the seat.
When I first put my KC off road lights on, I noticed that whenever at a low RPM, if I tried to have the regular headlights and the KCs on at the same time, whenever I would tap the brakes, my headunit would cut off then turn back on. So I figured it was the alternator since the headlights would flicker even just with nothing else running.
So I put in a 140AMP Powermaster alternator with internal voltage regulator, disconnected the old regulator too.
Problem seems to only have gotten worse... a lot worse.

Some times it won't do it much at all, but other days it will do it constantly when some of the following things happen:

When I hit the brakes (even if I am still holding the brake in, it will come back on for that period until I let off and hit them again- in which it cuts off and turns back on again).
When I either pull on my headlights or flick on the KC's.
When I am accelerating, then let off the pedal. Or accelerating and the transmission up shifts.
When I put on the turn signals (sometimes the radio will pulse on and off with each 'click' sound of the turn signal).

I know the headunit itself is turning off and on because I can watch the led's in it go off and then back on when its doing it.

I am fairly sure my alternator belt keeps loosening (think the pulley on the new alt. is slightly smaller then the previous), and probably could use a replacement anyhow.
Could it a loose alternator belt screwing with me since mostly when it does it, there is a drop in RPMs, so a drop in amperage the alternator is making, so a loose slipping belt would be making even less?

I've heard to check my grounds and connections... but I don't even know where to start with that. It gets extremely annoying so I would really like to remedy the problem though.
Also, I am going to try and get a new V-belt that is a little bit shorter in length to make up for possible smaller pulley (when tightened as much as I can get it, it looks to be almost at the end of the adjuster's tightening limit).

Thanks!!!!!!!!!!! Open to any ideas or input!!!!!!

 

Ok. Sounds like you are experiencing voltage conditions less than the CD players operating voltage when the lights are on. Then you went and "upgraded" the alternator now the problem is worse.

This is what is going on. Before the lights you werent drawing too much power. Now that you have added the KC's they need a lot of current and pulls down the available power in the car prolly below 9-10V. THIS IS BAD!! It can damage circuits in the car. Therefore your CD player shuts off to save itself.
Now the "upgraded" HO Alternators at idle/low RPMs actually produce less power than the OEM's. This is because the "tuned" for high RPM loads. Goes back to Mobile SPL competions. They need the most possible power and high RPMs are where thats found. Also it looks good on the box...

What you choose to do from here on out is on you. I would recommend getting a NEW OEM alternator (2 is good too), adding a 2nd battery, and doing the big 3. I say new because its a 50/50 shot on getting a good one. Just the way the rebuild process works. The companies put in the same set of parts regardless of the issue. Sometimes it works others not so much.
These are electrical upgrades that really are imperative in high current applications.

 

I see what you're saying.
But it is doing all of this without the KCs even on, and it will only do it for the initial drop of voltage. Such as if I hit the brake pedal and it cuts off, it doesn't stay off for the length of how long I'm holding the pedal, it will come back on while the pedal is still depressed.
I was reading on the Powermaster site that the alternator doesn't turn on until a certain RPM. I know the battery is at least charging some because I haven't had any dead battery problems.

Also, on the tag on the new alternator, when tested at the factory it was putting out 90ish amps at idle rate, and 150ish at high rpm. Even the idle amp rate of this new one exceeds the high rpm rate my stocker would have been putting out anyway. Note that this truck is bare essentials, no AC unit or anything power hungry that runs off the alternator. The only thing electrical added was the head-unit, 10-disc changer, the two door speakers replaced, and now the KC's which are off 98% of the time since they only get used when wheeling at night (which isn't often at all).

Maybe I'll try disconnecting the KC's and see if that helps any, but they're never on anyway so I doubt it will.

Note: The radio would also cut off with the previous alternator for the previous owner when he had a plow hooked up to the truck. Whenever he would operate the plow, the radio would cut off as it is doing to me.

I'm not trying to shoot your ideas down or anything, I appreciate the help. But I just want to give a little more input in to see if any different ideas come.

Maybe I'll try to pull it into Electrical class and try to check the connections on the headunit with a multimeter to see which one is loosing power when it cuts off. Think this would make any sense?


Thanks


EDIT: Just got home from school. Worked fine around town, but right when I was about to get off the highway it started doing it again.
I asked my teacher and he said to try and clean off the battery terminals, so it might be that. I also just tried to see if it would do it with the engine off and the power on. It cut out just like it would with the engine running and the alternator spinning. So I am now leaning towards the battery terminals need cleaning rather then an alternator problem. Will post results of cleaning them up.

 

I had an old nova in the shop that had similar problems...everytime that he pushed his brake, the HU would cut off, also when he would have a heavy bass part the panel would dim on the HU...I looked it over and made sure all the connections were ok...My supervisor suggested that the alternator was not sending enough juice..I was skeptical and kept looking around...I found a fuse that was corroded, everytime he pushed the brake, his leg would move the fuseholder under the dash. So I took out the crappy old fuse holder and moved it to a better location and no more problems. Turns out the corrosion was sending barely enough juice to the HU to turn on, but when more voltage was sucked, the HU would cut out due to a lack of voltage. Check out all your connections

 

Well I pulled the HU out today to check the wires and whatnot. Looked like whoever put it in did a butcher job on it with the wires... the wires were just twisted and electrical taped together where they had to be spliced together. Undid the old tape, put new tape on and made sure the connections looked tight.
Found the ground wire, and there was a noticeable amount of surface rust on the metal it was grounded to, so I sanded out all of the rust and sanded down the connector itself.
Things seem to be working a lot better so far. I can pull my headlights on, hit the brake, hit the turn signal, shift through gears, without the radio cutting off yet. It did cut off a couple times still though, but I am fairly sure that is from my loose or slipping alternator belt. Sprayed the belt down with some dressing for the time being until I can put a smaller one on to fit tighter with the new alternator pulley.

So to conclude (for now), cleaning up the ground wire=problem solved (I think).