When i first got my s4 everything was fine as far as electrical. i put a sound system in the car and then my altenator died. i took the system out of the car as soon as this happened and put a new altenator on it. ever since my volts have been really crappy and every time i come to a stop at night my lights will dim to where i can notice it and my guage will drop down to around 12.5-13. when i need to use heat or wipers it will drop down to simply battery voltage.... around 12.3ish. i have since then replaced the battery.... not to mention i an currently on my 7th altenator since this has happened i have done some voltage drop test and the only thing that i can find is that there is .8 volts of resistance from the altenator ground to battery ground...... by what i know that isnt enough to cause this issue. if anyone knows any similer problems and how it was fixed or if someone has some suggestions i would greatly appreciate it as i am in dire need of help!!!!

 

The alternator grounds to the engine through its mounting, thus there is no need for a ground wire to it. Secondly, aftermarket alternators are widely known as being rather insufficient for doing the job. Some owners will upgrade to the 3rg gen alternator and there are many writeups explaining such changes. Also, make sure the belt is properly tensioned and that the body ground for the battery/charging system, found at the driver fender, is up to spec. And testing the voltage output at the alternator might give you a more accurate reading then provided by the voltage gauge.

 

are you sure you have the correct pulley on the new alternator? Alternators need a minimum rpm to work properly and if you put too large of a pulley on the new alternator it would spin too slow at idle to properly generate the correct voltage/amperage.

I have an s4 alternator that was tested in working condition by autozone and came off a car with a lol'd apex seal. $30+ shipping and it's yours. Also have a tested S5 alternator but I couldn't let that go for less than $50.

My gauge on my s4 is pretty accurate, however, my s5 car says 8ish volts when it's actually around 12.5, and says 12 volts when it's running down the highway... which is actually 13.8-14.4. Stock gauges are not completely accurate.

If this was my car, I wouldn't see this as a problem. I never take short trips or let my car idle for long periods of time; my battery is in good operating condition and can supply current for more time at idle than my fuel tank could supply fuel.

Now, for a rant...

>installed a sound system large enough to fry his regulator/rectifier
>cant use a multimeter (see: measuring resistance in volts, not ohms)
>has changed more than 2 alternators without looking into the root cause
confirmed for high-school dropout

 

Id be worried about any voltage drop on ground circuits. Grounds should have 0.01v drop and about 0.2 ohms. What about drop across engine ground?

 

well nicdchris.... sorry i said resistance i did a voltage drop test and either way that is too much of a drop. and yes i did put too big of a system in and did fry the altenator... i know stupid mistake. and as for putting a bunch of altenators on.... it was my daily driver and i go to school for double the hours of most people and work full time so i couldnt really look at it. not as dumb as i may sound i've taken to school and had people/teachers look it at. granted they didnt go all out on it but the only thing they could suggest is the large voltage drop on the ground wire.

but when i got the first new altenator it had the same size pulley as the one off of my car. everyone after that has had an 1/2in smaller pulley which caused me to buy a shorter belt and thats what ive been using ever since so im still pondered by that????

also as far as my gauge goes it reads pretty much exactly the same volts that the altenator is putting out.

and i havent check the drop across the engine grounds yet.

i wouldnt really care too much about this whole thing but it is extremely annoying when you come to a stop and u watch all of the lights inside and outside of your car dim.

 

Btw doing a voltage drop test is a way to check for resistance in a wire and can actually provide a better reading bc it is performed while there is a load on the curcit so maybe u should know what your talking about before trying to make someone look stupid because it made u look dumb and rude and as far as a high school drop out.... That's a joke I'm in college and I have 2 ASE certifications...... What do u have? Bc Idt u do..... Also one of the ASEs being in A6- electrical and electrical systems..... So how do u feel now?

 

If its a rebuilt alt I can guarantee you picked up one with a bad Diod pack or voltage regulator inside. Autozone thinks their technicians cause their little handy alt tester says its ok. But their tester doesn't test internals. Go return it and get a new built or test a chance with another one.

Save the hassle on diagnosing.. The charging system on rx7s is quite simple since theirs no fusable links.

Rx7 alts are rated for 60amps I believe. That should be enough to handle abuss. Given the highest amp pull besides a speaker amp would be ur blower motor on high around 20amps then your fuel pump. If your dimming lights then either you got a bitching sound system that cracks windows or your alt isn't putting out 60 amps and your dipping amps from your battery.

If you wanna get technical unbolt that 8mm wire near the engine lift braket and on the alt. And check your current output from that post to that wire. Then start checking that wires resistance to the positive term. The major ground wire that ground the engine is mounted to the top bolt of the starter under your steering column. aaroncake has a nice write up on grounds

 

Btw rising rpm made a bracket that mounts a gm 100amp alternator. He states he's getting the opposite effect from your problem as lights and such get brighter the higher revs you go lol

I forgot to add test parasitic drain. And you can possibly have a dead cell in your battery that also be pulling amps from your alt. I wouldn't recommend this because ive seen pcms fry but you can try running your car and accessorys on just the alt once started and see if conditions improve. Or run it with a jump box instead of a battery

 

I think they're 90 amps but either way it’s more than enough! And I’ve been through 6 alternators so either all remans are just super crappy or I have some sort of issues. And I want to buy a brand new one not reman but I can’t find them anywhere! and it was a bitchin system lol but as soon as this issue started to occur I took it out and have never messed with it again so that isn’t the problem. And I have done a parasitic drain test and its good nothing more than a couple millivolts. And about 6 months ago I took the car into my school shop and tested the battery on a loud tester and it also tested good but I could also go and get a new battery and alternator at any time because they’re both under warranty still. But it seems like everyone keeps pointing me in the direction of the main grounding points of the car so I guess that’s where I’m going to have to start the next time I get some free time.

 

You can temporarily unplug the brake light switch from the brake pedal and see if the lights still dim when braking and idling. If they don't then the brake lights are likely pulling too much amps from the charging system. Could be dirty bulb sockets and or the wiring having too much resistance.

 

The third gen alt will for sure help but it sounds like to me you might have a wiring problem I would run down the wires from alt check for breaks or loose connection's!

 

I will definitely try to unplug the brake lights as see if that helps but I think it does it even if I rev it up and let the rpms drop but ill double check tonight and post what I find out and ya I think it's a working issue too so I might print off a wiring schmatic and try to tace the wires for the charging systems and look for breaks/loose connections

 

So last night I did some looking around on the 7 and I found a couple places that I thought could be grounds but idk which one is the MAIN ground..... If anyone could be a little more specific as to its location or maybe post a pic of it. It would be greatly appreciated