So I just replaced the alternator a week ago and the battery today. At idle when I have the headlights on (fog lamps too) the voltage drops from about 13.8 to about 12.25. Is this normal? It was worse (would drop to the yellow zone on the gauge) before I replaced the battery today and the guy at AutoZone said the battery was failing the "load" test. Should this happen at all? I checked the connections at the battery and they all seem OK. The cables are new. Should I check the engine ground? Where could I even find it? I can't find any details in the factory manual or my Haynes manual.

 

Also, when I start the car, the "door" and "fuel" lights stay on until I rev the engine.

 

Sounds like you got a crap alternator.

The stock alternators are 55-60 amp, which just isn't enough. Take that alternator back and get a GM 1-wire... you can choose 70-150amp alts.

Search for GM 1-wire... I've talked about it a lot on this site.

 

I feel like maybe the belt isn't tight enough. I have about 1/3 to 1/2 inch of play when I push on the belt in between the pulleys. I've searched Haynes, FSM, and this forum for tips on how to tighten it up, to no avail. I just don't see anywhere that I can shove a pry bar into for some leverage. Any ideas?

 

On top of the alternator to the side of the timing cover... pretty simple.

 

I assume you're talking about the top alternator bolt but maybe there's something I don't see. I was hoping there might be a tightening bolt or something (like the PS pump). I jammed a bar between the engine block and alternator and tightened it as much as possible, so hopefully that works. Maybe it's natural for the voltage to fluctuate on these cars, but I'm just not used to it yet. By the way, I replaced the battery because I measured it early in the day with a voltmeter and it registered 11.8 volts, and I measured it later in the day (I didn't drive it in-between) and it measured 12.4! So I figured there's something wrong with the battery...but maybe my new alt sucks too...guess time will tell. Hope it doesn't get worse!

 

check your battery cables for corrosion at the terminals. If you have those one size fit all clamp on types that lazy people use scrap them and invest the $15 in a set with real terminals. fortget needing a bigger alternator unless you are running some sort of exotic sound system. 60 amp is plenty unless you need to tell the other guys that yours is bigger than theirs. i've got a stock alternator on my 83 with an Interstate battery (not some optima crap that everyone thinks is neat cause it looks good). Been running that for 6-7 years never fails to start and run. since you have a new battery we can asssume it is good altho I did that once and spent a lot time chasing gremlins before getting it load tested. But good battery cables are overlooked too often. your ground strap should run from the negative terminal to a bolt into the body about a foot below the battery platform and then to the starter. Lots of lazy folk cut them off go straight to the starter which will work but not the optimum setup for reliablility.

 

I recently installed new battery cables, and I went right to the starter with the negative cable. I'll try to figure out how to attach it to the body and report what happens...

 

same thing happens to me on start up. I have to rev the engine for all the lights to go off. this happened after i messed with the dash board, i took it off to fiberglass it then this.
but its no big deal.
Btw it sound like the battery is your problem. in addition to the low out put of the stock alternator. if autozone said its not taking a load id buy a new one rather than getting stuck somewhere...

 

What was that NismoPick? GM 1-wire is a really easy solution?


Why yes son... I did say GM 1-wire! Thanks for asking.

 

get a short cable with battery terminal one end lug with hole on the other go to the bolt below the battery. get another cable with holed lug on both ends to go from there to the starter.

 

Agreed - I had a brand new Interstate battery a few months ago and was having the same problems as I did before I changed the battery. Battery would crap out after sitting for a couple of weeks or so. The voltage was steady when the Jeep was running but it still wouldn't hold a charge. Checked for parasitic draw and there was none. Turns out my brand new Interstate was faulty. The charging circuit is pretty simple - if there is no draw when the battery is hooked up and the vehicle is off and you have a good voltage output when the car is running it usually the battery. A load test at the garage will usually confirm that.

Check to see what your voltage is from the positive terminal to various parts of the body - make sure you've got a good connection. A bad connection or a bad regulator will give you voltage problems.

I most of my vehicles once the car is running at a cruise (get over idle) even with a load the voltage should stay pretty constant at around 14.4V at the terminals. My 370Z though changes voltage all the time although it does usually stay above 14.0V on the gauge (not sure how accurate the gauge is). It likely has some more advanced health monitoring systems for the electrical system.....

 

your belt has too much play, id go with near a 1/4". stock should be fine for a stock car, altho the gm is a very nice solution. i have one, but i have many extra accesories. do a voltage test at the back of the alternator, check it voltage grounded to battery. it should match the batteries voltage. if it matches, the wiring is good, if not time for some new wires. nissan has a nasty crimp joint near the battery from the alternator, if it corrodes, it will have issues. on my car ive been chasing crazy electrical problems for near 10 years.