I have been having a few electrical problems lately. Recently the starter would spin really slowly sometimes not even starting the car. Then it would just stop. Plenty of power and connections looked fine. Replaced the starter. All good for one day. I started my car up from getting lunch and all the idiot lights came on, I turned it off checked the alt belts and they were fine, checked the wiring connections and they looked fine. Had to drive it home so I went to get on the freeway and the lights went off. Hmmm. Now when I started it this morning I got the idiot lights. I tested output of the alt at the L terminal and it was around 8 volts. I went back into the car and revved it up and the lights went off and the alt then put out 14.2 volts.

So I am thinking the alt just finally is going out and it just happens to be a coincidence that the starter was just replaced. What do you guys think? It just seemed like it could be something else because of the recent starter replacement. It is an old alt though.

 

What you describe sounds like a failing alternator. Your starter may have been fine and possibly not getting full power since a failing alternator will discharge your battery more rapidly.

 

Yeah I'd say failing alternator for sure. I had this issue last winter.

 

Depends. You say you check the L terminal and got 8vdc. That SOUNDS like you looked at the terminal on the alternator itself. If so that's a mistake.

The L terminal wire in the harness plug is where the excitation for the alt fied comes from. You need to check THAT wire in the plug with engine off key ON and make sure it shows batt voltage.

Lack of voltage on the L wire in the PLUG usually means the alt will not charge. BUT this can be overcome by reving the engine up high and then the field will self excite itself.

Both wires on the alt small plug should show voltage with the plug off the alt.

Any of that make sense?

 

Thanks for the replies. I did check the L terminal with the engine running as this test says to. http://mazdarx7.iougs.com/electrical.shtml test #3, and I got 8 volts at first, then got in and revved it and it went up to 14.xx volts when I tested again at the L terminal. I will check in the morning if either of the W/B and B/W wires have batt. voltage.

 

Do the TEST SIX with all connectors connected. Should be what they say, 1-3 vdc.

Better to just pull the small plug off.......key to ON.........measure the wire that would be connected to the L terminal and it should show 12 vdc or whatever the battery has on it. And if it does that means when you do reconnect the plug to the alterantor that the field of the alt will be getting field voltage and the thing should put out when the engine is started. Output right away without having to rev the engine high to self excite the alternator.

Test number three was with all connectors on the engine and backprobing the L terminal wire and if the engine is running the reading would be approx 14 vdc give or take.

On a series four car the L terminal wire colore is WHITE/Black. It's fed from the METER fuse via the alt relay's coil inside the CPU near your left foot. The other wire BLACK/White is probably good since it gets power from the engine fuse and you say the car started and the car won't start with a bad engine fuse.

Both wire will show approx 12vdc until the plug is attached to the alternator and then the WHITE/Black on the L terminal will now show only 1-3 vdc. Normal

 

Ok with the small plug off the alt, key to ON, I get 11.48vdc at the L terminal, I get 11.98vdc at the R terminal, and my battery shows 12.19vdc.

 

Well doggies. Then when the plug is put back on the alt and the engine started the voltage output should go to approx 14vdc.

If it does not......something amiss inside the alternator imho. Lets say you put the plug back on and the alt still does not put out UNLESS you rev the engine high..and then it shows a charge. I'd say bad alt intenals. But before doing anything else I'd follow the site you've been using. Leave the small plug connected to the alt. Then backprobe the WHITE/Black wire with a meter lead. you might have to use a small piece of wire to do that or paperclip or such. Then key ON, engine OFF and see if the meter reads the 1-3vdc like it should.

One thing you might do. Pull that small plug off the alt. Pay close attention and make sure you located the WHITE/black wire in the plug. Now ground that wire. Use a paper clip or piece of wire bare at each end. IF the key is ON , engine OFF, you should hear the alt relay inside the CPU click........and as a result all the lights on the warning cluster should light up. Just my way of saying that when the WHITE/Black is put to gnd the idiot lights should ALL light up. That's kinda/in a way/sorta what happens if the key is ON, engine Off and the small plug attached to the alt. The white/black finds a ground in the internal circuit of the alt and that turns the warning lights on (idiot lights). The warning light panel already has power going to it, it's just looking for a ground to light up the light bulbs.

Long and short is that if you see the 1-3 vdc on the white/black wire with it connected to the alt and the alt does not charge when the car is started.......bad alt regulator imho. Even if you don't see 1-3 vdc but instead see five...six ...twelve volts.........that should excite the alt when it's turned and the alt should put out without reving the engine high.

You might take it to Pepboys/Autozone if it won't charge and see if they can determine if the alt reg has gone **** up. If you have the 1-3 vdc on the white/black and does not charge.....I say it's gone **** up.

But then again you know it will charge if its rev'd up high.....so that could buy you some time if your light on dough right now. Just rev it up to get it to charge and then take care of business.

 

check your battery?

 

LOL thanks, but yeah that was pretty much #1 on the checking list. I have a new alt on the way and will update the thread with my results on Wednesday when it gets here.

 

Had a similar problem, a nice forum member gave me a free alternator and my car is at 14.43 when its on. New alternator should help! also maybe clean battery grounds?

 

So to finish up this thread, it was the alternator. Installed the new one today she fired up with zero problems. I had really wanted to upgrade my alt if/when it went out, but I needed it back on the road. Thanks to all who helped!

 

That's good to hear~! :3