Alternator Red Light
 

I have just recently had my cooling fan remived and bead blasted, it looks great. Anyway I have put the car back together now, started it up and now the red light on my dash is constantly on. When removing the wires from the rear of the alternator, i drew a diagram of where the wires went, so that when i refitted the alternator i would know where to connect the wires. So, im sure my problem would not be a case of fitting the wires in the wrong position. My question for you all is, What are other factors/faults I should be looking for? The alternator worked fine before the removal.

Alternator light
 

If you put everything back correctly the only thing I can think of is that your fan belt in not tight enough and it is slipping. When that happens alternator is not getting the RPMs it needs to produce required voltage. Hope this helps

You might try putting a multimeter on the batter terminals while the engine is running. When the light is on, it should mean that the alternator is not charging, so you should get 12V or less. I would re-check the wires that connect to the positive battery clamp. Did you remove the alternator from the fan housing? If so, then remove the alternator and make sure you didn't tighten it back into the fan housing in a way that cut an alternator wire. You have to basically go back in and recheck all of your connections.

The blue wire is grounded somehow. Maybe it was sliced, maybe it lay against the engine and melted. Disconnect the battery before removing the alternator for safety-- if the B+ shorts against the engine case it could be very, very bad.

Thank you all for your help, does anyone have a picture/s of how the wires are connected. As i said I did sketch the positions of the wires, and i am sure that i have connected them right; but just to be sure, a little visual aid may help me. Thanks

Perhaps a good wire brushing of the terminals and connectors for better contact would help. Here is mine before I removed my alt for replacement a couple years ago.

'81 SC with internal voltage regulator

http://forums.pelicanparts.com/uploa...1177848437.jpg

you've got the right advice here already, just follow it and you'll be set.

thanks for the pic 'terryh'

OK, so i took the alternator out and cleaned up all connections, checked the regulator and the brushes. Everything seemed fine. I put it back together, started her up, and after 3 secs the red light switched off! YES!!

Then I went to the local car wash to clean the car, started the car again and the red light remained on. I started it up a couple more times and the light remained on. Checked over everything, fan belt not loose. I checked the voltage at the battery terminal when the car was running and got 12.12V; And when the car wasn't running, I got 12.39V. Do these figures sound correct? I thought that when the car is running, the voltage should be around 13.8V.

Could the problem be my regulator?

BUMP!

I don't think it's the v regulator. My gut says you have something askew in a connection either at the battery (terminals/ related cables), at the alternator (fan housing connections, block ground, or a pinched or cut wire inside the fan housing), or between the alternator and starter. Time to clean and check all charging circuit connection and wires.

Your voltage while running, should be higher than when not running. Almost exactly the same voltage readings I had when my light started staying on. Replaced the alternator..problem fixed.

On my '85 the lugs and the posts were all different sizes making it had to screw-up.

Yea, check the mileage on alternator or just pull it and take to rebuild shop for testing. Output should be ~13.2v when running. Heck, have then rebuild for $100 with new reg.

Ok, so I have had the alternator rebuild, tested and works perfectly. After putting it back in the car, fire her up and the light is still on. This is beginning to really frustrate me. could it be a break in a wire somewhere?? Here is a pic of how it is wired.
http://forums.pelicanparts.com/uploa...1179384976.jpg

check and clean all grounds on the car.
if that doesnt work do what i did. after pulling the rebuilt alt at least 6 times in as many weeks.. Buy a K3

I have a '85 with built-in regulator but accoring to my Haynes manual on an '77. Red is output, Brown is ground (case), Blue is ALT light, Black is field. I can't clearly see the black and the second picture has buit-in reg. I should not that the reg in my diagram shows an old style relay type which toggles the fild on/off to get alt output.

ALT light is K2 in my diagram going between ignition switch (+12v) which is Red/Blk and Blue alt wire.

The light goes on when +12v from ignition sw is below the Blue sense wire from alt. The Sense terminal is a serrogate for the alt output which is connected directly to battery.

You could verify the voltage at each side on the ALT light but the low voltage at the battery has me most concerned.

when the light is on, your alternator is throwing out no voltage and you're reading 12 volts or less at the battery right?

I hope the shop that rebuilt your alternator had the good sense to test it first.

I still say you have a bad connection. You said that it was charging fine, light went off, and when you went to re-start the motor, there was a problem. I gotta repeat myself a little, so I beg your pardon, but this situation totally says to me that you have a bad connection (1) at the battery (2) the ground cable from the block to the fan shroud (3) a cut wire inside the alternator (4) positive cable from the alternator to the starter. You have a break in the charging circuit, in other words. I don't think you'll have much luck focusing on the alternator or regulator, in my own opinion.

Ok, sorry I haven't come back to you.

First things first. Your alternator is not charging the battery. Put the battery on a charger to bring it back to as close to 12.5 volts as you can, it's been drained by running the car. Diagnosis is impossible with a flat battery. FYI, a battery at 12.2V is about 25% charged.

Next. Since you had the alternator rebuilt and tested, let's assume the shop did it correctly. Which is by no means guaranteed, by the way. But for now, let's assume it's OK.

Do you have a multimeter? Electrical diagnosis is impossible without one. Get your multimeter, a 12 foot piece of wire, a short length of duct tape and a butter knife.

DISCONNECT THE BATTERY. If you don't, you could suffer personal injury or property damage. Remove the battery from the car so you aren't tempted to hook it up.

Now, cover the butter knife's blade with the duct tape and use it to CAREFULLY pry the oil pressure gauge out from the dash. Do NOT yank it out, carefully pull it out and turn it 90 degrees so you can see the wires going to the generator light. Now carefully ease the bulb holder for the generator light out of the gauge. Connected to one terminal of that you should see a blue wire. Disconnect the blue wire carefully.

Next, take your multimeter and connect the twelve foot piece of wire to one of the probes. Set the multimeter to OHMS and touch the remaining probe to the end of the piece of wire. It should read zero ohms when it touches, and infinite ohms when you break the connection. OK so far?

Next, disconnect the blue wire from the alternator and connect the piece of wire to the blue wire. Now put the probe of the multimeter on the blue wire going to the bulb holder at the gauge. Zero ohms or infinite ohms? Report finding here.

Next, connect the piece of wire to the positive battery cable, which is NOT connected to the battery, right? And then touch your multimeter probe to the red wire with black stripe going to the OTHER terminal of the bulb holder. Now switch the ignition on. Zero ohms or infinite ohms. Report finding here.

With this diagnosis complete you can decide whether to work on the wiring or buy a new voltage regulator. It's one of the two.

Good luck!

ok so the auto elec had another look at it, with the whole car this time. turns out the blue wire was open cct. there was a reak somewhere along it, i must have pulled to hard on it when removing the altenator. Blue wire replaced and alternator charges fine now. Thank you all for your help and suggestions.

John Cramer - Nice explanation - stored it for later, thanks.