Battery charge light will not turn off

I am having really big trouble with my 1991 Honda Prelude and it's getting to the point where I am starting to feel like I want to get it towed to the wreckers. I don't really want to do that but it's really taking the cake.

I hosed down my engine bay and the battery warning light came on and then an hour later my battery went flat. So far, this is what I have done to try and fix the problem:

- Checked the alternator fuses
- Fully charged the battery
- Replaced the alternator with a remanufactured unit
- Replaced the crankshaft pulley
- Replaced the drive belt


Today I checked the replacement alternators' B terminal with a multimeter and it's reporting just 3.84 volts! I thought perhaps the belt was slipping so I tightened it but it made no difference.

The only thing that I haven't checked is the air conditioner compressor pulley.

This could be a hint but it could also mean nothing... when I first installed the replacement alternator, the battery charge light no longer came on but the drive belt was squealing really loud. Then half an hour later, the squealing stopped and the battery charge light came back on again and has been on ever since.

What do others think?

I've gotten reman alternators bad out of the box.

Today I used a multimeter to perform tests on the alternator. I hope someone can tell me why the alternator is putting out 3.88 volts only.

All tests were carried out with the engine running at 800 RPM except for the last rectifier test, and the battery cable was disconnected from B terminal.

B terminal with alternator connector connected:

3.88 volts between B terminal and engine
3.89 volts between B terminal and battery negative post
-7.9 volts between B terminal and battery positive post
6.8 millivolts between alternator housing and battery negative post


B terminal with alternator connector disconnected:

0.93 volts between B terminal and engine
0.94 volts between B terminal and battery negative post
-9.74 volts between B terminal and battery positive post
0.64 millivolts between alternator housing and battery negative post


Alternator terminals (grounded to engine/grounded to battery negative post):

IG: Nil/6.2 volts
S: 3 volts/3 volts
L: Nil/6.4 volts
FR: Nil/6 volts


Alternator connector (grounded to engine/grounded to battery negative post):

IG: 11.5/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49/11.5 volts
FR: 11.81/11.82 volts


Alternator rectifier test with engine running:

Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -240 millivolts


Alternator rectifier test without engine running:

Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -933 millivolts

Is it just me or do others also see a grounding issue with either the alternator or the engine?

Further down in this article are more tips.
https://www.aa1car.com/library/charging_checks.htm

I just tested the voltage between the following:

Battery positive terminal and battery negative terminal
Battery positive terminal and engine
Battery positive terminal and alternator


All results matched, so the problem can't be bad grounding.

Does anyone know what else could be the problem?

It sounds like your reman alternator is crap.

Ow. What makes you say that?

Ow. What makes you say that?

I agree with Stealthee. The fact it worked when you first put it in, and now it doesn't. So what voltage do you get directly at the battery when engine is running?

Hmmm yeah, it working at the start and it not working now is strange. But there is another strange thing to this, when it was working the belt was squealing badly, then when it stopped working the belt stopped squealing.


I haven't recorded the figure of what I get at the battery but I do know that the battery goes from 12 volts to 11 volts once I start the car.

Hmmm yeah, it working at the start and it not working now is strange. But there is another strange thing to this, when it was working the belt was squealing badly, then when it stopped working the belt stopped squealing.


I haven't recorded the figure of what I get at the battery but I do know that the battery goes from 12 volts to 11 volts once I start the car.
Running you should be getting about 13.8-14.3 at idle. It sounds like the alternator seized for a little bit then crapped out.

Yes. Maybe.


Do you see anything abnormal in the test results?

Yes. Maybe.


Do you see anything abnormal in the test results?
Check the battery voltage when running. Otherwise you'll just be guessing.

So you don't see anything abnormal?

I think I may have found a clue. S should be 12 volts, have a look at S in the charging system circuit diagram.

http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/16-66.pdf

Now have a look at my test results of the alternator connector.

IG: 11.5 volts/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49 volts/11.5 volts
FR: 11.81 volts/11.82 volts

S isn't even hitting 6 volts, so there is resistance either in the wiring or the fuse. Does anyone know if this is of significance?

So the diagrams in the shop manual for the alternator terminals and the alternator connector are pretty crap and I thought the diagrams were of the alternator terminals but they are actually of the terminals in the alternator connector. I realised when the result I was getting on the multimeter from S at the under-hood fuse box wasn't corresponding with the result I got yesterday from S on the alternator connector. These are the correct test results from yesterday of the alternator terminals and alternator connector.

Alternator terminals (grounded to engine/grounded to battery negative post):

L: Nil/6.2 volts
FR: 3 volts/3 volts
IG: Nil/6.4 volts
S: Nil/6 volts


Alternator connector (grounded to engine/grounded to battery negative post):

L: 11.5/11.52 volts
FR: 4.58 volts/4.58 volts
IG: 11.49/11.5 volts
S: 11.81/11.82 volts


I don't know if the FR circuit to the ECU is 12 volts, but if it is then there appears to be a problem somewhere in the FR circuit.

To rule out the FR terminal in the alternator connector being bad, I followed it's WHT/RED wire to it's socket at the top right hand side of the engine bay, disconnected the connector that connects to the socket and then tested the FR terminal inside the connector.

https://i.ibb.co/0Y1ShrJ/FR-at-top-right-hand-side-engine-bay-connector.png

These are the results:

FR at alternator connector: 4.55 volts
FR at top right hand side engine bay connector: 4.94 volts


What do others think?

You've done lots of testing. It appears you have convinced yourself the Alternator is good. Until you test that alternator, the numbers won't mean anything. The first step in testing the charging system is an alternator test. Either running or pull it and bench test it.

Never mind, I the FR voltage is fine.

I can now confirm the car is good and the alternator is fucked. The place I got it from is sending out another one to me.

Thanks aleekat & Stealthee for the help.

Never mind, I the FR voltage is fine.

I can now confirm the car is good and the alternator is fucked. The place I got it from is sending out another one to me.

Thanks aleekat & Stealthee for the help.
That's good news. Since you're probably getting another Reman. I would bench test it before install.