Relay Testing

[esh1071]

Hi All:

I have been visiting this forum for nearly a year and it has been very helpful on various items. This is my first post and I need some help. My alternator recently died and I had it rebuilt by a local guy that does very good work. I reinstalled the alternator, but the battery discharge light is still on. They did a test at an Advanced Auto and said the alternator is not charging the battery. I'm positive the alternator is good because the repairman did a test on his machine to show me...... anyway, I thought it could be a loose ground but haven't found one. I've checked several things to no avail at this point.

I've come to the conclusion that it is a bad relay, but I do not know how to test the realys. Can any of you tell me how to test the relays? Thanks in advance for any help.

Eric

[alsalih]

Have your alternator tested at two other shops before ruling out a bad rebuild. These Advanced auto places don't always have know ledged people working these test machines. You really should have used a multi-meter to test the voltage at the battery with the vehicle off and with it running (should be 12+ Volts off and 14 plus running if the alternator is working right). I would check battery (for internal short) and fuses before going after relays.

[SKperformance]

There is no relay for an alternator it is all internal for power output.

It is either a bad wire ,alternator or your battery is causing some problem.

Have you tried running the engine without the battery hooked up to see what the voltage is and if the discharge light goes off?

[obergc]

Eric,

There are no relays in the charging circuit. It is a pretty straight forward circuit. There are two electrical connectors on the alternator, a terminal stud with two white wires connected and a separage 3 pin connector. Pin 1 of the 3 pin connector has a solid yellow colored wire connected and that wire turns the "no charge" warning light on through the alternator internal IC regulator. Pin 2 has a black/yellow colored wire and that should have battery voltage on it that comes from a 7.5A engine fuse that gets power from the ignition switch in the "run" position only. It should be 0 volts in the OFF, ACC, or Start position of the ignition switch. Pin 3 has a white/blue stripe wire that should have a constant battery voltage reading that comes from a 40A fusible link that is located by the left fender in the engine compartment. The heavy white wires on the alternator terminal stud connect to a 120A fusible link in the same fusible link box. I realize that it will probably be difficult to access the 3 pin connector with the engine running. With the engine "NOT" running, I would get access to the alternator connectors and with a DVM, measure voltage on the terminal stud and the white/blue wire pin for a battery voltage reading, I would then turn the ignition switch to the run position without starting the engine and then measure for battery voltage on pin 2 with the black/yellow stripe wire. If you're reading good battery voltage at those 3 points, the alternator or the alternator internal IC regulator must be bad.

[esh1071]

Thanks guys for the input. I have checked the 120A and 40A fusible links and the 7.5A ENG fuse and they all seem to be ok. I will double check them to be sure. I also took the alternator back out, as I was afraid I may have inserted the 3 pin connector incorrectly. After I did this I realized the 3 pin connector will only insert one way. I put the alternator back in taking special care to make sure no ground wires touched it or that there weren’t any bare wires showing.

Probably a dumb question here, but in reference to SK’s post, how do I run the engine without the battery hooked up to see if the discharge light goes off? Wouldn’t I need power from the battery to see if a warning light is on or not? Sorry If I seem inept here. I’m decent at working on cars if I know the problem, not so good on the actual trouble shooting part. Thanks again for the help.

Eric

[SKperformance]

When the car is running it always uses power from the alternator ,the battery is only used for starting and residule power when the engien is off.

Other than that it is just being charged when the car is running.

If the light comes off it means the batteyr has some problems with the lead cells causing too much resistance.

[esh1071]

Thanks everyone for your help. I've been out of town and haven't been able to respond. To give you an update I checked all the fuses (they were ok), I tried a different battery but the discharge light remained on. I checked the terminal stud and 3 pin connector with a DVM and those checked out ok. I took the alternator back to the repair shop this morning and the repairmen agreed that the problem was most likely the alternator regulator. He is going to work on it again. I won't get to put the alternator back in until Monday, but I'll update you if that takes care of the problem.

Thanks again for all the help. Wish me luck on Monday!

Eric

[wwest]

First....!!!!...STOP!!!!

Never, NEVER run your car with the battery disconnected. The battery is an integral part of the time constant of/for the voltage regulator. Without the battery you will get HIGH voltage spikes out of the alternator and those spikes can very likely do permanent damage to the various electronic modules, ECU's etc, in the car.

Second, the actual core problem for a 93 LS is most likely that the slip rings are worn clear down to the steel alternator shaft. That's what I found on my 92 LS just months ago at ~100k miles. Apparently the slip rings are made of really soft copper as my slip ring brushes had lots of mileage left.

Since it is such a very RARE thing for the slip rings to wear out before the brushes themselves your alternator repairman may have never suspected/checked those. As for myself I went to Lexus and bought new brushes before I even removed and opened the alternator since my lifelong experience is that the brushes will wear first.

[lenore]

I agree, never run car without battery, the Regulator in the alternator looks for the B plus voltage from the battery in order to work properly. And I suppose spikes might happen, but I doubt it.

[SKperformance]

You are not running the car on the road.

The battery comes into the circuit as a buffer or capacitor .If removed the alternator will continue to work as normally it would only spike if for some reason you turned on you fan at high speed. The regulator is not made for spiking anything.

So for the matter of layman's testing it will be fine to disconnect the battery terminal for a few seconds to note the differences .

[Leadfoot]

Absolutely, positively, never ever ever run it without a battery. The thought of it just makes my wallet cringe!

With the engine running does the battery terminal voltage equal 13.9~15V at 2000rpm? I don't expect so as the charge light is on. Therefore you will want to check the round connector with three pins going into the altenator. One of these pins should have 0–4 V to ground WITH IGNITION SW AT ON POSITION AND ENGINE NOT RUNNING. If the alt. regulator is not getting juice the proper output voltage for the system won't be generated.

My altenator was taken out by a failed steering pump. It will pay to work out what killed yours.......

Good luck

Leadfoot.

[lenore]

You absolutely should not unhook the battery after starting the engine. this could cause a spike which will destroy the regulator in the alternator. It is true that after the car is started the field voltage is provided by the alternator itself, but their is a leveling effect fromthe battery as the voltage from the alternator is not pure dC but pulsating DC in a three phase pulse from the regulators. It could cost you an alternator (Murphys law) if you go by SK's comment. If the battery is measuring 13.5 to 14.5 volts while the car is running the alternator is performing. The voltage should drop to 12.0 to 12.5 when the car is turned off.

[esh1071]

Hello Everyone:

Just wanted to give you an update....... after taking the alternator back to the repairman he determined that there was a bad brush inside. He replaced it and I installed the alternator earlier today. The battery discharge light is now off and the car appears to be running fine. Just wanted to say thanks for everyone's input. Hopefully everything is now taken care of.