Altenator warning light doesn't work
 

I am getting charging through system and according to John Walker the circuit must work for the charging system to work.

When I turn the key the light doesn't go on.

How can I check the system and possibly find the source for the light not working.

FWIW the bulb is fine and all of the connections at the back of the light are solid. Also I had the motor rebuilt and the light was out before I pulled the motor and is still out. So, I don't think it's a connection at the back of the alternator because that would have been disconnected and reconnected when the rebuild was done.

Any help would be much appreciated.

bump

Carefully remove the tachometer without scratching the rim.

On the back of the bulb holder for the warning lamp there are two connections, one is a blue wire, the other should be a red with black stripe. With the key on, use a multimeter to verify you have +12v at the red/black wire. Then, disconnect the battery for this next step or you will weld yourself to the car, no kidding. Remove the alternator and disconnect all the connections. Then connect a jumper to the D+/61 blue wire where it connects to the alternator, and run that jumper to one probe of your multimeter. Put the other probe on the blue wire terminal of the bulb holder and check that it says zero ohms. If that wire's broken, report back.

Did you mean to say "remove the oil pressure and oil temp gauge".

FWIW I read through a prior post where you and John Walker were discussing confirming the circuit isn't broken by using a jumper on the blue wire coming out of the back of the warning lamp (actually you said from the regulator but I improvised). For s---- and grins I ran some wire from the blue (with a color stripe I can't recall) wire to metal and got a decent spark. The oil warning light dimmed at the same time.

However, in that post you guys spoke of how the circuit needs to be in tact for the charging process to take place. I have no problems with the charging circuit.

I was avoiding trying to pull the alternator but I guess it's down to that. I'll let you know.

Thanks John.

-Chris

Yes, I have been removing my own tach so much lately that I got locked in the rhythm.

Chris, if you ground out the blue terminal of the bulb holder, all you have proven is that you've got voltage to the "hot" side (the red/black side) which you knew anyway because the light was on!

You really need a multimeter for this kind of testing, they are so inexpensive it's ludicrous, I think I saw one the other day for $7 or something like that, they are available everywhere, auto parts stores, even community hardware stores. I actually carry one in the car they are so inexpensive, compact and lightweight.

Removing the alternator is an easy 20 minute job, the only thing that you have to remember is to disconnect the battery completely before you do it, don't want that positive cable falling onto the engine case and doing an impression of the firebombing of Dresden (Magnesium incendiary bombs). Somebody could have forgotten to tighten the nut on the D+/61 and it fell off or something, or left too much slack and the wires melted against the case, it's really easy to check. You may want to label the wires with a piece of tape to simplify what goes where, it's basically blue to D+/61, brown to D- (your SC may have more than one wire going to ground here) and the fat wire, I don't know what color it is in an SC but it's probably RED, to B+, the 14V output from the battery.

You shouldn't have to pull the alternator from the housing to check this, either. Just remove the fan belt using the tool from your toolkit so you don't break blades, and be sure to make a note of how many shims are on the outside of the pulley and how many are on the inside, you will want to get this right when you put it back together for the correct belt tension.

Good luck!

Thanks John, the plan is to tackle this tonight.

I've repalced my alt before but apparently forgot how quickly it can be accessed.

Are the contacts labeled as noted on the alt or do I need a schematic?

I got ya on the battery disconnect warning.

The oil light was the one that dimmed so checking for power to the alt light was probably a good thing albeit accidental.

John,

With the red and brown connected and the blue disconnected, I get spark when I touch the blue wire to chassis. Obviously this is with the battery connected.

With the alternator totally disconnected, a jumper from the blue wire to a multimeter probe and the other multimeter probe to the blue on the back of the warning lamp holder I get 6 ohms. This is with battery connected but key in the off position.

What next?

Might be as simple as the bulb is burnt out.....

I haven't replaced the bulb but the filament looks fine. Also, I have a piggy-back warning light and that doesn't work either. The bulb in that one is definitely good.

Before you go nuts taking wires apart, check the bulb for continuity. If the filament is broken there will be no continuity. Or you could try putting 12v across the bulb connectors. It would be prudent to actually see the bulb glow before you start dismantling your electrical system to look for faults. I have replaced a couple of those tiny dash bulbs that looked fine to my eye, too.

Well if the battery is fully charged, read at the terminals

12.5 volts @ rest
13.0 volts @ idle
13.5-14.0 2500 rpms.....

I'll check it all again just to make sure. Hopefully it's as simple as that. I would have done the bulb swap already if the oil press and alt warning lights didn't use different bulbs. To avoid pulling each gauge, which one uses the same bulb type as the alt warning light?

If I use a jumper between the hot (red w/black) of the alt warning light and the ground (blue w/red)(to simulate a properly functioning bulb) should my piggyback light function normally?

I jumped between the hot and the ground going into the back of the warning light. With the key on (oil light on) nothing happens. I'm assuming it should light if I jump those terminals.

What next? Thanks guys.

bump

Chris, jumping between the red/black and brown ground will just blow the fuse or light the car on fire. Please do the following.

Disconnect battery
Remove alternator.
Wrap B+ cable to alternator in multiple layers of duct tape and suspend away from engine parts
Reconnect battery
With the light hooked up properly, turn the key on and touch the blue D+/61 wire to the engine case. The light should go on.

If that doesn't happen, follow my original instructions for measuring continuity in the blue wire circuit.

Thanks John.

I got the light to work by grounding the blue wire at the back of the warning lamp assembly. Battery, alternator, and warning lamp were all fully connected at the time.

I didn't jump the red/blk and brown at the alternator.

As mentioned I did the test you described at the alternator except that I also had the brown disconnected (and taped up). I touched a jumper from blue wire to chassis (as opposed to the case as you describe). Should I redo it with the brown connected?

Thanks.

Ok, so the bulb works, but you still don't know if the blue wire is unbroken between where it connects to the bulb holder and where it connects to the alternator. That's what you are trying to figure out.

When you grounded the blue wire to the chassis, did the light come on? It does not matter that the alternator ground was isolated for purposes of that test, only that the key was on and the blue wire was grounded at the alternator end.

Key on, blue wire grounded: no light

Also, I am getting 12.5V across the battery with engine off. I get 14V at idle, and 14V at 2000RPM

wire trace time, from light to alt. a continuity check wouldn't hurt, end to end with a ohmmeter. maybe someone rigged the wiring different than stock.

6 ohms between the back of the warning light assy and the blue/red at the altenator. Should it be 0?

John Walker, we can abandon the PM chain and keep the discussion here if you would like.

What's the best way to trace the wire? Is the only break in the system at the voltage regulator (bulb to regulator then regulator to alt)?

In thinking about this more, should I just install a wire between the lamp assembly and the D+/61 terminal (to simulate what the blue/red wire does) and see if it lights? I suppose this could even be a long term fix...or is the regulator a required item in the path of the current?

Chris, in a stock 83 SC the regulator is in the alternator, so the "blue wire" runs straight from the bulb holder to the D+/61 terminal. It goes through a couple of connectors along the way which is probably where your problem lies.

So then this piggyback wire should light the bulb? I should have done this test when I checked the resitance but I didn't. Now I need to expose that back of the alt again.

What's the aluminum finned box next to the fuel filter? I thought that was the regulator and was assuming the blu/red wire goes into that and then onto the alt.

The aluminum box is the Bosch CDI ignition unit, it has nothing to do with the charging system. There are six wires going to it, none of them is blue/red. According to the wiring diagram, the D+/61 wire should be only blue.

Can you post some pictures? It seems like we are getting off into the deep end where a PO may have helpfully rewired with the wrong color making diagnosis like this impossible.

John, I haven't done anything with the CDI box.

My point with the CDI box was that I thought the wires went in there and I would check for break there...but clearly I'm wrong and the CDI box can be left out of the discussion now.

I have not checked any connections or wire colors anywhere but at the back of the lamp assembly and at the D+/61 terminal.

What are the connections that take place along the wires path from the back of the lamp assembly to the end that connects to the D+/61 terminal? Is it limited to the main harness connection or are there others?



I owe you several beers at the Glen in June.

John and John,

Any thoughts as to the best next step?

Chris, sorry to bring up an old thread, but I was wondering what your resolution was. You see, I have an 88 Carrera and need to start troubleshooting why my alt light does not come on.

My alternator does not excite until about 2700 RPM and then it charges fine, even at idle.

My alternator warning light does not come on, regardless of any variables. I pulled the VDO gauge and tested the light for continuity. The bulb is good (0Ω), and I also get 0Ω when I test the socket with the bulb in it. The connections are non corroded and the car is very clean, so I doubt a broken or corroded wire.

What should I test next? Should I just pull the alternator and check there after disconnecting the battery?

This has all the symptoms of an open in the warning light circuit.

The current through the light supplies the current through the field winding when the alternator is first started. After the alternator is spinning the diode trio provides the DC field current and the light goes out.

Usually in an alternator that has previously been used there is enough residual magnetism in the rotor that some current is generated at higher RPM and the diode trio starts supplying current to the field, just like it started up with currnet from the light.

To trouble shoot do exactly what JW suggested above. Verify 12 volts to the bulb, verify the blue wire goes back to the alternator. I like the step of grounding the blue wire and seeing the bulb light up.

Does the warning lamp bulb holder have a resistor across it per the bulletin to retrofit alternators with integral regulator to older cars?

If we assume a problem inside the bulb holder ... with the bulb not making good contact, then only the resistor is proving the excitation current, which would be lower than when bulb and resistor are in parallel, then the zero-Ampere speed would be higher than normal, and 2700 rpms would fit the pattern.

http://www.pelicanparts.com/catalog/..._tech_art1.jpg

http://www.pelicanparts.com/catalog/..._tech_art2.jpg

I had the exact same problem. I installed a volt gauge to check it all the time and noticed that it did not start charging untill I started to drive. I did all the tests and nothing worked. The blue wire was perfect and everything checked out alright. But the light would not work like it was supposed to.

I took the alt out and removed the regulator. I noticed my brushes were worn but not too far and my copper plates on the alt had grooves in it.

After months of working at it, nothing I did would fix it. Since my alt and regulatior were old anyways I bought a rebuilt alt and new regulator and installed it.

Problem Fixed! The red light and charging system now work just like they should. I guess I could have taken my alt to be rebuilt, but it was the type with only one wire on the regulator and not two.

I hope this expensive tip helps,

How old (miles) is your alternator? This may be a likely source of your problem also. Checking this requires removal of the alternator.

In my 88 cab the light worked OK but I had the flashing headlights syndrome at 60,000 miles.

Well, my alternator was rebuilt by the previous owners' mechanic in 2003, so I'm guessing that something is up at that end. Thanks, everyone, I'll start checking all these things out and report back.

murphy,

Well, worn brushes shouldn't show up in four years or less, but if they are marginal enough not to have continuity at rest ... sometimes vibration from the running engine will cause contact to start happening at the slip rings, and some Voltage output at higher revs.

Now that's interesting.

At the risk of hijacking the thread ... I went through charging light problems with my 73.5 a few weeks back

http://forums.pelicanparts.com/porsche-911-technical-forum/325072-73-5-charging-light-problem.html

and ended up replacing the mechanical voltage regulator with a solid state, and having the commutator on the (recently rebuilt) alternator turned.

It's all working great now, except that I've noticed the light doesn't go out at first start in the morning until I rev the engine to 2000 rpm for the first time.

I don't consider that a big deal, but since it's mentioned here ... the warning light comes on fine when the ignition switch is on but engine is off.

Perhaps the characteristics of the replacement solid state regulator are just different enough from the mechanical that I "should" replace the bulb or put on a resistor?

Chris,

Since I assume you are limited to the smaller 2 Watt bulbs, that is not a bad idea to install a resistor. <b><i>The Bosch Automotive Handbook</i></b> has a bit of info on the Zero-Ampere speed for alternators ... and says you can go as low as 68 Ohms at 5 Watts.

Yes, I'm limited to the 2W bulb. I'm just wondering if this is really worth it? The light goes out after the blip of the throttle.

Thanks!

The first try in my 88 cab I just replaced the regulator. All the usual excuses, I bought the regulator before I took the alternator out etc.

The slip rings in mine were in the condition described by rockaria . The new regulator fix, with new brushes, only lasted about 6 months before the headlights started flashing again.

The rebuilt alternator I bought the second time around seemed to have new slip rings and has worked fine since.

I wonder if your Previous Owner's rebuild was what I did or what the offshore rebuild company did. You might have to take it out and have a look. At least the wires will be easy to test with the alternator out.

Chris, from what I understand, the alternator must be "excited" to charge. On my 88 Carrera, the current flowing through the warning light bulb is enough to do this, so when the bulb is not closing the circuit, the alternator doesn't get excited until the alternator is spinning fast enough. So, really, it's normal for alternators to not charge until spinning fast enough.

Not sure if this helps, but it's interesting nonetheless.

Yup, thanks, I understand that. It appears that the alt gets plenty excited after driving off, just not at the very beginning. Or is that a too-simplistic interpretation of the charge light?

I admit to having odd turn signal behavior at stop lights (the signals work fine, the indicator in the tach doesn't). So perhaps the alternator does need a little more excitement in its life. (Boy, it's already in a 911, what more does it want?)

Yes, I should measure the idle voltage. It would tell me. I will.

Thanks, all.