alternator indicator light via blue wire?
 

hi guys . i know there are tons of alt./charging threads on here. but i need answer to simple q. if the blue wire is NOT hooked up to the bulb, does this mean the alt. will not "activate" and charge?

what should the bulb wiring circuit look like to the blue wire? (this is a race car and everything is gutted so must wire separately from a harness)

i i thought this blue wire was simply for an indicator./idiot light and not needed. so it has not been hooked up. but its seems TO BE important. from my reading on here. so maybe i am the idiot.

74 911 RSR. PMOS MSD DISTRIBUTOR

The circuit (Alternator/blue wire/light) needs to provide the proper resistance to excite the alternator. Here's a link to a thread that discusses adding a diode to cure run-on and resistor to cure excitation issues.

https://forums.pelicanparts.com/porsche-911-technical-forum/989178-electrical-wizard-help-needed-alternator-light.html

regards,
al

I guess the question is what alternator do you have? I have the wiring diagram for the '74 if you need it. If you have the newer style alternator with the internal reg, then I guess you need to do the update as mentioned in Al's thread.

I think you have the answer. In my case, I use an aftermarket bulb from Dorman.

It is similar to this: https://www.dormanproducts.com/p-8652-84914.aspx?origin=keyword

I just use the blue version. I used to buy them at Radio Shack.

Here is a story that can help you understand how this warning bulb can be helpful.

A few years ago I was out watching some PRC friends racing at Sears Point. One Spec 911 started misting a bit of oil. I was in race control but not in charge. It was decided that the oil wasn't enough to black flag the car. Seemed ok to me.

I cannot remember whether the car finished or came in early. But I do remember seeing it when it came in. The entire back of the car was covered in oil. There was no oil in the engine, and the engine was clearly damaged.

What had happened is that the belt broke. Remnants got tangled behind the crank pulley. The crank seal got compromised. That is how the oil was coming out.

The driver had no idea. No alternator warning light was installed.

If I recall correctly, it was a fairly new engine.

The driver, an old friend, decided that was it and retired from racing. He sold the car and the trailer to a friend. That car will be for sale soon as a street rod.

Here is a pic of the 2015 version of my dash, showing the alt warning light I use:


http://forums.pelicanparts.com/uploa...1559067169.jpg


I highly recommend inclusion of such a warning light. The resistance creates the excitation for charging, and it can be helpful to know if/when you have an alt. problem whilst driving.

thanks mike and all... ( i just emailed you mike ) . yeah thats a frightening story,... lost belt at daytona a few years ago, and did not have an indicator light.... and did not realize until temps skyrocketred

so in wiring the bulb, does the blue wire just go to one side, then the other side of bulb to ground?

so it lights when engine is fired, then shuts off when charging kicks in?

(i can clone any gene, but i am severely electron flow-challenged so please bear with me....)

so mike . i guess that dorman bulb provides adequate resistance to create the excitation for charging.. and thus does not need the additional resistor mod. that al iksmal posted?

thanks

Here is a dwg that may be helpful:

http://forums.pelicanparts.com/uploa...1559068550.jpg

Yes. That bulb works fine. I think I may have a few extra if you cannot find one.

perfect mike . thanks. stay tuned will report. i cannot believe its this simple a fix..., but thats what they said about the human genome....

The circuit works because when the blue wire voltage dips too low or goes to zero, the bulb light up. So just like the factory bulb set up.

I doubt what you are experiencing is due to battery voltage fluctuations. But of course I again strongly suggest having an alternator warning lamp. Of course this can also be accomplished without a bulb at all if you have an AIM or similar dash with an available analog input line.

You'd just feel up that blue wire and say set a voltage threshold at 11-12 volts or something similar to trip an alarm.

I have the blue light on my dash panel AND and alarm set in my AiM MXL2 dash if the voltage goes below 12v.

thanks mike and scott. excellent! i just got a new AIM MXG and am looking for ways to utilize all the inputs. mike: love that custom, simple CF dash in your car.

simply cannot believe that lack of this simple, low volt, " excitation " charge is causing all my problems..... so germanic....

but . thats the hypothesis... .. stay tuned and thanks again.!

frank

Reporting in from the field. Based on so many reports of MSD boxes overheating/going bad... i bit the bullet swapped them out for brands new ones, ran all new wiring, . also hooked the friggin little blue alt. wire up to a light. This thing is great! comes on with ignition on, ( as i have it wired) . Then when alt. kicks in at start it goes out. . very nice indicator to have on dash! ..

at 3000rpm in my garage i get 14.7 volts across the battery terminals., so to me, the alt. is working.

unfortunately . does not seem to have solved any problem... engine still misses and backfires up thru midrange. i do not yet know if it will cut out after a few track laps... but will see on tuesday.

i also checked fuel flow thru and past the pmo regulator and into the carbs. all is fine. no blockages. good fuel in pmo windows.

at rest in garage, i have AIM afr readings of 16-17. at odles . 1000rpm... they go down to 13-14 when revs are up to 3500 or so. but this still seems high. at that rpm. motor is still backfiring.

These are race cams along with 12.3 hi comp motor. not sure this makes a difference.

i am at a loss as to what to do next if this does not solve. cap, rotor, wires?

Cause of problems
 

Well Friends . yes I am an idiot. Thank you for all the help. Turns out There is a huge blockage in the fuel pickup . inside the kevlar box of the fuel cell. i thoroughly cleaned kevlar lining , installed new foam, and also thoroughly vaccuumed, i thought, inside the fuel slosh box. you cannot see in there, alll you can do is feel. and i thought the intake was fine. turns out the plug . which seems to be MOUSE FUR!! was stuck way in there. so it might have sloshed out over time, allowing some fuel past, then rejammed up on track in first few laps.... at least i now have two extra coils, two MSD boxes spare, another rotor and cap....:rolleyes:

David Murry told me this is the laboratory mouses cousins getting revenge! as i do molecular genetic studies on mice with cancer.... and tend to off alot of them...

BTW ... i had 14.2 volts across the battery at 2500 rpm. then when i had the blue wire hooked up with the indicator bulb, it was 14.7 . even so, very nice to have the charging indicator light working on the dash.

:D:D

http://forums.pelicanparts.com/uploa...1560457006.JPG
http://forums.pelicanparts.com/uploa...1560457006.JPG

Thanks for closing the loop.

A few years ago, when I was returning to racing after a 4 year hiatus, I had a similar issue. I had a new racing engine which my friend/engine builder and I broke in and initially tuned on the mountain roads in Truckee.

I was twin plugged for the first time.

That all went swimmingly.

Then we tried to fine tune the map at Sears Point (sea level). The mixture was fine, but there was a strange "miss."

I did some trouble shooting at the track. I started with ignition, and then looked at fuel pressure and flow rate. Also looked at charging. No joy.

My time was limited because I needed to head down to RR V at Laguna that same day.

At the next event, the issue got worse right away in Friday testing.

Finally, Sunday morning I decided to open up the cell. The final frontier.

Now I have to say that when I parked the car four years earlier, I had drained the cell, and inspected it. It had a year-old Fuel Safe pickup hose and sock.

Everything was clean and tidy when I put the car away to start the hiatus.

Well once I got the cell open, I found that the very top of the pickup hose was partially disintegrated.

I had no reason to think that could happen to the pickup hose sitting dry for 4 years. Again, it was only about a year old when I started my hiatus.

The folks at JWM had some hose so I was able to get running in time for one last session on track for that season.

Fuel Safe used (and still uses) Aeroquip socketless hose for at least some of their pickup products. Apparently it did not like to sit dry for four years.

Congrats on finding your problem.

Sending you a PM.

As we all know, the alternator belt is more than just a charging system. That vital cooling fan is way more important for keeping the engine in working order. I can drive a long way with to charging alternator, but only seconds with no cooling.

I just modified my tachometer, well OK I had it done. I put in a nice volt meter in place of the stupid shift light. It looks like what the factory should have done. Now I know for certain the alternator is turning and making voltage, and most important the fan is turning. It was not that expensive and orders of magnitude cheaper than a new engine, or a tow bill from driving with a bad or under performing alternator, or one that is putting out 15 volts are frying the electronics.

1) The "theory" on why the alt light goes on or off is pretty simple. With the engine not running (or the alternator not charging, for whatever reason), the 12 volts (nominal) supplied to the dash light from the battery sees a ground at the alternator end of things, so the bulb lights up. When the alternator pumps out 12 volts (nominal), the voltage on each side of the bulb is the same, so it won't light up.
2) A good thing to train yourself to do, track or street, is to turn the key to the run position and look to see that the alternator light (and the oil idiot light) are both illuminated. That means that both of these warning systems are working, and chances are good that the voltage regulator for the alternator is also working. Because when the VR goes bad, typically the light will not come on. Same with the idiot light. It is hard to look for a light which indicates trouble if it doesn't come on - like the hound which didn't bark in the night.
3) The easiest way to add a volt meter to our cars is to buy one which just plugs into the cigarette lighter. US lighter receptacles are (or at least were) a bit narrower than German ones, but it is easy to shim a plug-in device as needed. No wiring, no mounting. A voltmeter can also tell you if the alternator is putting out too high a voltage - if you see 15 or so volts, the regulator may be going out, and you may start frying your battery.

http://forums.pelicanparts.com/uploa...1560542431.jpg

I 100% agree with Walt. Check you bulb regularly at startup. I did not like the out of place look of the digital volt meter in the cigarette lighter. It works, and is inexpensive, so I will not say it is wrong. And it was out of my normal field of view.

What works best for me may not be your choice. I like the look, and the function of the gauge right in front of my face. It looks "right" and gets rid of the silly shift light on a Carrera. It is just wasted empty space on a SC. I also have calibrated numbers on my oil temp gauge. Once again, I am a type that likes solid information, and the "second white line" is something I can think about and arrive at a number, but just looking and seeing 185 is a lot less thinking.

What works for me is not a one size fits all, and you may think it looks terrible. I don't care. It is my 911, and I set it up the way I wanted. I sure don't try to tell anyone this is the only way.

Glen - what tach has that voltmeter so nicely located in it?