What's the quick and easy way to check the alt out put?

[Zeke]

One of my problems (well, the only one keeping me off the track tomorrow) is low to no alt output.

Now my car doesn't have half the wires of a stock wiring loom. If that. But the alt harness is intact, rebuilt alt and new regulator. Where is the exciter wire? Should one of the 3 pin connector be hot with ign on? I'm showing 0.14 volts on the red, 0 on the other 2.

Alt light is off at over idle, but comes on if I use any voltage, like brake lights. System reads 12.1 volts running.

Did I leave out a hot wire back to the relay panel? Should there be voltage at the regulator with ign on but not running?

Give me some check points, please. I didn't search this because I don't have the stock wires, but I might have all I need with the relay board and the stack alt harness. The one the was stripped out was the main thru the tunnel harness. When I got the car 2 years ago, this was all melted together.

Someone said ove on the 911 BBS that you could trick the voltage reg to determine max output on the alt for about 2 seconds. Anyone know about this on a 914?

[Dave at Pelican Parts]

Yeah, you short the field wire (DF) to positive (D+). Check the diagrams for which wires those are. It's a good way to heavily tax your alternator and to start overcharging your battery.

If you're getting 12.1V across your battery terminals (the posts themselves, not the cables clamped onto them!) then you are discharging your battery. And it's just about dead. A fully-charged battery should show right around 12.65V across the posts; a deader will show just about 12.0V. A working charging system should show you 13V at a minimum, and more like 14V or 14.4V, which is the nominal system voltage for a "12-volt" system.

The quickest and easiest way to check the charging current is with a really massive ammeter (capable of handling several hundred amps because of the load from the starter) between the battery ground post and the battery ground strap. The next-best is an inductive ammeter on the ground strap or the (+) cable. Next best is... Hmm... Probably inferring from the voltage as I did above.

--DD

[Zeke]

Thanks, Dave. I can refine my parameters a little. I have 12.58 at the battery terminals. Stopped, running, whatever. I'm not seeing any charging (or discharge). I t doesn't take much voltage to keep the coil happy. That's the one power draw I have unless I use the brakes.

Since my last post, I've lost the alt light. I found an old post of yours about plugging the alt harness directly into the reg and jumping over to the blue from the red. I jumped the other wire, not the green, by mistake. Game over, I guess.

[Scrappy]

It may be to late, but the easiest way to check for output is to measure voltage across the battery teminials with a VOM with the car shut off. Record voltage.

Start the car, again measure voltage. It should be around 13.6 volts. If it's the same voltage as above - it ain't puttin out.

[Zeke]

OK. It ain't puttin' out. What do I blame first, the reg or the alt. Both new.

[Dave at Pelican Parts]

Short the DF and D+ wires together. If the voltage on the battery terminals then goes to ~16V, make sure the wires to the regulator are good and then swap in a new reg. If not, make sure all your wires are good, check the alternator belt for slipping and tension, and then drag the alt off to have it tested.

--DD

[Dave at Pelican Parts]

Hmm, from your post on the other thread you have shorted those terminals together and the alternator does work.

OK, that's good news. Now you have to find out what is going on with the wiring. The alternator warning light is a vital part of the charging system--it is part of the way the alternator "jump-starts" itself. The light needs to be the right one as well; if the wattage (and therefore the resistance) are wrong your charging system won't. So trace down the wires and make sure that the blue one that plugs into the warning light has continuity with the D+ wire (red?) going to the alternator. Or at least to the plug where the D+ wire goes when the alternator is plugged in.

Then check that the bulb is the right kind. Not sure how you do that. I think Jim Thorusen's article in the Tech Articles section lists a resistance or power rating for the bulb.

Check for ground on the plug where the brown alternator wire goes. I think the red wire gets +12V when the ignition is on; make certain it does. Remember to clean up the #8 (is it #9?) fuse and holders.

--DD

[Zeke]

It looks you you and me on this one, Dave. At this point, I have traced the problem to the relay board, I think. There is no voltage to the light. I guess what you are saying is that the blue wire needs to be energized through the resistance of the bulb. I've checked the bulb and it works and it did work at one time yesterday before I started messing around. If the voltage to the bulb is supplied by the other wires to it, that's my problem. But, either way, no action at the bulb.

Seems amazing that the current from the resistance side of the bulb is enough to do anything, much less, be the exciter for the alt.

[Zeke]

Originally posted by Zeke


Seems amazing that the current from the resistance side of the bulb is enough to do anything, much less, be the exciter for the alt.

That was it!!

I had no power, for whatever reason, to the circuit that powers the oil light, low gas light and alt light. I haven't run it and tested my charging, but I have an alt light now. So, that means there's power back to the relay board via the blue wire which is on the resistance side of the alt light. You know, that just don't seem right. But, that's how it works, my friends. Some times I wish I had a '34 Ford coupe.

[PBJauker]

sometimes bad fuse or bad contact at fuse

[Zeke]

Here's the latest. I'm definately having an inordinate amount of trouble with this.

I got the alt light back along with the gas gauge, etc. Now when I run the car, the light is dull at idle and gets brighter with aceleration. Is this a recognizable symptom? Or, am I to just throw out the baby with the bath and replace both alt and reg?

PS, I don't think my output test for the alt was valid. Can anyone tell me the colors of the DF and the D+ wires? I'll do that again, although I probably cooked things doing that.

[Dave at Pelican Parts]

DF is green, I believe, and D+ is red. Hopefully you didn't cook anything...

I think thta dim at idle and brighter as the revs increase means a shorted diode in the bridge inside the alternator.

--DD

[Zeke]

Dave, I keep going out and fooling with it. I found the wires on the silly schemactic. You are correct on the colors as far as I can see. I did the short test once again. No charging. Out comes the alt.

You know what's super frustrating? I JUST INSTALLED THE ENGINE LAST WEEK!!! I could have done this so easily on the stand. But, the thing was just rebuilt, so I assumed it was OK.

Or, did I blow the diodes? You can do that by hooking up the battery backwards, right? Well, I don't remember doing that. So, something else maybe. I'll ask the next alt rebuilder how and why that happens. I'm not sure I trust the first rebuilder anymore.

Thanks, DD for all your help. Hopefully, this will serve others well in the archives.

Edit: In the end it was the diode. I don't know if I did this or not as the brake pedal and light thing was happening before I toated the motor.

[Brant]

No intention of hi jacking the thread...

but for my own sake; is there a test to see if the regulator is good/bad, other than putting it into a running car..

In other words, is there an ohm meter test or something I can do to check out a used regulator.. say at a junk yard?

brant

[jamcleod]

alts need current to energize the magnetic field so when the armature spins, it generates output voltage (Physics 202, E & M ) generators, have permanent magnets so they don't need a battery (to supply field producing current), my old british bike could use a battery eliminator for that reason, if you could kick the engine over, ...

oh, ... the answer is: VOM won't test if alt is good in a junk yard except to test continuity of windings.

[Brant]

not the alternator.....
I want to test the small silver regulator that can be removed from the regulator panel...

anyway to test one of those in a junk yard, before I buy it?

brant

[Zeke]

Probably not. I'm sure you need some varialbe current to check it out. At the relativily low prices of a reg, why would you buy used one? I've even found alts rebuilt for under $70+ core which is $30 cheaper than Pelican. However, as always, if you get it from Pelican, you know where it came from. They probably sold some cheaper ones at one time and it didn't work out. But the regs are only $20 something brand new.

[Brant]

ok,

what should I look for to test them on a running car...
say that I get my car up and running (some day)...
and plug in unknown units....

is there going to be a spike (unregulated) at the battery terminals for a bad one...
or is there going to be a drop at the battery terminals for a bad one....

(would measuring at the battery terminals even be the best place?)

I've bought new ones before that were junk.
I have a bunch of used ones, I'd like to check out.

tia
brant

[914GT]

I think it's a little difficult to immediately tell what's going on inside the regulator in a running car. Given enough time you'll know you have a reg. problem if the battery constantly overcharges or it gradually discharges. But that's also assuming you know you have a good battery, alternator, and wiring in the charging system. A properly functioning regulator should likely be 'chattering' once the battery is charged up. Doubt if you could hear this with the motor running (especially in a 914). It's probably not impossible to check it directly but might mean disconnecting D+ and DF wires individually at the regulator somehow.
It should be possible to check it off the car with a DC power supply of at least 14 volts or so and a continuity light or meter. With no voltage (nothing) hooked up there should be continuity between DF and D+ (wants to charge). With >14 volts across D+ and D-, there should be continuity between DF and D- (no charging). At least this tells if the internal contacts and relay coil are good.

[Dave at Pelican Parts]

If you have a running 914 with a known good alternator, you can plug in the regulator and check the voltage across the battery terminals when the engine is running. If it reads between 13.5V and 14.5V, particularly over ~2000 RPM, you know the regulator is good. If it sits at 12.6V, or if it spikes to 16V or higher, the regulator is bad. Values out of the listed ranges would be marginal.

--DD