Charging system puzzle on the V8, A leaker sneaks back in with a Q Options

[aircooledboy]

Hey Everybody. (IMG:style_emoticons/default/bye1.gif) Mind if I sneak back into the clubhouse? (IMG:style_emoticons/default/wub.gif)

Been buried under life's relentless realities for the last 18 months or so, and 914s were by necessity out of the picture for a while. It feels good to be back and see many of the same standby names still active here.

The clouds have parted a bit, and I dusted off the 8 a couple weeks ago only to remember it had a charging problem when I parked it. I turn a wrench pretty well, but electrical issues make my brain hurt. (IMG:style_emoticons/default/confused24.gif) I'm hoping somebody can offer some ideas.

The car has had charging issues since I bought it. Now that I have had the alternator rebuilt for the third time in 5 years, I'm pretty sure that is a symptom and not a cause of the trouble. In trying to reason it through (unsuccessfully), I have noted or found the following:

1) Since the day I got the car, I noticed that when the turn signals are on, or when I step on the brakes (light the lamps), I could hear the fuel pump slow down accordingly. I always attributed that to a weak ground somewhere. Later I installed a volt meter in the car, and I see a temporary drop off of a volt or 2 when either of those things are things are on.

2) With the car off, if I check the voltage at the output pole of the alternator (or anywhere), the voltage is about 12.5. If I turn the key on, but don't start the car, the voltage at the alt. pole drops to 3-8 volts. (IMG:style_emoticons/default/wacko.gif) It stays 12.5ish anywhere else. When I start the car, the alt. output does not go up (fresh alt rebuild).

3) The alternator on the V8 only has one input, and that's the indicator light wire. If I disconnect that wire, the voltage doesn't drop at the output pole when I turn the key on. Key on, the voltage in the disconnected indicator wire is 12.5, but I have found that if I connect a test light to a hot, w/ key on, the indicator light wire will light the light (i.e. function as a ground also). Seems to me that points to a short, but I don't know. That's when my brain begins to ache. (IMG:style_emoticons/default/sad.gif)

4) I disconnected the main ground points under the dash and in the engine compartment for cleaning, and found that even with them both off, the dash cluster still functioned normally. (IMG:style_emoticons/default/huh.gif) My 3rd grader level ability to read a wiring diagram seems to say the cluster shouldn't work with those disconnected, but it did. More proof of a short?

John built a great car mechanically, but wiring looked not to be his forte. Under the dash is more than a little bit of a diy cluster fark, and starting over would be a serious effort. I'm hoping one of you guys can help me efficiently sort this out. Otherwise, she may get parked for another extended spell. That would bring me down.

[Mike Bellis]

I can tell you from experiance, the 914 has one of the poorest ground planes in a vehicle. This is evidenced by photos of floor pan replacements. Being 40 years old, the 914 only conducts ground through spot welds now. On my V8 car with the battery relocated to the front, I ran 2 gauge positive and negative cables back to the engine.

Due to high resistance in the vehicle ground plane, the body/chassis of the 914 acts like a load on the electrical system and not a simple conductor. Tru usung a #6 wire and connect all the ground pionts and carry the ground back to the battery and engine. This will improve the performance of the charing system.

[Tom]

In your original post, para #2, it sounds like your hot wire from alternator to ?. (in a stock car that goes to the starter and then on to the battery.) If yours goes there , check the voltage at alt output and then again at the starter where the alt wire connects, then at battery. They should all be near the same. If not, you have a failing connection. Sounds like the alt hot wire may be the culprit to me.
Also as Mike said, GROUNDS! The pain in the rear for these cars. Mike's solution make a LOT of sense.
Tom

[904svo]

Try this remove the battery lead lead from the alternator and check the voltage output, should be greater than 13.0 volts, if not the one wire lead my be wired wrong. Also some alternators do not but out voltage till after 1300 RPM"S some
times the alt pulley is changes to a smaller one this will also cause problems.
Some alternators do put out voltage at idle you have to check on these alternators
to find one that does if thats your problem.

[aircooledboy]

I can tell you from experiance, the 914 has one of the poorest ground planes in a vehicle. This is evidenced by photos of floor pan replacements. Being 40 years old, the 914 only conducts ground through spot welds now. On my V8 car with the battery relocated to the front, I ran 2 gauge positive and negative cables back to the engine.

Due to high resistance in the vehicle ground plane, the body/chassis of the 914 acts like a load on the electrical system and not a simple conductor. Tru usung a #6 wire and connect all the ground pionts and carry the ground back to the battery and engine. This will improve the performance of the charing system.

Thanks Mike.

I also have front a mounted battery with a #2 positive all the way back to engine, but the battery is grounded right in the front trunk. Do you think stringing the grounds together as you describe might solve my problem?

[aircooledboy]

Tom, my alt is wired the same as stock (i.e. output hot to starter to battery). The voltage drop when I turn the key on is only at the alt output pole. The voltage at the starter stays at 12.5-ish.

904, that might be the only thing I haven't checked. I assume it will be little or no voltage coming out if I remove the output wire, but I will check it.

[Mike Bellis]

Thanks Mike.

I also have front a mounted battery with a #2 positive all the way back to engine, but the battery is grounded right in the front trunk. Do you think stringing the grounds together as you describe might solve my problem?

I bonded my battery in the front and also ran a #2 ground back to the engine block. All my ground points are bonded with #6 back to the battery. I run a Power Master 70/120 alternator. 70 amps at idle and 120 amps above 1500 rpm. I also run a GM style EFI system so power and ground is very important. My electrical system works great! I have a 300W Rockford amp that runs without dimming the headlights.

The best thing we can do to improve our ground plane is seam welding. Seam welding is very time consuming and can also tweek and bend the car if not done correctly. Once the car is seam welded, all panels conduct ground with less resistance. Our big problem is the rust between panels that surrounds the spot welds. The ultimate would be acid dipping the shell and then seam welding with the car on a jig.

[Tom]

Only reason I can think of for a large wire like the alt. hot lead to loose so much voltage is a bad connection or a very high current draw at the alt. That kind of current draw at the alt signals a bad diode or filter cap. Is the alt. hot wire getting warm?
Tom

[aircooledboy]

Just back from one of the kids games, I went out to the shop.

I left the key on for 5 minutes, and niether wire to the alternator got warm at all. (I thought I would have noticed that, but double checked anyway).

Hy-evah, I also took the lead off the out put pole of the alt, and even though the input/indicator light lead is at 12.5, output was 3. (IMG:style_emoticons/default/mad.gif) When I installed the rebuilt alt tuesday, I thought it sounded a little funky for the first 10 seconds or so, but I decided it was my imagination after it quit. Maybe not. (IMG:style_emoticons/default/headbang.gif)

I still think I have other issues, but I need a working alt as step 1. Back to the rebuild shop in the morning she goes. Hmmmm.

[rick 918-S]

Sounds like two unrelated problems. The dipping of the alt and dimming of the lights when activating other accessories could mean anything from a corroded cable (either positive OR ground) to something incorrectly wired.


Here's a couple links for the alternator wiring. This may help a little. Wiring Sux. It's very rewarding when you get it right.

http://www.novaresource.org/alternator.htm

http://mightymo.org/Proj_OneWire.html

http://www.alternatorparts.com/FAQ.htm


Good to see you posting again Chris! (IMG:style_emoticons/default/bye1.gif)

BTW: you will have the best success with wiring if you set aside a couple days in the shop. I find if I have to walk away from the trouble shooting I end up having to start over.

[drive-ability]

hey if your output voltage at the alt is good with the key off, and low with the key on. Seeing its a one wire unit makes no sense to me. If it has only one wire it can't tell if the ignition is on or off, because its always on if that wire is hot as you say. That sounds like an error made in the measurement on your end. Sure it could be on the ground end but your just measuring voltage and a ground the size of a blade of grass will do in that case. You need someone who knows a bit more about auto electrical systems.. If it has two wires, output and sense then the alternator is likely faulty.. IMO Just rebuilt means not tested or proven to operate yet.

[aircooledboy]

hey if your output voltage at the alt is good with the key off, and low with the key on. Seeing its a one wire unit makes no sense to me. If it has only one wire it can't tell if the ignition is on or off, because its always on if that wire is hot as you say. That sounds like an error made in the measurement on your end. Sure it could be on the ground end but your just measuring voltage and a ground the size of a blade of grass will do in that case. You need someone who knows a bit more about auto electrical systems.. If it has two wires, output and sense then the alternator is likely faulty.. IMO Just rebuilt means not tested or proven to operate yet.

2 wires, bro. Like I said in my 1st post, 1 input from idiot light and 1 output.

As far as testing, I watched the builder spin it up, and while I didn't see the gauge, I assumed it read ok or he wouldn't have bothered to test it before he handed it to me. I guess I'll find out today.

[drive-ability]

If the output wire reads 3 volts when the ignition is on, that means a 12 volt feed connected directly to a battery source is being reduced / pulled way down not a good thing and would expect to see smoke or one heated circuit .

On the other hand the sense wire leading to the dash light should read with the ignition on very low around 3 volts.
I have a 200 amp unit on my V8 and it is a true one wire unit, no sense wire just a output circuit. Sorry for the confusion.

[aircooledboy]

No sweat, drive. Like I always say, never bitch about the way somebody trys to help you. Are you saying the sense lead should only show around 3 volts with the key on?

I just came from the builder, watched him test the alt, and saw it make 14.8 volts and 125 amps under load. (IMG:style_emoticons/default/dry.gif) The only possible conclusion is that there is something seriously hinky with the sense/idiot light wiring. Long term, I'm afraid that means rewiring the spagetti mess under the dash & the A/C to find the error. Short term I thought I might just bypass the idiot light and energize the alt with a "key on" lead straight to the alt, but if that lead is only supposed to be about 3 volts, I guess I shouldn't do that. (IMG:style_emoticons/default/confused24.gif)

Crap. Looks like the car cover might win again. (IMG:style_emoticons/default/mad.gif) The 914 time clock is winding down for 2010 here in the midwest. I'm not sure I can justfy the time investment of a rewire considering how soon the snow is prolly gonna fly 'round here.

[David_S]

I'm no alternator expert, and it has been a while since I have messed with a Chevy alternator, but there are a few things that dont add up in my mind !!! The only Chevy alternators that I have ever seen were either 1 wire or 3 wire. I have never seen a 2 wire Chevy alternator! If yours is a 1 wire, then it dont need the idiot light wire for it to charge. If yours is a 3 wire alternator, then it isnt charging because you have a wire missing. I can't remember what the terminals are labelled, but if you dont have a pigtail, you should be able to pick one up at your local FLAPS. The little wire in the pigtail should be the key on excite wire (battery voltage with the key on) and the bigger wire should have battery voltage all of the time. The 3rd wire should be the lead that goes back to the starter or battery. A quick fix that we do in the tractor world is to supply the small wire with keyed voltage, the bigger wire next to it just jumpers to the output (stud) terminal, and the stud terminal should go to the battery terminal on the starter. If this doesnt make sense, let me know and I will try to get you a diagram !!!

[David_S]

Damn double post!!!

[904svo]

The 1 wire lead for the GEN bulb should have 12 volts on it when the key is turn on
which comes from fuse #9. Check and make sure there is 12 volts on fuse #9 when the key is turn on. The gen lamp is a 2 wire socket Red/White on one and a Blue wire on the other which goes to the alternator thru the wiring harness.

[aircooledboy]

David, this was 3 wire, but only 1 of the 2 wires in the plug at the alt is used (the other has been cut at the plug).

My understanding has always been that the idiot light wire also provides the juice to excite the field (I figured the unused wire to the plug was for someting like a gauge that Renegade didn't include, so it was simply cut off the factory plug). I didn't wire this bad boy, and the Renagade installation manual that came with the car is pretty skinny on wiring details. Is it possible that I'm missing the wire needed to excite the field?

[David_S]

David, this was 3 wire, but only 1 of the 2 wires in the plug at the alt is used (the other has been cut at the plug).

My understanding has always been that the idiot light wire also provides the juice to excite the field (I figured the unused wire to the plug was for someting like a gauge that Renegade didn't include, so it was simply cut off the factory plug). I didn't wire this bad boy, and the Renagade installation manual that came with the car is pretty skinny on wiring details. Is it possible that I'm missing the wire needed to excite the field?

That's what it sounds like to me. See if you can somehow shove a jumper into the terminal that has been cut, and hook it to the stud, start the car, and see if it charges .... I would nearly bet that it will. I am looking right now for a good wiring diagram that might make it easier to understand.

[aircooledboy]

The 1 wire lead for the GEN bulb should have 12 volts on it when the key is turn on
which comes from fuse #9. Check and make sure there is 12 volts on fuse #9 when the key is turn on. The gen lamp is a 2 wire socket Red/White on one and a Blue wire on the other which goes to the alternator thru the wiring harness.

I will check the volts at #9 when I get home. I do know I had 12 at the plug end for that wire, but like I said, it also acted as a ground, so I'm not sure what the deal is with that wire. Unfortunately, the gauges have been nicely but significantly modified, which is where all the DIY wiring comes in. I can't chase a problem by starting with the color coded diagram, 'cause the wires ain't those colors no more.

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