alternator mechanic cant tell me why, maybe one of you knows...
06-30-2014, 08:26 AM
#1
Drifting
Thread Starter
Member Since: Dec 2007
Location: Sumter South Carolina
Posts: 1,661
Likes: 0
Received 7 Likes
on
7 Posts
alternator mechanic cant tell me why, maybe one of you knows...
1989 - So not even the guy who owns his own alternator/starter/battery shop can give me an answer on why the hell gm is so redundant on its wiring to the alternator?
There is a 12ga red wire off the main terminal goes to fusable link/positive junction. Then off the pig tail comes another 12ga red wire that goes to the same place! Exactly the same! Then a blue wire that is 12v positive that comes from fuse box (then the brown -volt meter which could be taken anywhere on the frickin car, no need to run a wire all the way to the alternator) this is all factory wiring and the fsm varifys it.
Did gm make some deal with the copper industry to try to use as many wires as possible in these cars? My fsm says there are 899 wires!
The alternator guy sid cut the red pigtail, its useless, and wire the blue straight in line and the brown is just whatever.
This is just one instance ive found of prob 20 as ive rewired this car and I cant wrap my brain around it.
There is a 12ga red wire off the main terminal goes to fusable link/positive junction. Then off the pig tail comes another 12ga red wire that goes to the same place! Exactly the same! Then a blue wire that is 12v positive that comes from fuse box (then the brown -volt meter which could be taken anywhere on the frickin car, no need to run a wire all the way to the alternator) this is all factory wiring and the fsm varifys it.
Did gm make some deal with the copper industry to try to use as many wires as possible in these cars? My fsm says there are 899 wires!
The alternator guy sid cut the red pigtail, its useless, and wire the blue straight in line and the brown is just whatever.
This is just one instance ive found of prob 20 as ive rewired this car and I cant wrap my brain around it.
06-30-2014, 09:20 AM
#3
Instructor
It's been a while since I looked at the alternator schematics, but as I recall the red wire from the pigtail to the output is the "sense" line for the voltage regulator.
06-30-2014, 09:25 AM
#4
Wiring makes me sick!!!
BAN WIRING!!!!!!!!!!!!!!!!
Btw, I loled when I read "Exactly the same!"
..I feel your pain
The last few times I worked on my car (like today) I almost googled "C4 Corvette engineers" to find out who they were and then "local voodoo man witch curse" to get him/her to put a curse on them.
BAN WIRING!!!!!!!!!!!!!!!!
Btw, I loled when I read "Exactly the same!"
..I feel your pain
The last few times I worked on my car (like today) I almost googled "C4 Corvette engineers" to find out who they were and then "local voodoo man witch curse" to get him/her to put a curse on them.
06-30-2014, 10:31 AM
#5
1989 - So not even the guy who owns his own alternator/starter/battery shop can give me an answer on why the hell gm is so redundant on its wiring to the alternator?
There is a 12ga red wire off the main terminal goes to fusable link/positive junction. Then off the pig tail comes another 12ga red wire that goes to the same place! Exactly the same! Then a blue wire that is 12v positive that comes from fuse box (then the brown -volt meter which could be taken anywhere on the frickin car, no need to run a wire all the way to the alternator) this is all factory wiring and the fsm varifys it.
Did gm make some deal with the copper industry to try to use as many wires as possible in these cars? My fsm says there are 899 wires!
The alternator guy sid cut the red pigtail, its useless, and wire the blue straight in line and the brown is just whatever.
This is just one instance ive found of prob 20 as ive rewired this car and I cant wrap my brain around it.
There is a 12ga red wire off the main terminal goes to fusable link/positive junction. Then off the pig tail comes another 12ga red wire that goes to the same place! Exactly the same! Then a blue wire that is 12v positive that comes from fuse box (then the brown -volt meter which could be taken anywhere on the frickin car, no need to run a wire all the way to the alternator) this is all factory wiring and the fsm varifys it.
Did gm make some deal with the copper industry to try to use as many wires as possible in these cars? My fsm says there are 899 wires!
The alternator guy sid cut the red pigtail, its useless, and wire the blue straight in line and the brown is just whatever.
This is just one instance ive found of prob 20 as ive rewired this car and I cant wrap my brain around it.
Can it be eliminated in earlier cars? Certainly. A wise decision? Maybe NOT.
If you've done this change (difficult to determine from your comments) I'd think that you maybe have charging issues at low RPM. You didn't mention your alternator model or out-put so it's difficult to comment further. If it's an OE of the period alternator then I'd think it wise to use the connection type and "sensing" as engineered.
One-wire requires normally over 1000 RPM to excite and sometimes "way more". That would depend on manufacturer and model. Even PowerMaster and others still use the OE configuration for replacement alternators. If you want a one-wire from them you need to ask and they'll provide the wiring demands for that specific install.
Last edited by WVZR-1; 06-30-2014 at 10:52 AM.
06-30-2014, 11:47 AM
#6
Drifting
Thread Starter
Member Since: Dec 2007
Location: Sumter South Carolina
Posts: 1,661
Likes: 0
Received 7 Likes
on
7 Posts
I get that the regulator needs to sense voltage. What I dont get is why it cant tap into the main charging wire. Both wires go to the same place so its not like anything would be different. It would just eliminate a wire. Right now I have the blue, from what I can gather, is the "sensing wire" tapped straight into one of the fusable links.
I get what you mean with one wire alt. This would be a 2 wire if wired how the alt guy said to do it. The fsm says how it should be wired from the factory but it doesnt explain the inner workings of the alternator.
I just dont understand why two 12v wires go to the same place and are 4ft long when one wire split at the end would do the same thing. I understand the blue is an ignition thing so alt cant charge with key off.
I get what you mean with one wire alt. This would be a 2 wire if wired how the alt guy said to do it. The fsm says how it should be wired from the factory but it doesnt explain the inner workings of the alternator.
I just dont understand why two 12v wires go to the same place and are 4ft long when one wire split at the end would do the same thing. I understand the blue is an ignition thing so alt cant charge with key off.
06-30-2014, 02:53 PM
#7
Melting Slicks
Member Since: Aug 1999
Location: Baltimore, MD USA
Posts: 2,240
Likes: 0
Received 34 Likes
on
30 Posts
The Sense wire is 12 awg.
The Brown wire allows the alternator regulator to control the Charge indicator Lamp.
The dash cluster voltmeter monitors the Cluster fuse.
GM decided the critical voltage for the cars electrical system is at the Battery Jumper Block. So the Sense wire is at that location.
If you jump the Sense wire direct to the Bat. output terminal of the alternator, you're not compensating for the voltage drop that occurs because of the resistance of the wires and the electrical load in this case at the Battery Jumper Block.
06-30-2014, 02:55 PM
#8
I get that the regulator needs to sense voltage. What I dont get is why it cant tap into the main charging wire. Both wires go to the same place so its not like anything would be different. It would just eliminate a wire. Right now I have the blue, from what I can gather, is the "sensing wire" tapped straight into one of the fusable links.
I get what you mean with one wire alt. This would be a 2 wire if wired how the alt guy said to do it. The fsm says how it should be wired from the factory but it doesnt explain the inner workings of the alternator.
I just dont understand why two 12v wires go to the same place and are 4ft long when one wire split at the end would do the same thing. I understand the blue is an ignition thing so alt cant charge with key off.
I get what you mean with one wire alt. This would be a 2 wire if wired how the alt guy said to do it. The fsm says how it should be wired from the factory but it doesnt explain the inner workings of the alternator.
I just dont understand why two 12v wires go to the same place and are 4ft long when one wire split at the end would do the same thing. I understand the blue is an ignition thing so alt cant charge with key off.
Midway through this link the wiring concepts are maybe explained well enough that it might help you understand. You need to bear with the early portions of the explanation but it gets better. It's also based primarily on the CS130 found on the early cars. It's a good read for sure:
http://www.pirate4x4.com/tech/billavista/Wiring/Part2/
07-01-2014, 11:36 PM
#9
Instructor
Member Since: Apr 2013
Location: NW Arkansas - usually winter in FL
Posts: 144
Likes: 0
Received 0 Likes
on
0 Posts
Hi rithsleeper -
WVZR and Hooked are spot on regarding this. I worked for the competition but I can say this - GM engineers are not stupid. Somewhere there is a reason for what they have done. It may well be something which is easily not diagnosed or understood by the service industry, like RFI/EMI.
Then again, old engineers get set in their ways - "We do it that way because that's the way we've always done it". LOL!
If it were me, I'd do what the factory guys did. As noted by the folks above, there might be more to this than meets the eye. WVZR and Hooked seem to know what they are talking about - way more than me. I'd take their advice under serious consideration.
Would what you suggest work? Yeah, I think it would but one would not be utilizing the full potential of the charging system. Low output at low engine speeds and perhaps some poor voltage control across the entire spectrum. Flickering headlamps even under cruise conditions because of the voltage variations and total charging system maximum output might be sacrificed a little as well. A non-gearhead might be oblivious to this, but I think you will be able to recognized the differences.
Remember the ground side too because what the alternator puts out must return through the ground paths. Be positive that all ground straps are in place because on older cars which have been tinkered with, sometimes the straps get left off or not "reconnected".
As per usual, just my thoughts. Sorry for the rant - LOL
Best -
Jake -
WVZR and Hooked are spot on regarding this. I worked for the competition but I can say this - GM engineers are not stupid. Somewhere there is a reason for what they have done. It may well be something which is easily not diagnosed or understood by the service industry, like RFI/EMI.
Then again, old engineers get set in their ways - "We do it that way because that's the way we've always done it". LOL!
If it were me, I'd do what the factory guys did. As noted by the folks above, there might be more to this than meets the eye. WVZR and Hooked seem to know what they are talking about - way more than me. I'd take their advice under serious consideration.
Would what you suggest work? Yeah, I think it would but one would not be utilizing the full potential of the charging system. Low output at low engine speeds and perhaps some poor voltage control across the entire spectrum. Flickering headlamps even under cruise conditions because of the voltage variations and total charging system maximum output might be sacrificed a little as well. A non-gearhead might be oblivious to this, but I think you will be able to recognized the differences.
Remember the ground side too because what the alternator puts out must return through the ground paths. Be positive that all ground straps are in place because on older cars which have been tinkered with, sometimes the straps get left off or not "reconnected".
As per usual, just my thoughts. Sorry for the rant - LOL
Best -
Jake -
Last edited by jake corvette; 07-02-2014 at 12:49 AM. Reason: info