 Alternator light on? |
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| 914Toy |
 May 30 2020, 01:19 PM
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#1
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Senior Member  Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California 
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My alternator light comes on with ignition on, and stays on with engine running, and voltage stays at 12V regardless of rpm's. Was charging regularly at nearly 14V. The fan belt is in good order at spec tension. The alternator was reconditioned a couple of years ago and now has about 5,000 miles on it. The diode behind the gauge was also replaced, but I have had the gauge in and out a few times working on other issues - possibly damaging it(?)
Before removing the alternator for testing, could the diode behind the gauge be faulty preventing charging? If so, what is the spec of these diodes? Your suggestions will be welcome. |
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| dr914@autoatlanta.com |
May 30 2020, 02:12 PM
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#2
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914 Guru Group: Members Posts: 7,806 Joined: 3-January 07 From: atlanta georgia Member No.: 7,418 Region Association: None |
pull the regulator and make sure that the light goes out. If it does plug in a new voltage regulator (probably not that) so if the belt is tight the alternator has a problem
QUOTE(914Toy @ May 30 2020, 12:19 PM)  My alternator light comes on with ignition on, and stays on with engine running, and voltage stays at 12V regardless of rpm's. Was charging regularly at nearly 14V. The fan belt is in good order at spec tension. The alternator was reconditioned a couple of years ago and now has about 5,000 miles on it. The diode behind the gauge was also replaced, but I have had the gauge in and out a few times working on other issues - possibly damaging it(?) Before removing the alternator for testing, could the diode behind the gauge be faulty preventing charging? If so, what is the spec of these diodes? Your suggestions will be welcome. |
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| 914Toy |
May 30 2020, 03:38 PM
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#3
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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QUOTE(dr914@autoatlanta.com @ May 30 2020, 01:12 PM) pull the regulator and make sure that the light goes out. If it does plug in a new voltage regulator (probably not that) so if the belt is tight the alternator has a problem QUOTE(914Toy @ May 30 2020, 12:19 PM) My alternator light comes on with ignition on, and stays on with engine running, and voltage stays at 12V regardless of rpm's. Was charging regularly at nearly 14V. The fan belt is in good order at spec tension. The alternator was reconditioned a couple of years ago and now has about 5,000 miles on it. The diode behind the gauge was also replaced, but I have had the gauge in and out a few times working on other issues - possibly damaging it(?) Before removing the alternator for testing, could the diode behind the gauge be faulty preventing charging? If so, what is the spec of these diodes? Your suggestions will be welcome. Thanks for your comments. I have a hatch in the firewall, so will be removing the alternator for replacing the built in voltage regulator. |
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| Mikey914 |
May 30 2020, 03:51 PM
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#4
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The rubber man Group: Members Posts: 12,638 Joined: 27-December 04 From: Hillsboro, OR Member No.: 3,348 Region Association: None
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If you replaced your alternator light with a LED. The problem is the LED.
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| 73-914 |
May 30 2020, 05:11 PM
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#5
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Senior Member Group: Members Posts: 564 Joined: 24-April 10 From: Albany UpstateNY Member No.: 11,651 Region Association: None
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QUOTE(914Toy @ May 30 2020, 05:38 PM) QUOTE(dr914@autoatlanta.com @ May 30 2020, 01:12 PM) pull the regulator and make sure that the light goes out. If it does plug in a new voltage regulator (probably not that) so if the belt is tight the alternator has a problem QUOTE(914Toy @ May 30 2020, 12:19 PM) My alternator light comes on with ignition on, and stays on with engine running, and voltage stays at 12V regardless of rpm's. Was charging regularly at nearly 14V. The fan belt is in good order at spec tension. The alternator was reconditioned a couple of years ago and now has about 5,000 miles on it. The diode behind the gauge was also replaced, but I have had the gauge in and out a few times working on other issues - possibly damaging it(?) Before removing the alternator for testing, could the diode behind the gauge be faulty preventing charging? If so, what is the spec of these diodes? Your suggestions will be welcome. Thanks for your comments. I have a hatch in the firewall, so will be removing the alternator for replacing the built in voltage regulator. the voltage regulator is on the relay board not on the alternator |
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| ndfrigi |
May 30 2020, 05:22 PM
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#6
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Advanced Member Group: Members Posts: 2,925 Joined: 21-August 11 From: Orange County Member No.: 13,474 Region Association: Southern California
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QUOTE(73-914 @ May 30 2020, 04:11 PM) QUOTE(914Toy @ May 30 2020, 05:38 PM) QUOTE(dr914@autoatlanta.com @ May 30 2020, 01:12 PM) pull the regulator and make sure that the light goes out. If it does plug in a new voltage regulator (probably not that) so if the belt is tight the alternator has a problem QUOTE(914Toy @ May 30 2020, 12:19 PM) My alternator light comes on with ignition on, and stays on with engine running, and voltage stays at 12V regardless of rpm's. Was charging regularly at nearly 14V. The fan belt is in good order at spec tension. The alternator was reconditioned a couple of years ago and now has about 5,000 miles on it. The diode behind the gauge was also replaced, but I have had the gauge in and out a few times working on other issues - possibly damaging it(?) Before removing the alternator for testing, could the diode behind the gauge be faulty preventing charging? If so, what is the spec of these diodes? Your suggestions will be welcome. Thanks for your comments. I have a hatch in the firewall, so will be removing the alternator for replacing the built in voltage regulator. the voltage regulator is on the relay board not on the alternator Keith’s car is a 6 conversion |
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| Steve |
May 30 2020, 06:09 PM
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#7
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914 Guru Group: Members Posts: 5,564 Joined: 14-June 03 From: Orange County, CA Member No.: 822 Region Association: Southern California
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It's a 2.7 six. The alternator has a built in regulator. He is using a standard alternator light, not an LED.
Reading the manual... One side of the light goes to D+ on the regulator (blue wire) and the other side of the light goes to ignition + (RD/BK wire). If the light is on, it's getting power. Slight chance the blue wire is grounding, which will also enable the light. Can you get to the blue wire directly on the alternator and put a light on it and see if it makes a difference? Otherwise your going to have to pull the alternator again and get it tested. |
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| porschetub |
May 30 2020, 06:39 PM
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#8
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Advanced Member Group: Members Posts: 4,696 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(Mikey914 @ May 31 2020, 09:51 AM) If you replaced your alternator light with a LED. The problem is the LED. With an LED lamp it won't work from the get go,only the stock lamp will work for excitation of the altenator. Bugger when you have a built in VR as changing them is a bit of a chore with the six, not so bad with a firewall opening. |
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| Mark Henry |
May 30 2020, 07:07 PM
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#9
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
When I was building my engine there was enough cases of internal regulator failure that I went with a 70amp external regulator type.
But I also put in a huge hatch, so if I have to I can pull the fan in car. |
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| 914Toy |
May 30 2020, 07:49 PM
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#10
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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After checking the wiring behind the gauge, which looked OK, I spent the afternoon removing the alternator from the car via the firewall hatch. Will be ordering a new voltage regular tomorrow from PP. Expect to have it back together by Wednesday in time for the rally., (IMG:style_emoticons/default/driving.gif)
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| 914Toy |
May 31 2020, 08:06 AM
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#11
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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What is the purpose of the diode attached to the alternator light terminal. The Haynes manual shows it connected in parallel with the blue alternator wire, connected to the brown with white stripe wires, but detail is difficult to be sure?
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| Spoke |
May 31 2020, 08:47 AM
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#12
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Jerry Group: Members Posts: 6,971 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None
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QUOTE(914Toy @ May 31 2020, 10:06 AM) What is the purpose of the diode attached to the alternator light terminal. The Haynes manual shows it connected in parallel with the blue alternator wire, connected to the brown with white stripe wires, but detail is difficult to be sure? Keith, Can you show a picture of the schematic you refer to? I have an '86 930 and it doesn't show the diode you're referring to. There shouldn't be a diode in series with the GEN light as the current in the GEN light needs to be able to go both directions. Please post the schematic and/or my email: spokester@yahoo.com. BTW, while your alternator is out it might be worthwhile to have it tested if possible. |
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| Spoke |
May 31 2020, 09:00 AM
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#13
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Jerry Group: Members Posts: 6,971 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None
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QUOTE(914Toy @ May 30 2020, 03:19 PM) ...could the diode behind the gauge be faulty preventing charging? Below I'm showing the simplified schematic for the 914/4 charging system. The 911 charging system is very similar except the VR is located with the alternator. Notice there is no diode to speak of. Not sure what the diode on your gauge is for. Not sure even what the gauge has to do with the charging system except to hold the GEN light.  |
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| Mikey914 |
May 31 2020, 09:28 AM
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#14
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The rubber man Group: Members Posts: 12,638 Joined: 27-December 04 From: Hillsboro, OR Member No.: 3,348 Region Association: None
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That's why I thought he had put a diode in the indicator light position.
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| 914Toy |
May 31 2020, 10:40 AM
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#15
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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QUOTE(Spoke @ May 31 2020, 08:00 AM) QUOTE(914Toy @ May 30 2020, 03:19 PM) ...could the diode behind the gauge be faulty preventing charging? Below I'm showing the simplified schematic for the 914/4 charging system. The 911 charging system is very similar except the VR is located with the alternator. Notice there is no diode to speak of. Not sure what the diode on your gauge is for. Not sure even what the gauge has to do with the charging system except to hold the GEN light. This diagram is very clear thanks. I am removing this diode from behind the gauge, and ordering a new voltage regulator which I expect will solve the problem. Thanks Jerry. |
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| Mikey914 |
May 31 2020, 11:25 AM
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#16
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The rubber man Group: Members Posts: 12,638 Joined: 27-December 04 From: Hillsboro, OR Member No.: 3,348 Region Association: None
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removing the diode alone should make it work
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| Mark Henry |
May 31 2020, 12:10 PM
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#17
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Also some alternators have two B+, two D+ and two D- terminals, don't try to pair these extra terminals up, just pick one of each.
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| 914Toy |
Jun 2 2020, 07:15 PM
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#18
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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I have replaced the voltage regulator with a new one from PP on my 2.7 L 911 engine. After a light sanding clean of the two slip rings to mate with he voltage regulator carbon brushes, I installed the new regulator back onto the alternator. I started the engine and reved it up to about 2000 rpm - unfortunately - still no charge, with the warning light remaining on red and the voltmeter showing slightly over 12V - the battery voltage. The regulator is the $100 Valeo 5 star rated unit on PP which they say is the same as Porsche uses, but it is made in China (?).
After looking at a few "how to trouble shoot Alternators" videos, and checking all connections and correct attachment of the three wires to the alternator, I have to conclude that the alternator has failed. Subject to any further advice from this brain trust I plan to remove the alternator again tomorrow and take it for a professional checking. |
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| 914Toy |
Jun 3 2020, 03:10 PM
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#19
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Senior Member Group: Members Posts: 715 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California
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had the Alternator checked this morning. Not charging because on or more of the diodes had failed. Expect to pick up the alternator tomorrow morning and have it back in the car by the end of the day. So I expect to join all of you on Saturday morning early (IMG:style_emoticons/default/driving.gif)
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| porschetub |
Jun 3 2020, 05:57 PM
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#20
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Advanced Member Group: Members Posts: 4,696 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(914Toy @ Jun 4 2020, 09:10 AM) had the Alternator checked this morning. Not charging because on or more of the diodes had failed. Expect to pick up the alternator tomorrow morning and have it back in the car by the end of the day. So I expect to join all of you on Saturday morning early (IMG:style_emoticons/default/driving.gif) Good result Keith,can be frustrating sorting issues with charging systems (IMG:style_emoticons/default/headbang.gif) ,my Bosch 55a unit has kinda has been a PITA after being full rebuilt,NOS Bosch regulator and rebuilt relayboard added later have helped somewhat but don't think these old units play well with AGM battteries at its max charge under load is around 13.5V but it still appears to be working when it needs to (IMG:style_emoticons/default/biggrin.gif) . |
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