1979: Parasitic draw and zilch from the alternator... - Rennlist - Porsche Discussion Forums

Go Back  Rennlist - Porsche Discussion Forums > Water Cooled Technical Discussion Areas > 928 Forum
Reload this Page >

1979: Parasitic draw and zilch from the alternator...

Notices
928 Forum
Sponsored by:
Sponsored by: 928 Specialists

1979: Parasitic draw and zilch from the alternator...

 
Old 12-17-2018, 10:44 AM
  #1  
Blackdog2
User
Thread Starter
 
Blackdog2's Avatar
 
Join Date: Oct 2018
Location: Maine
Posts: 12
Default 1979: Parasitic draw and zilch from the alternator...

Following up from This Thread...

I have pulled every fuse and every relay with my DVM connected between the battery and ground strap and I'm still showing an almost 4 volt draw! (all doors and hood closed) Not sure where to go next. also, with the DVM on the battery (fully charged) I get 12.75v and there is no change when rpms are increased this will slowly drop obviously as no charging is taking place.... I'm wondering if there's something wrong in the alt and that might be whats pulling the amperage? I've checked all the easy stuff... loose belts and wires.....

thanks for any help or suggestions....

Last edited by Blackdog2; 12-17-2018 at 01:17 PM. Reason: fixed my screw up.... it's 4 volts, not mA
Blackdog2 is offline  
Old 12-17-2018, 01:04 PM
  #2  
dr bob
Chronic Tool Dropper
Lifetime Rennlist
Member
 
dr bob's Avatar
 
Join Date: Oct 2001
Location: Bend, Oregon
Posts: 17,492
Default

What kind of car are you working on?


Later 928 cars typically draw 30+mA at rest, for things like engine management memory, plus radio keep-alive, clock, etc. Some cars draw a little more when the doors are closed and locked, for the alarm system. If you happen to leave the key in the ignition, even in the 0 (off) position, there's a small extra drain from that circuit too.

Aftermarket audio, alarm, or the remains of a period cellphone install? All are candidates for parasitic drain.

A lot depends on what year your car is, what accessories are installed, and what's active for the 'current' state.


The alternator charging may or may not be related to the drain. You can isolate the alternator by disconnecting the feeds from the starter solenoid stud (from the battery), and the connection from the engine harness side of the jump post connections at the right forward fenderwall under the hood. Alternators that suffer from failed (shorted) diodes will usually draw a lot more than 4mA. Add back a separate temporary jumper wire from the starter positive post to the jump post on under the hood.

-------
Welcome to Rennlist!

Invest the few dollars in a paid membership. One of the many benefits is the ability to build a "signature" section that's appended to the end of every post. In that section you can put the details of the car(s) you are working on. It saves you the work of having to type that info into every post manually. We deal with forum participants who own cars from he full range of production years. Many are working on several cars at the same time so still get to remind us what they are working on. There's a wide variation in electrical loads and drains depending on the year and sometimes the market into which the car was originally sold. For instance.

Your intro thread includes some serious front-of-engine (KS2) wiring harness damage. The connector end you show is likely the best part of the harness. You might short-cut your drain-chasing some by replacing that harness now, You'll be doing it before you drive the car much anyway. The harness includes the excitation trigger to the alternator, critical to getting it to charge. That circuit includes the "charge" light in the cluster, paralleled with a resistor. If your charge light doesn't come on with key on (position 2 "engine run") but with engine not running, there's a break in that excitation circuit.

You can buy replacement harnesses from any of several sources, including our trusted sponsor vendors 928 International, 928SRUS, Greg Brown, or 928 Motorsports. You can get a replacement that looks and feels like original, or one that includes modern heat shielding. All use modern wire insulation that's more heat and chemical resistant. Some offer wire upgrades to the primary power feed conductors between the starter, alternator, and the jump post.
dr bob is offline  
Old 12-17-2018, 03:53 PM
  #3  
Blackdog2
User
Thread Starter
 
Blackdog2's Avatar
 
Join Date: Oct 2018
Location: Maine
Posts: 12
Default

Originally Posted by dr bob View Post
What kind of car are you working on?


Later 928 cars typically draw 30+mA at rest, for things like engine management memory, plus radio keep-alive, clock, etc. Some cars draw a little more when the doors are closed and locked, for the alarm system. If you happen to leave the key in the ignition, even in the 0 (off) position, there's a small extra drain from that circuit too.

Aftermarket audio, alarm, or the remains of a period cellphone install? All are candidates for parasitic drain.

A lot depends on what year your car is, what accessories are installed, and what's active for the 'current' state.


The alternator charging may or may not be related to the drain. You can isolate the alternator by disconnecting the feeds from the starter solenoid stud (from the battery), and the connection from the engine harness side of the jump post connections at the right forward fenderwall under the hood. Alternators that suffer from failed (shorted) diodes will usually draw a lot more than 4mA. Add back a separate temporary jumper wire from the starter positive post to the jump post on under the hood.

-------
Welcome to Rennlist!

Invest the few dollars in a paid membership. One of the many benefits is the ability to build a "signature" section that's appended to the end of every post. In that section you can put the details of the car(s) you are working on. It saves you the work of having to type that info into every post manually. We deal with forum participants who own cars from he full range of production years. Many are working on several cars at the same time so still get to remind us what they are working on. There's a wide variation in electrical loads and drains depending on the year and sometimes the market into which the car was originally sold. For instance.

Your intro thread includes some serious front-of-engine (KS2) wiring harness damage. The connector end you show is likely the best part of the harness. You might short-cut your drain-chasing some by replacing that harness now, You'll be doing it before you drive the car much anyway. The harness includes the excitation trigger to the alternator, critical to getting it to charge. That circuit includes the "charge" light in the cluster, paralleled with a resistor. If your charge light doesn't come on with key on (position 2 "engine run") but with engine not running, there's a break in that excitation circuit.

You can buy replacement harnesses from any of several sources, including our trusted sponsor vendors 928 International, 928SRUS, Greg Brown, or 928 Motorsports. You can get a replacement that looks and feels like original, or one that includes modern heat shielding. All use modern wire insulation that's more heat and chemical resistant. Some offer wire upgrades to the primary power feed conductors between the starter, alternator, and the jump post.
Thanks, and thanks for linking the threads....it is, as you figured out, a 79. is this what you're talking about? I agree, the wires from the 14 pin connector do not look good....

https://928motorsports.com/parts/wiringharness.php



Blackdog2 is offline  
Old 12-17-2018, 07:59 PM
  #4  
dr bob
Chronic Tool Dropper
Lifetime Rennlist
Member
 
dr bob's Avatar
 
Join Date: Oct 2001
Location: Bend, Oregon
Posts: 17,492
Default

That one, or better yet get one from Roger or Greg. The ones from Roger or Greg have all new connectors, plus options for upgraded primary conductors and wrappings. The connectors are critical too. If your future includes things like additional electric fans, better lighting, and/or audio system improvements, any additional alternator capacity immediately needs bigger primary conductors in that harness. Any of the good replacements will suit your stock needs. A little searching here will net you some pics and descriptions.

---

A little sleuthing lead me to your earlier thread and pictures, so it was pretty painless to add the link and update the title once I had the right info.

For those playing along at home, you can always edit the thread title yourself if you are the thread starter. Just open your first post to edit, and select the 'advanced' option. Edit the thread and title as needed, then 'save' the changes. You may need to refresh your browser cache (F5 in Wndows) to see the changes.
dr bob is offline  
Old 12-18-2018, 02:00 PM
  #5  
Blackdog2
User
Thread Starter
 
Blackdog2's Avatar
 
Join Date: Oct 2018
Location: Maine
Posts: 12
Default

Originally Posted by dr bob View Post
That one, or better yet get one from Roger or Greg. The ones from Roger or Greg have all new connectors, plus options for upgraded primary conductors and wrappings. The connectors are critical too. If your future includes things like additional electric fans, better lighting, and/or audio system improvements, any additional alternator capacity immediately needs bigger primary conductors in that harness. Any of the good replacements will suit your stock needs. A little searching here will net you some pics and descriptions.

---

A little sleuthing lead me to your earlier thread and pictures, so it was pretty painless to add the link and update the title once I had the right info.

For those playing along at home, you can always edit the thread title yourself if you are the thread starter. Just open your first post to edit, and select the 'advanced' option. Edit the thread and title as needed, then 'save' the changes. You may need to refresh your browser cache (F5 in Wndows) to see the changes.
who are Roger and Greg?
Blackdog2 is offline  
Old 12-18-2018, 04:17 PM
  #6  
docmirror
Shameful Thread Killer
Rennlist Member
 
docmirror's Avatar
 
Join Date: Aug 2004
Location: Rep of Texas, N NM, Rockies, SoCal
Posts: 19,380
Default

Go to 928sRUS.com, Roger's contact info will be there, and he can direct you to Sean who makes the new harness.
docmirror is offline  
Old 12-18-2018, 05:52 PM
  #7  
Blackdog2
User
Thread Starter
 
Blackdog2's Avatar
 
Join Date: Oct 2018
Location: Maine
Posts: 12
Default

Originally Posted by docmirror View Post
Go to 928sRUS.com, Roger's contact info will be there, and he can direct you to Sean who makes the new harness.

Thanks!
Blackdog2 is offline  
Old 12-19-2018, 08:55 PM
  #8  
Wisconsin Joe
Super User
 
Wisconsin Joe's Avatar
 
Join Date: Jan 2013
Location: Kaukauna Wisconsin
Posts: 4,279
Default

Roger is Roger Tyson, "Parts Supplier Extraordinaire". ROG100 on here.

Somehow, a transplanted Brit ended up in DFW Texas, selling German car parts. He knows & loves these cars as much as anyone on here, even the one he started on fire.
He supplies parts to owners all over the world. He knows the cars and the parts well enough that many of us simply tell him what job we are doing (TB/WP, Intake refresh, ect) and say "send what I need". Really.
He only sells good parts and stands behind what he sells (no cheap knockoffs).
His site is rather sparse, however. When you need something, call on the phone and actually talk to him (always a very pleasant chat with a nice fella) or e-mail.

Greg is "Doc" Greg Brown. Probably the top 928 wrench in the world. He makes a variety of upgraded replacement parts for the car. "GB" fuel lines are top of the line. His oil baffle is the best on the market.
His shop, Precision Motorwerks is always full of 928s. He's booked up a long way in advance (that should say something).
He also makes custom stroker motors. Works of art. Not cheap, but worth every penny. He also rebuilds both auto and manual transmissions.
Wisconsin Joe is online now  
 


Thread Tools
Search this Thread

Contact Us About Us Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: