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Discussion Starter #1
Hi all, I posted this in the scirocco forum, but cross-posted since that forum seems to be less active than this one, and the scirocco shares the same platform, engine, and electrical as the rabbit. Hope you can help!

I have a 1981 MK1 Scirocco with the 1.7L gasoline engine and bosch alternator w/ integrated/internal voltage regulator.

The main issue is that the alternator is only putting out 13V while the engine is running, not the 14.5V that it should, even though the alternator is newly refurbished. There is also some sort of parasitic drain on the battery while the car is turned off, approx. 1V loss per day (may or may not be related). Here are the readings and recent work:

  • Newly refurbished alternator. It was told it now puts out 14V+ and the integral voltage regulator was checked out and is good
  • brand new battery
  • engine running, alternator puts out 13V
  • 2 large prongs on the alternator connection test at 11.6V with the engine off
  • 1 small prong on the alternator connection tests at 11.6V when the key is turned
  • Alternator ground connection checks out good as well
Any thoughts? I covered the basics and what is described in the manual, and left confused.

Thanks!
 

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Moved your thread to the General forum, as this is the DIY forums.

The alternator will put out 13-85-14V when new.
Since running yours you are having less than that did you have it bench tested while you watched?

Parasitic drains may be the issue as well as the Ground cables or the main power cable to your alternator.
Did you clean your grounding points for the engine/Tranny and or the main frame grounding point?

The main grounds on your car are well over 40 years old, and probably need to be refreshed.
Proper grounding will only assist you and not hurt you. Cables as they get older are subject to road rash/salt/battery outgassing.
The OEM cable was unshielded and may look good, or are they a really ugly brown color?

Is there a ground wire from the Alternator Bracket to the engine block from a case nut?

Your ride was made in Germany so you should have the 2 studded alternator. That is one big stud for the B+ out and the itty-bitty one that has a blue wire attached.
This blue wire is the exciter that runs from the Battery to the Instrument cluster, and back to the alternator to tickle the alternator to start a field for the Alternator to generate power.

Out of hand I would also ask how you are measuring the voltage by the gauge in the car, or by using a DVOM on the battery. If you are using the gauge in the car, it is time that you test the battery with a Digital Volt Ohm Meter as I have a Cabriolet that is about 1 volt different than the actual. If the voltage on the Battery to frame is different than the console gauge, then you have found your problem bad wire or connection to the gauge or the gauge is bad.

The battery ground on the car run from the main negative post to the frame that should be under the CIS Dizzy, it is easier to get to from under the car than over it. From there it runs to your engine/tranny as they did more ground one them from one style to the other so it may be attached to the engine/tranny double studded where the bell housing connects to the block, or where the transmission hanger bolts to the transmission.

You should also have a ground wire from the Valve cover to the Coil bracket.

First test is Checking the battery fully charged with the leads off. Measure from the Positive lead to the negative and you should have 12.5V
Connect the Ground cable to the battery and measure from the Positive Post to any frame ground point NOT the ENGINE you should have the same voltage as you got from between posts. If not you have a bad cable. If the battery to frame is the same then check the Battery to the engine block, it too should be the same if not Bad cable.

Quick test is to take a set of battery jumper cables and connect them as this.
Red lead on the jumper from the battery negative to any good frame point, such as the Strut tower nuts.
Take the black cable and attach it to the negative side of the battery as well then to the Engine lifting ear. Now start the car and see what the voltage is on the battery, 13.8 to 14V issue solved. Bad Cables.

If you looked at the DIY section under Brianos Link by class Electrical there is a link to a video on Parasitic draws. When checking for them be sure you remove the courtesy light or turn it off when the doors are opened on the car as that can throw the tests out or burn out your meter. I have moved it as a sticky to the main sub section.

Here is the link.
or

Let us know how you get out, as we will help you nail this thing.

Most common causes of drains are improper installation or Sub Amps, After market Radios, Alarms....
 

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Discussion Starter #3
Hi, Thank you so much for your detailed reply! I have a bunch to check out now which I will do today or tomorrow! A few answers to your questions though in the meantime.

Since running yours you are having less than that did you have it bench tested while you watched? I didn't watch the bench test. The unit looked so band new again I didn't even question the guy!

Did you clean your grounding points for the engine/Tranny and or the main frame grounding point? Didn't clean the contacts or check this out. I'll do this as a double check.
The OEM cable was unshielded and may look good, or are they a really ugly brown color?
Is there a ground wire from the Alternator Bracket to the engine block from a case nut? Yes there is. It is unshielded and doesn't look in great shape (wires fraying). However, checking the ground connectivity from the alternator housing to the negative battery terminal checks out with 0.1V with the engine running. This was the procedure outlined in the manual but is there a different or better way to do this?

Out of hand I would also ask how you are measuring the voltage by the gauge in the car, or by using a DVOM on the battery. I used both an aftermarket installed voltage gauge in the car as well as a multimeter on the battery. Both have the same readings.

The battery ground on the car run from the main negative post to the frame that should be under the CIS Dizzy, it is easier to get to from under the car than over it. From there it runs to your engine/tranny as they did more ground one them from one style to the other so it may be attached to the engine/tranny double studded where the bell housing connects to the block, or where the transmission hanger bolts to the transmission. I will check this out.

You should also have a ground wire from the Valve cover to the Coil bracket. I will check this out.

First test is Checking the battery fully charged with the leads off. Measure from the Positive lead to the negative and you should have 12.5V. yes this is good!
Connect the Ground cable to the battery and measure from the Positive Post to any frame ground point NOT the ENGINE you should have the same voltage as you got from between posts. If not you have a bad cable. If the battery to frame is the same then check the Battery to the engine block, it too should be the same if not Bad cable. I will check this out

Quick test is to take a set of battery jumper cables and connect them as this.
Red lead on the jumper from the battery negative to any good frame point, such as the Strut tower nuts.
Take the black cable and attach it to the negative side of the battery as well then to the Engine lifting ear. Now start the car and see what the voltage is on the battery, 13.8 to 14V issue solved. Bad Cables. I will check this out

If you looked at the DIY section under Brianos Link by class Electrical there is a link to a video on Parasitic draws. When checking for them be sure you remove the courtesy light or turn it off when the doors are opened on the car as that can throw the tests out or burn out your meter. I have moved it as a sticky to the main sub section. I will check this out
 

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Not having it tested in front of you is accepting fate. I got 3 bad ones from napa in about 4 hours, the last one I had tested as well as the first 3 and they all tested bad save for the last one so one out of 4 off the shelf were bad, all had been rebuilt 10 years previous.
 

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handy voltmeter hack

Getting the alternator tested at an autozone or wherever is a must. Could be a just failing voltage regulator, get another online, stores don't want to sell you those.
As far as losing voltage- the battery could have a shorted cell in which case it will lose voltage while disconnected.
- alternator could have bad internal diodes

- car wiring shorts, solder wires to a 12v bulb and put it in-line between the +batt and the +cable terminal. If the bulb lights at all (ignition off) there is power going (leaking) somewhere - pull the fuses one at time and see if the light goes out and, if so, Track down that circuit - Ex.: there is power that goes to the dome light all the time, a switch on the light and door (buttons) that also turn on the dome light [middle position is off]. The horn also has power that goes to it all the time and is grounded by the button on the steering wheel.
The thing about mk1's is the wiring was a hack-job from the factory.
Sometimes the best thing is to just disconnect a circuit or run your own wiring is something is problematic.

Copper lugs are all you need for making custom larger wiring and ground cables, junkyard cables are cheap source for heavy gauge copper wire.

 

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Discussion Starter #6
Not having it tested in front of you is accepting fate. I got 3 bad ones from napa in about 4 hours, the last one I had tested as well as the first 3 and they all tested bad save for the last one so one out of 4 off the shelf were bad, all had been rebuilt 10 years previous.
Dang, yeah I am starting to question the refurb job but have some other tests to do first as recommened! Thanks!
 

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handy voltmeter hack

Getting the alternator tested at an autozone or wherever is a must. Could be a just failing voltage regulator, get another online, stores don't want to sell you those.
As far as losing voltage- the battery could have a shorted cell in which case it will lose voltage while disconnected.
- alternator could have bad internal diodes

- car wiring shorts, solder wires to a 12v bulb and put it in-line between the +batt and the +cable terminal. If the bulb lights at all (ignition off) there is power going (leaking) somewhere - pull the fuses one at time and see if the light goes out and, if so, Track down that circuit - Ex.: there is power that goes to the dome light all the time, a switch on the light and door (buttons) that also turn on the dome light [middle position is off]. The horn also has power that goes to it all the time and is grounded by the button on the steering wheel.
The thing about mk1's is the wiring was a hack-job from the factory.
Sometimes the best thing is to just disconnect a circuit or run your own wiring is something is problematic.

Copper lugs are all you need for making custom larger wiring and ground cables, junkyard cables are cheap source for heavy gauge copper wire.

Thank you for these pictures and your tips! The battery is brand new so that is now eliminated from a potential problem. I will be going through the diagnosis you and briano have recommended this weekend. Hopefully I find the culprit, or else I might be taking the alternator back to the refurbisher to double check their bench tests on the voltage output and regulator function.

Thanks again!
 

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There are some wire's that go from the roof into the back hatch that get messed up from the hatch opening and closing. Those are for the rear defrost and rear wiper. Mine, the wires are broken but I never use those things.
 

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Discussion Starter #9
Update: She's back in action! Thanks for all your advice. Turns out, there were a couple bad ground connections, and the parasitic drain was coming from the radio. I pulled the fuse on the radio to eliminate that and will investigate that further. But in the meantime, glad to have the car back on the road.

44468
 

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A lot of times they wire to power to the in switched fuse causing the drain if yours is digital face the keep presets is wired to unswitched power whereas the main power is wired to switched 12. the early ones were wired to 12v unswitched because folks like to hear radios while necking and polishing with the key off so if yours is oem be sure to turn off the radio by the knob or button, and not the keyswitch. good place to pick up switched 12v is from the defroster black/yellow wire to fuse.
 

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Update: She's back in action! Thanks for all your advice. Turns out, there were a couple bad ground connections, and the parasitic drain was coming from the radio. I pulled the fuse on the radio to eliminate that and will investigate that further. But in the meantime, glad to have the car back on the road.

View attachment 44468
[
Worth fixin. Thanks for the photos. I have those rims on my '76 Rabbit 5door, only one I've seen rolling.
Update: She's back in action! Thanks for all your advice. Turns out, there were a couple bad ground connections, and the parasitic drain was coming from the radio. I pulled the fuse on the radio to eliminate that and will investigate that further. But in the meantime, glad to have the car back on the road.

View attachment 44468
 
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