Possible alternator issues??

Hi fellow Mk1 owners,

just fitted a new Pierburg fuel pump to my Mk1 Gti as the cheap and nasty one i fitted 4 years back died! The question i have is when the car is started you can hear the pump buzzing nicely but when I put the headlights on the pump not significantly drops and sounds like its struggling. I expect this to happen slightly but not to this degree. Do you think it could be related to an old worn out alternator?

Thanks for any help given 

stick a volt meter on the battery
that will tell you straight away

Well, an alternator that is functioning will produce about 13.85V-14V DC in relationship to ground.

If you turn on the headlights and the voltage drops then you need to do a little trouble shooting and an DVOM is going to be your Friend.

The Biggest issues that I have seen over the years are Very CRUDDY ground connections.   Why you ask?  Because the marvelous Bosch/VW engineers decided that they should use an unshielded twist braided ground lead from the battery to the frame and then tie it and run it to the engine.  The single point of ground for the alternator is the bracket that holds it in place, and even tho it is a big hunking piece of steel, it is subject to the same thing as the silly cable, corrosion, crud oil and grease which takes away the connectivity of the ground and makes it resistive.

Easy Peasy to check with a DVOM, take the ground off measure the voltage on your battery with a running car fully charged you should read 12.5 to 13V. between posts. (key off) and you measure the battery between the posts.

Now connect the ground, and measure the voltage between the Battery positive and a good frame point on the car, is there a difference of greater than .05V?  If so then REPLACE YOUR GROUND Cables between the battery and the frame and the frame to the engine.

Clean the Tie point on the frame horn so it is nice and shiny, you can order a new OEM style of cable that too is unshielded, but I strongly urge you to wrap the cable in canvas/tar based electrical tape, or even the vinyl (DO NOT BUY CHEAP TAPE) use a good quality tape 3M Scotch Brand.  Or you can go to the auto supplier of your choice and buy 2 off the shelf cables and a 3 large
flat washers.  Once cable will have a battery terminal on it, (I prefer ones that have extra take offs so I can get the silly ground rings off the nut).  On the flat side I usually use a BFH (big Flipping Hammer) and totally flatten the end that attaches to the frame. I place a flat washer on the stud, and route the battery cable on it, followed by another flat washer..I take the Battery to battery jumper that is about 12" long and flatten both ends with the BFH.  I add that to the frame stud, and add a flat washer over it then the 13mm nut.  Why, you ask? So I get maximum surface area for my cables and lower the resistance…. Once I have them firmly mounted to the frame, I spray the attachment point with Battery Protective Spray, it is usually a purple or blue color, it will seal the ground point against rain, salt and other things the world will throw at it.   

Lastly I attach the free end of the battery jumper to the mounting bracket on the transmission, and or the double stud point where the engine is bolted to the tranny, after removing that bolt and cleaning the stud on both ends and using never-sieze or copper grease as y'all call it so no corrosion can build up between the threads of the stud and the block/tranny.

Now re-check your voltage tests and you will see that wally, there is no difference…..

On the alternator, I use a length of wire that will reach from one of the case nuts of it, to the engine block bolt.
I use a good gauge of wire usually 14 and Ring connectors that I not only crimp but solder to the wire.  I attach a smaller ring to the case nut of the alternator, and the other usually larger to the block so that my Alternator is Tied to the block by a good tight electrical connection.  

With these connections made start your car, and if your alternator is good, you should now see a Jump in the voltage at the battery and your iffy issues will cease.  You may also want to check your grounds on the fuel pump and possibly tie it direct to the frame.

Speed Round

One of the easiest and cheapest mods you can do to your car is add relays for the headlights.  You will accomplish 2 things.  Increase the Current and Voltage at your lights and make them brighter.  You will be off loading hi-current devices off your headlight switch and making the switch less prone to failure.

Head lights are high current devices and the relays shorten the run of wire to them by about 10 feet or 3 meters.

You can buy relay kits from Ebay that are all wired or plug and play, but be sure that you get Ceramic Headlight sockets on ones that you buy.  Since I am old school, I made my own, and since the original design of mine I added a 3rd relay that allows me to operate all the element or filament on my rounds (7") bulbs at the same time I use my highs.   

With a meter you will see a 1.5 to 2V difference in voltage to your headlights.

Here is how I dude that.
https://www.volkswagenownersclub.com/threads/relaying-your-head-lights.32215/

If you haven't had your alternator tested I would urge you to do that as your voltage regulator could have iffy brushes, and or is bad.

Then as you are having your alternator tested, have them check your battery as well.

My 2 Cents.

Oh, and here is a thread on iffy grounds that I did
Ground effects and the repair of your car. | VW Vortex - Volkswagen Forum

You didn't think I would have a one or 2 sentence answer did you…

Briano1234 said

Well, an alternator that is functioning will produce about 13.85V-14V DC in relationship to ground.

If you turn on the headlights and the voltage drops then you need to do a little trouble shooting and an DVOM is going to be your Friend.

The Biggest issues that I have seen over the years are Very CRUDDY ground connections.   Why you ask?  Because the marvelous Bosch/VW engineers decided that they should use an unshielded twist braided ground lead from the battery to the frame and then tie it and run it to the engine.  The single point of ground for the alternator is the bracket that holds it in place, and even tho it is a big hunking piece of steel, it is subject to the same thing as the silly cable, corrosion, crud oil and grease which takes away the connectivity of the ground and makes it resistive.

Easy Peasy to check with a DVOM, take the ground off measure the voltage on your battery with a running car fully charged you should read 12.5 to 13V. between posts. (key off) and you measure the battery between the posts.

Now connect the ground, and measure the voltage between the Battery positive and a good frame point on the car, is there a difference of greater than .05V?  If so then REPLACE YOUR GROUND Cables between the battery and the frame and the frame to the engine.

Clean the Tie point on the frame horn so it is nice and shiny, you can order a new OEM style of cable that too is unshielded, but I strongly urge you to wrap the cable in canvas/tar based electrical tape, or even the vinyl (DO NOT BUY CHEAP TAPE) use a good quality tape 3M Scotch Brand.  Or you can go to the auto supplier of your choice and buy 2 off the shelf cables and a 3 large
flat washers.  Once cable will have a battery terminal on it, (I prefer ones that have extra take offs so I can get the silly ground rings off the nut).  On the flat side I usually use a BFH (big Flipping Hammer) and totally flatten the end that attaches to the frame. I place a flat washer on the stud, and route the battery cable on it, followed by another flat washer..I take the Battery to battery jumper that is about 12" long and flatten both ends with the BFH.  I add that to the frame stud, and add a flat washer over it then the 13mm nut.  Why, you ask? So I get maximum surface area for my cables and lower the resistance…. Once I have them firmly mounted to the frame, I spray the attachment point with Battery Protective Spray, it is usually a purple or blue color, it will seal the ground point against rain, salt and other things the world will throw at it.   

Lastly I attach the free end of the battery jumper to the mounting bracket on the transmission, and or the double stud point where the engine is bolted to the tranny, after removing that bolt and cleaning the stud on both ends and using never-sieze or copper grease as y'all call it so no corrosion can build up between the threads of the stud and the block/tranny.

Now re-check your voltage tests and you will see that wally, there is no difference…..

On the alternator, I use a length of wire that will reach from one of the case nuts of it, to the engine block bolt.
I use a good gauge of wire usually 14 and Ring connectors that I not only crimp but solder to the wire.  I attach a smaller ring to the case nut of the alternator, and the other usually larger to the block so that my Alternator is Tied to the block by a good tight electrical connection.  

With these connections made start your car, and if your alternator is good, you should now see a Jump in the voltage at the battery and your iffy issues will cease.  You may also want to check your grounds on the fuel pump and possibly tie it direct to the frame.

Speed Round

One of the easiest and cheapest mods you can do to your car is add relays for the headlights.  You will accomplish 2 things.  Increase the Current and Voltage at your lights and make them brighter.  You will be off loading hi-current devices off your headlight switch and making the switch less prone to failure.

Head lights are high current devices and the relays shorten the run of wire to them by about 10 feet or 3 meters.

You can buy relay kits from Ebay that are all wired or plug and play, but be sure that you get Ceramic Headlight sockets on ones that you buy.  Since I am old school, I made my own, and since the original design of mine I added a 3rd relay that allows me to operate all the element or filament on my rounds (7") bulbs at the same time I use my highs.   

With a meter you will see a 1.5 to 2V difference in voltage to your headlights.

Here is how I dude that.
https://www.volkswagenownersclub.com/threads/relaying-your-head-lights.32215/

If you haven't had your alternator tested I would urge you to do that as your voltage regulator could have iffy brushes, and or is bad.

Then as you are having your alternator tested, have them check your battery as well.

My 2 Cents.

Oh, and here is a thread on iffy grounds that I did
Ground effects and the repair of your car. | VW Vortex - Volkswagen Forum

Great thank you so much for all the information