I've just come back from a 4 mile lap and have some issues, surprise surprise as Cilla would say.

Over the last few weeks I've started the car on the drive no probs, getting the correct battery, temp and oil lights on when ignition is switched and then they got out once started.

5 mins in to the test drive and the battery light came on and stayed on for 5 mins and then went out. Drove for a few more miles, parked up at home, tried to restart and battery is dead.

Checked the connection blue wire from battery to alternator plug and that is ok.
Put a multi meter across the alternator large connection to the battery and only getting 9.5v which says the alternator is US? But it was all ok a couple of months ago when we drove it home 150 miles and then used it for work for a couple of weeks before I installed the new loom etc, can the alternator have really packed up just sitting on the drive??? 

Yes, Yes, and Yes.  It usually isn't  when you are running that the issue presents itself, it is when you start to stop the part.  (turning the car on or off) that Electrics goes bad…. as in it was working last night…. but not today.

Lightbulbs rarely go bad while they are on.  It is when they are turned on or off…..

usual suspects are.

Bad Voltage Regulator.
Bad Battery
Bad Exciter circuit.

Which type of Alternator, the Motorola with a plug
Or
Bosch that has two wires out the back Big one and a little blue one.  

If the exciter plug wire or blue one isn't got good connectivity then it can cause the car to run on battery and depending on the time of day and what you have running, as in defrosters heater lights and engine that will drain the thing rapidly.

My Wife drove a diesel from Atlanta to about 150 miles before she stopped on my car once during the day…
before the battery failed to crank the engine.  

Quick jump of the battery after "Plugging in the Alternator (motorola) and all was well.

Ground cables if you haven't replaced then Battery to frame and Frame to engine can cause a ration of iffy electrical issues…

Worst case is your Battery and Alternator are toast.  But good news is that you can remove both and take to a shop and have them tested usually for free.

So the answer is, with electrics Ca-ca can occur occassionally @ any time of the day for any reason.

so does the battery light no longer come on? if not, its clock or wiring fault, or duff alternator.

to rule out clocks and wiring disconnect the blue wire from the alternator and earth it, then switch ignition on. if the light comes on, its the alternator. if not, recheck blue wire and clocks

Guessing Motorola going on it has a two pin D plug it the top and the main positive to the battery is at 9 o'clock.

The battery is new so that's good, I've check the info on the exciter wire and it says plug F/03 blue wire, the plug at the fuse box doesn't have anything in that position!
I can't remember what wire I connected it to on the MK 2 loom  (which is now all taped up ) I've id'd the wire where I jointed the MK4 alternator loom near the battery to the MK2 and put 12v on it going back to the fuse box direction but still no battery light on the dash.

 

its A2/1 for mk2 golf, F plug is for MK3

basically unplug alternator, and earth the alternator pin, labelled D+ or L on the alternator. The other pin is DFM which goes to the ECU

if no light, then try stuffing an earth direct into the back of A2/1. if the light comes on, then work back from alternator or forwards from fusebox to find the fault. the mk2 loom has a spade plug near the battery live for the alternator, this a good place to start

CHEERS 

 

Off to investigate.

Morning John!

If I earth the blue wire at the spade connector near the battery I get the LED battery light illuminated on the dash, so does that mean my alternator is shafted or a bad earth?

that tells you the dash and wire up to that spade is all good, now plug the spade back together and earth the pin at the alternator end and see what happens. may want to double check the mk2 blue is spliced to the right pin, as i say its D+ or L on the alternator, usually pin 2 of the 2 pin plug. DFM is the ecu pin

A short direct to earth from the D plug (L pin) illuminates the LED … so that leaves the expensive bit I've taken the bushes out as per Haynes advise and measured the bushes at 7.5mm and the spec sheets in the manual says 5mm minimum then replace, the screws came undone really easy so guessing that they have been replace fairly recently!

Just a note, the description given earlier of the alternator pointed at the unit being a Motorola but mine is a Bosch, the labeling for the D socket is L & DFM as you John.

soudns liek its stuffed inside, even if the volt reg is bad the light should still come on with ignition i think?

its not just the brushes you also want to make sure the metal contact points between the brush pack and alt are clean. theres one round a scre hole, the other is on the side it touches som prongs inside the alternator. you'll see what I mean

If the Exciter circuit is bad as the Diode or the Bulb in the Cluster, you won't charge the field coils to start a charge.  

On the Makers of the Alternator the body can be either a Bosch or a Motorola.  The major differences between the kinds are a Plug in the alternator that is 3 wires 2 red and one either black or blue which is the exciter.

The Cabriolets use a Bosch with 2 wires a big one going to the battery, which can be via the starter then over to the battery, or from the Alternator to the battery.
This wire is on a big lug inside a phenolic block.  Then there is the smaller blue wire that goes back to the dash and from the dash back to the battery.



K2 is the LED that is biased to the ground through resistors and provides the B+ to the alternator  as it is marked as pin t14/12 to current track 5 Which is tied to the Battery.






The LED or Bulb draws power from the battery and places a small trickle voltage to the Alternator.  

When you start the engine, the bias is that the LED will light.  As your alternator starts to produce a charge, the More Positive voltage shuts down the diode and turns the battery lamp off, as the higher potential of the Alternator back bias's or stops current flow in the diode to put equal potential on both sides of the battery lamp

Now with that Caveat there is also a Under Frequency detect in the Voltage REgulator assembly that says the Alternator isn't spinning fast enough and that you need to increase the RPM of hte engine from 950-1100 (goose the throttle) to turn off the lamp, which is to be considered normal.

So the "IDIOT" light does a little bit more than what you think….It starts the alternator to charge, then monitors the output so that if your alternator goes out, or the belt flies off the pulley it starts to light up warning you that you are running off the battery.

This is imperative…..  If the Alternator Lamp/Battery Lamp doesn't come on with Key in and in the Run not start position, then you have an issue with the led/bulb or a wiring issue to the cluster from the battery.

You alternator needs a good ground from the Engine/Tranny  so it is also imperative to verify that your cables are clean and tight as well.  Battery to Frame horn, then frame to engine/tranny.  Some add an additional ground wire from a block bolt to the alternator housing.

if you take a jumper from the battery to the d+ or exciter wire when your alternator is spinning, then you should see the Alternator start to charge, that is a DVOM will go from 11.5 to 12V to 13/5 or greater.  If that happens then your issue is with the exciter circuit.

Hopefully I'll have good news in an hour!

Cheers John 😎

Happy Friday everyone.

… and Brian 

lovely job. onto the next problem

 The only things left are the rear wiper doesn't work and pretty sure the back lights in the dash are not working but I keep forgeting to check after dark!

I had to change the pinout on the rear multi plug as the the brake and tail lights worked visa versa.

The fusebox needs a more secure bracket but not really sure how, I'll come up with something, the speedo doesn't work but I'm fitting a recon gearbox (1.9 TDI ratios) at the weekend so can look in to that then.

Thanks again for all your help everyone, especially John and Brian for taking the time with all the detailed replies and advice.

Of to fit the new door cards now … what could possibly go wrong 

mk2 90spec fusebox hanger would be a good start, be sure its got both white securing clips included.

I didn’t have the dash lowers when I fitted this!

It the MK1 with the horizontal piece cut out, feels like it would be okay.

well its not gonna go anywhere, leave it and carry on with it for now. if 90spec a hanger comes available then grab it

mk3 golf one would take the mk2 fusebox, just not sure how well it will fit the mk1… plenty of those to pillage in scrappy anyway