thecuist1

Hopefully final update on this issue. I purchased a brand new alternator and once fitted the car is now running fine and battery is charging at the correct 14.5 volts. Thanks for all your help Breezy Pete.

Wow well there you go, who would have thought a 12v circuit could drop nigh on 11v and still be functioning correctly, guess I will go ahead and order a new alternator and hopefully that will resolve the issues. Thanks again for your help I will come back and report once I have fitted the new alternator.

Yes being on the west coast of Ireland is a bit of a nightmare for motor parts to be honest. My local motor factors just told me there are 4 variants of that alternator and they couldn't supply one which is odd. I can buy online but postage and returns can be a pain but I have seen one for around €100 delivered but I'll wait for your voltage reading b4 ordering.

Hmm well I'm leaning towards a weird alternator fault, probably the next step is to pull the alternator again and either get it bench tested by a specialist or just buy a new one and hope. I hate throwing somewhere in the region of €150 at a problem and hoping but I doubt specialist testing would be much cheaper. If you can test your voltages with blue wire connected that would be interesting, its the last anomaly that we haven't cross checked. I understand that it could be a bit of hassle though, if its positioned similar to mine the exhaust and heat shield prevents easy access to the plug connectors. I wish my alternator was positioned the same as on the diesel, there was no way I could remove the voltage regulator without removing the alternator. Thanks very much for your input thus far.

That would make sense, presumably the blue wire sends a signal back to the battery light via the control module to verify that the alternator is outputting 12+ volts. I wonder what the path is from the blue wire through the alternator. Given that I replaced the voltage regulator and that made no difference, maybe there is an issue with the rectifier part of the alternator? I also tested the diodes and they seem to be functioning correctly though.

Yes the other anomally was my Voltage dropping to 2v when I have the blue wire connected would be interesting to see if yours was the same. I think we have reasonably verified that 50ma should be enough to fire the alternator but i'm still baffled by the voltage drop. Connecting directly to the battery would also have made sure the alternator was getting 12v wouldnt it?

yes, I have removed some insulation on the blue wire just b4 it enters the alternator plug and have a crocodile lead on there. I am measuring 1.85amps between battery + and the blue wire while its connected to alternator (and disconnected under the gearbox, so essentially isolating the alternator from most of the loom. Its strange that you are reading more or less the same amps as me feeding your alternator though. That implies that my blue wire is working correctly.. However, the alternator only worked when I supplied 1.85amps direct from the battery, so, the normal amps (in your case 53.3ma) works ok on your car but my amps were almost exactly the same at 50ma were not enough to excite the alternator. That seems to confirm an alternator fault in that mine requires 1.85amps to fire up..

Thanks for replying so swiftly. I am reading 1.85A between battery and alternator terminal (thats with the gearbox connector unplugged)

Hi Pete I purchased a DC meter and read 50ma on the blue wire with ignition on and wire disconnected testing to earth. Then I tested with the wires connected to alternator and I'm getting 41ma. (wires connected in series between the 2 sides of the plug under gearbox. This remains the same whether the B+ terminal is connected or not. What does this tell you if anything? Thanks Peter

Couldnt find a meter locally so I'll pick one up tomorrow hopefully and give an update.

OK, I have to go out and pick the missus up and I'll see if I can pick up a cheap meter with DC current testing on the way back, then I'll check the current draw on the blue wire to ground and get back to you. Thanks for your input. I'm called Pete too btw, grew up in Towcester. Northamptonshire. Chat soon.

Hi Breezy, sadly not. I only have AC current measurement. I read the section regarding testing current draw on the blue wire. I can buy a cheap auto multimeter if you think its worth it. What were you thinking I should test?

Hi all. I thought it might be best to resurrect this thread as it has loads of pertinent information regarding my problem. Hopefully the super knowledgeable guys on this thread are still active and can give me some input. I have a Skoda Fabia 1.2HTP 04reg which came up with the battery warning light while driving, this was intermittent for a day or 2 but then stayed on constantly. The alternator is def not charging the battery as battery voltage is only at 12v with engine running and alternator connected, there is also no voltage output from the B+ terminal on the alternator. The battery light is on when ignition is first switched on so after reading this thread I thought this precluded the common broken wires to alternator but I checked them all anyway. I checked the alternator plug, the plug under the gearbox, removed the scuttle and checked continuity from the blue wire all the way to the alternator all seems good. This led me to believe that it was possibly a faulty regulator/brushes so I got a new regulator fitted it to the alternator but still no charging. Here is where it gets strange... I checked Voltage on blue wire while the alternator plug is off and I have around 11v with ignition on and engine off and with engine on. However, when I plug it back into the alternator with engine either off or on the voltage drops to around 2v only which doesn't seem to be enough to excite the coils. My next step was to cut the blue wire where it exits the bulkhead and run a wire directly to the connector on the back of the alternator thereby bypassing the whole blue wire run around the loom to eliminate shorts or voltage leakage but the voltage still drops to 2v when the alternator is connected. I then decided to connect a wire directly from the positive terminal on the battery straight onto the blue wire while the plug was connected to alternator (scraped off some insulation and used an alligator clip) and voila the alternator started charging and I had 14.5v at the battery, the battery light also went out. So to summarise: I believe I have eliminated a potential break in the blue wire ( I also checked the blue wire where it connects into the onboard control unit under the dash) I can get the alternator to work by powering the alternator straight from the battery, I also checked the alternator diodes using HatboyHarveys method and I have 0.950 one way and open circuit the other, (hatboy had 0.450 one way and open circuit the other) I'm left thinking that maybe my alternator is faulty with some weird voltage drain not related to voltage regulator, or possibly the onboard control unit is faulting in some way which is causing the voltage drop when the alternator plug is connected. Does anyone have any thought please? Thanks in advance