[Mk2] [Turbo] Alternator nightmare

[Matty_GTS]

Ok so this time last year I replaced my alternator for a second hand one from someone on imoc. It ran fine and the car was used for about 500 miles before going off the road again.

Last week I got the car on road for the first time in a year and it drove for around 30 minutes before the car died. We connected it up with jump leads and charged it for 10 minutes before smoke started coming from the engine bay. Disconnected the alternator, charged again and manage to drive it home.

Today I have replaced the alternator for a new unit. Started her up and a steady 14.5V at the battery. After 5 mins of idling I drove down the road and a few miles later the warning lights on the dash for battery, IC fan? and engine warning. Tested the voltage and right down at 12V while running.

I am doubting that I have been sent a faulty alternator so I must assume that there is a problem with the cars electrics.

Can anyone make any suggestions where I should start? Are there any wiring diagrams for the charging/alternator circuit on the web? Is there a fuse from the alternator that could have blown?

Any help would be greatly appreciated! Thanks

[MartinF]

How old is the battery?

[Mr2Madlad]

Check the 3 thin wires in the multi plug are ok

What can happen is the copper wire breaks inside the insulation due to vibration, heat, water / corrosion right where they enter the multi plug.

The alternators regulator needs all 3 to work,

1 is Field / switched 12v (from ignition) check with volt meter red probe in connector black on nice exposed metal part of chassis.

1 is Ground - check continuity to chassis with ohm meter should be very low Ohms value under a couple or so.

1 is Sense - possibly live all the time - check with volt meter red probe in connector black on nice exposed metal part of chassis.

Do these checks without engine running but make sure ignition is switched off then on to check each, also make sure alarm is not immobilising while doing these checks.

If any one of these is missing alternator not work / not work right.

Solved my issue so from personal experience wires do snap / corrode internally.

Hope this helps

Mr2MadLad

[Driftlimits Performance]

none of the wires are an earth. All 3 carry voltage. 2 of which should have the power to light a light bulb. If not run wiring from alternator to fuse box. Never just change an alternator, check all the wiring first.

[Matty_GTS]

Hey Luke, how you doing? Been a while

Ok so the 3 pin plug doesn't look great, looks like it has gotten hot (probably when the removed alternator was smoking away...).

I couldn't get anything with the volt meter probes, had to push a length of wire into each plug opening to get a reading. With the ignition on I got 12V at all of the pins.

I suppose it is possible that they are not making a good connection within the plug. It doesn't 'click' into place anymore, just pushes in as far as possible. Is this a part I can find at the dealers? Anyone got one I could exchange for beer tokens?

If this is ok is there anything else on the car that could be causing the lack of charge?

Checked the 120A alternator fuse link and 7.5A sensing fuse in the box and they look fine.

I am struggling to believe the brand new alternator would work for 10 minutes until the first time I gave it full beans in 1st & 2nd and then packed up...

Any more suggestions? Thanks

[Matty_GTS]

All 3 carry voltage. 2 of which should have the power to light a light bulb.

I didn't use a light bulb but two do spark nicely when touched on the bodywork and one does not. So I would say that the above has been proven

[Driftlimits Performance]

assumption. The mother of all willy ups!

[Matty_GTS]

I forgot to post an update...

New alternator (in the words of the man at my local alternator) is a load of cheap Chinese s**t! He tested it and it was dead! No real surprise.

Before I could say anything he was stripping down my genuine alternator, found the burnt diode, rummaged through a pile of alternators and pulled out one for a tubby and 5 minutes later I had a working alternator

These little back street shops / garages are great.

[toxo]

The diode pack is a fairly common one as it happens, pretty much anything of the age & engine size with a Denso alternator has the same part. I think I used one from a Honda.

[Racer7]

Don't suppose you have any pictures from this escapade.

Wondering if mine might be a similar situation - before I go spending out on a new alternator. (car hasn't been driven for year and I've learnt that sometimes rust build can cause the fault).