Club 80-90 Forums

I have just replaced my alternator because the old one stopped charging.

The new one does not have the same plug fitting so I have cut off the old plug and crimped connectors on, however I am having trouble getting the wiring right.

I have 2 reds coming from the battery, looking at the wiring diagram these both go to B+ and the Blue (dash warning) goes to D+ and looking at the old plug would confirm this.

However, as wired above the alternator does not charge and the dash light stays on still, I am now wondering if the fault was elsewhere

If 12v is applied to the D+ terminal the alternator will kick out 14v, so should the blue dash light cable supply 12v to this terminal, at present this lead seems to be to earth.

Kerr

Right, to answer my own question, yes the D+ needs a 12v supply via the warning light ! to get the alternator working.

I do not have 12v here and its stright to earth, anybody goy any suggestions of where to start fault finding ??

Kerr

the fault was buying the wrong alternator my friend

can you tell me if the regulator was checked on the old one?

are you'r temp and fuel guages reading normaly? how are you checking that the blue wire goes to ground?. you may have a problem on the dash panel circuit- maybe the diode or the zener diode .

No Regulator was not checked Kev, I just exchanged it.

Although the terminals are different they have the same connections (if that makes sense) B+ and D+

I have since cut into the cable behind the instrument cluster and the light has gone out, then connected a fresh cable from the instrument cluster, if I then touch the other end to the body the light will come on, but still do not have 12v present to supply the alternator.

The test above tells me that the original cable is touching the body somewhere, as its not connected to the alternator and the light would still stay on.

All other lights are working fine, including the temp sensor etc

Getting a bit fed up with this van at the mo'

Kerr

I am doing this very much from memory but I believe that the warning light should have an ignition switched 12v supply to one side and the second side going to the alternator.

That way, when the ignition is on and the alternator is stationary, the current (through the link described above) exciting the field winding of the alternator is sufficient to light the warning lamp. Once the alternator is producing a charge, it provides it's own 12v supply to the exciter terminal and the voltage is balanced across the bulb. Therefore, no flow and no light.

I hope that helps. I will try to make time to check the current flow diagrams and confirm if this is correct.

Garyd

Thanks Guys

Garyd, I have learnt a lot this afternoon and what you say sounds about right.

I have found a problem with the original 12v feeding the alternator from the warning light and bypassed that and now have 12v on the other end of the cable with the igition on.. however

When I connect this 12v to the D+ terminal to start/excite the field winding it still will not start to charge, but when I put a feed from the battery to this terminal it will kick in and charge.

Another thing confussing me is that when the new 12v supply from the warning lamp is connected up to D+ the voltage seems to be dragged down to about 1.5v - I am suspecting that the new alternator may have a fault or has been damaged when the original cable was straight to ground?

Kerr

a few things, with the igntion on but the engine not running you should have next to zero volts on the d+ terminal[wired correctly]. the blue wire goes to a diode before the warning lamp. some alternators are designed to not charge if the voltage on d+ is below a certain voltage.i fitted an alternator to my vw t2 ,it wouldnt charge untill the battery was charged to 12.6 volts[the instructions said the same].

Sounds as if you're well beyond this but is B+ the charge warning light terminal rather than D+?
potentially useful link below:

http://www.kampenwagen.co.uk/split%20charge%20relay.htm

good luck
jim

vanjam,the guy on that link has his wires crossed[b+ goes to the battery ].
the rest of the stuff seems ok.

Finaly solved ..

New cable wired in from the warning lamp to excite the alternator and the new alternator seems to have been faulty, replaced and all is ok.

Thanks for your help all....what a fun weekend that was.

Kerr