Alternator light not lighting (after mishap)

Discussion in 'Mech Tech' started by Aang, Jun 10, 2019.

  1. First a bit of back story: After casually drilling holes under the dashboard in my 1973 (type 4 motor) I let out quite a lot of smoke and caused alternator light to shine. I turned off battery, let the smoke die down and fixed the loom near the hazard warning switch - there was a fairly fat red wire (permanent 12v) and a thin blue wire (alternator light). Now the alternator light doesn’t shine :( In addition the right indicator stalk doesn’t work - I do not know if this is connected or a red herring.

    So far I’ve established bulb is fine - it has 12v with ignition on and if I ground the bulb it lights up. The alternator works just fine with 14v at battery when engine is running (I thought it needed to alternator light to ‘activate’ the alternator). I’ve tried a new voltage regulator with no change.

    As I say, the right indicator light doesn’t work, but left indicator work and light up both lights on dash. The hazards work just fine, as do the headlights. All fuses look fine.

    I can’t find the blue wire in the engine bay.

    What have I broken and how do I fix it? Do I even need the alternator light if it seems to be working fine (although I do really want to sort it). Thanks in advance!
  2. The blue wire in the engine bay should be connected to the smaller terminal on your alternator.

    This terminal is earthed at the alternator when the engine is off, but positive when the engine is running.

    The dash bulb is powered by the ignition, and earthed via the blue wire at the alternator as above. :thumbsup:
    Last edited: Jun 11, 2019
    Lasty likes this.
  3. If the engine was running at the time you released the smoke it could be you blew the rectifier pack in the alternator.
    If the engine was stopped you have not managed to join up the alternator warning light wire properly between the dash and the alternator.
    Some alternators will self excite depends on magnetisation of the rotor.. once it is spinning and producing 14 volts it really does not need the warning light circuit to be present as the regulator taps its power off the alternator warning light terminal directly. Which is powered by (small 1 amp ) diodes picking power out of the big rectifier.
    This is why I think you have burnt some wiring rather than damaged the alternator.
  4. Are all the brown earth wires on the back of the dash ok
  5. Thanks for thoughts. I’m sure my repair of blue wire is good as the alternator light blue wire is meant to be joined to brake warning light somewhere behind dash, and they are good with the multimeter. I rechecked all the brown earths in that area and they are good.

    I think I am missing a blue wire connecting the red wire plugged into voltage regulator to a female space connector with two wire leaving it - which currently isn’t connected to anything. The wiring diagram shows two blue wires, but I have one blue one heading to the front of the van and one blue and yellow one heading to the fan (butchered near the fan already). On close inspection it looks like the red wire into regulator has remains of an old wire broken off.

    My current plan is to splice in the two blue (and yellow) wires to the red wire from alt to regulator. Although it doesn’t seem right to haphazardly join red and blue wires together - only the kind of thing someone who drills into stuff without looking behind would do! If this fixes it, it does mean the drilling was nothing to do with the lack of light and I was blissfully unaware of previous lack of light.

    ps. the engine was not running while I was drilling, so I’m glad you think alternator diodes should be fine.

    It does mean the indicator is another problem to fix!

    Attached Files:

  6. All sorted. It was missing the blue wire joined with the red wire at the regulator.

    I also sorted the jaffa brake warning light, but that seems the be working exactly the same time as the alternator light - is this normal? It had a few wires disconnected prior to my fiddling. It does share the blue wire from the regulator which didn’t make sense looking at the wiring diagram - and still doesn’t make a great deal of sense...
    Edit: Brake warning light is working normally:
    Although I’ve now read about a handbrake light - is that even a thing?!?

    Also traced indicator problem to lose wire in 8 way connector block behind dash. But not satisfied with two fixes in one night I’ve also ordered some replacement plastic bits so the indicator may self cancel and not flop down and start indicating left without warning.
    Last edited: Jun 12, 2019
    Iain McAvoy, Valveandy and just-paul like this.

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