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Alternator warning lamp staying on (phoenixd1)

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Post by Phil Bradshaw » Club admin » Sun Feb 09, 2014 12:16 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
phoenixd1 wrote:The alternator is sort of okay according to the AA who rescued me when it broke down in the middle of the road in rush hour traffic! THAT was scary :o apparently the diode is faulty because it is feeding back to the battery. The battery light stays on when the key is removed from the ignition draining the battery. And because it's not charging the battery, I am using more than the battery has juice... hence the reason the van just 'stopped'. I can get it repaired apparently, but I cannot find anywhere that offers a new Bedford alternator for less than £150!! When I get it repaired (I don't know if I can do it myself) I will get new brushes and diodes as a preventative measure... what do you think??
Faulty rectifier diode/s can cause the warning lamp to stay lit when the ignition is switched off but it's a rare fault because normally diodes burn out rather than short through.

Check the wiring first by disconnecting the thin brown+yellow wire from the back of the alternator. Be wary of the thick brown wire there: it's a direct feed to the battery so don't be prodding it with anything metallic if the terminal insulation is missing/damaged!

If the warning lamp goes out with the brown+yellow wire disconnected then the fault is in the alternator.

If the warning lamp stays on with the brown+yellow wire disconnected then the fault is in the wiring. Fault then may be a 'live' feed wrongly connected into the warning lamp circuit (i.e. brown+yellow wire) with the earth return finding its way through the instruments and ignition system.

Once you've established a faulty alternator and to save a few quid disconnect the battery earth lead, unbolt the alternator and take the unit to an auto electrician: they'll be best placed to source bits for Lucas or Delco units normally installed on the Vauxhall OHC (slant) engine and test the repaired unit before handing it back.

DiY repair is feasible but there's only a Howto done for Lucas ACR units (black plastic end cover). Renewing the rectifier involves a soldering iron, 100 Watt minimum, 200 Watt if the slip ring is renewed at the same time and that's a good idea anyway because the centre wears through after a few sets of brushes.

If it's a Delco unit with all aluminium alloy casing then no soldering is needed but new brush gear may be required because sometimes the brush holder breaks when dismantling the unit if the slip rings have significant wear ridges on them. Soldering iron (200 Watt) comes in if the slip rings go under-size when cleaned up and need renewing. I'd have to catch up and finish the Howto for Delco units too ... but there's most of what's involved in putting it back together in A cooked engine (about half way down the first page).
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

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