On the weekend did the geni to alternator swap, just as I've done numerous times over the years. Got it all hooked up, removing the external regulator etc. All good, except had to modify the new bracket (bolt holes didn't line up to my 850 block for some reason). Anyway all good. Fired it up and dash light stayed on. Checked all connections etc. Still no good. Got out the multi meter and checked at the terminals on the alternator, and no charge coming out. Re-checked the small wire going to the dash light and all OK. So must be faulty alternator or regulator. Gave up and went to bed thinking I'll pull it out tomorrow and send it back. Woke up in the morning and about to pull the alternator out and return it when I remembered something about that if your dash light bulb is blown, chances are it won't excite the alternator to start charging. However, my bulb wasn't blown, but then I remembered that when I had the speedo head out a few weeks ago I replaced the old bulb with a new red LED bulb - as the little lens was faded and with the red LED it looked better when it was on. So I thought maybe, just maybe, this was the problem? Sure enough, swapped back in an old filament bulb and bang - alternator charging like mad!

So lesson learnt, another issue when using LED replacement bulbs!

Thanks for sharing- it seems the led doesn't draw enough current to tickle the alternator- i had seen different threads on this- but easy to overlook - if it was me , it would have been the moment after I had un-necessarily swapped out the alternator that I would remember it

I came very close to pulling it out that night, just that it was getting late so thought I’d leave it till the morning. Glad I did though

The charge warning light is an important part of the charge sensing circuit. It has to be able to conduct current in both directions, which LEDs - being diodes - don't do well. A similar thing can happen if the globe blows.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

If you want to keep your LED globe or want the alternator to keep charging despite the bulb blowing you could put a resistor in parallel with the globe? Should be easy enough to just measure the resistance of a incandescent globe and get a resistor the same or similar (yes the led will flow some but I don't imagine it's too sensitive to a bit over).

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

I think this would be the circuit you'd need, it uses a bipolar led that will light with current flow in either direction (like an incandescent globe). R1 protects the LED and R2 simulates the resistance of the globe's filament. It would take a bit of thinking for me to calculate the resistor values though.



Tim

_________________
1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

Crikey - here i was thinking we just had to change a light bulb. Now i hear there are three mathematicians, two solderers,, one lucas expert and a parts interpreter needed to change a mini light bulb. (Said in jest.)

All I know is you guys are much smarter than me, that's for sure