Morris Minor Owners Club

Wow you guys were bang on. PO wired the dash warning bulbs the wrong way around.

So just leaves question that if fan belt is ok & reading across the battery terminals of 12.4V at rest and 14.2V when running. Why is the now correctly wired (green & white) ignition warning light on & flickering when engine running and revs up?

Weirdly ignition light now stays on even when key is removed

Wes wrote: ↑Tue Apr 15, 2025 5:37 pm Why is the now correctly wired (green & white) ignition warning light on & flickering when engine running and revs up?

The Ign Light has a Brown/Yellow one side that goes to the Alternator/Dynamo and a White that goes to the Ign Switch.....

Wes wrote: ↑Tue Apr 15, 2025 5:37 pm Wow you guys were bang on. PO wired the dash warning bulbs the wrong way around.

So just leaves question that if fan belt is ok & reading across the battery terminals of 12.4V at rest and 14.2V when running. Why is the now correctly wired (green & white) ignition warning light on & flickering when engine running and revs up?

See my earlier post on the other thread? I expect it is (at least) the diode bridge which has failed.

You can, of course, discount my diagnosis of your apparent problem.

oliver90owner wrote: ↑Tue Apr 15, 2025 7:30 pm

Wes wrote: ↑Tue Apr 15, 2025 5:37 pm Wow you guys were bang on. PO wired the dash warning bulbs the wrong way around.

So just leaves question that if fan belt is ok & reading across the battery terminals of 12.4V at rest and 14.2V when running. Why is the now correctly wired (green & white) ignition warning light on & flickering when engine running and revs up?

See my earlier post on the other thread? I expect it is (at least) the diode bridge which has failed.

You can, of course, discount my diagnosis of your apparent problem.

I wouldn't totally discount that, I guess it depends which diode or diodes have failed. But I'm surprised at a steady 14.2v with the light on.

Baring any other faults in the wiring, the only real option is that, as Oliver suggested, one of more diodes has failed in the Alternator, so when the Ign Sw is off, as indicated by the * on the image, the battery is feeding as shown by the blue arrows via the Alternator and eventually finding an earth, probably via the Coil... Hopefully you disconnected the battery overnight, but when you go back to the car, with the Red Light on and the Ign Sw off, unplug the alternator.
That should put the light off.

If it stays on, you've got yet another problem.....

This is a reasonably clear video of checking an alternator, the diode check is at the half way point, but the whole video is quite good.
https://youtu.be/dhf6IdBbE3Y?t=312

Thanks will do this later today

But blow me. Tried the car this morning. Turned on battery and no lights! turned key and both yellow & red come on. start car yellow goes out but red stays on blinking/flickering. Still getting 14.2V at the battery, turned engine off, pulled out key and red light still on!!

Can I just clarify that you have had the car for a while and it never did this behaviour with the charging light before? I realise it's confusing because the oil light was being the charging light but now we are talking about the correct charging light on the speedo. This is new abnormal behaviour?

Stephen

I've had the car about 6 months and done about 400 trouble free miles. Not noticed this issue until i put the car in the garage last weekend. Also weirdly coincided with me fitting ESM's gear stick anti rattle kit!

Really stupid question but as i know its not the oil pressure its tempting to ignore the ign light and run the car. Is that asking for trouble? I have my first car show at the weekend (about 15 miles away).

Well there is an earth strap from the gearbox to the crossmember but I can't see how that can possibly have been disturbed by fitting the anti-rattle kit so it does seem like a coincidence.

Stephen

svenedin wrote: ↑Wed Apr 16, 2025 1:31 pm Well there is an earth strap from the gearbox to the crossmember but I can't see how that can possibly have been disturbed by fitting the anti-rattle kit so it does seem like a coincidence.

Yep i've discounted that as just pure coincidence

Now we know what we're dealing with, I'm really coming down on the side of a failing Diode Pack on the Alternator.
Not the whole thing, just 1 or 2 of them at the moment, because I think that fully serviceable the Alternator would be giving about 14.6v.
I may be wrong, but I wouldn't be surprised if there's about 1v of AC sitting with that DC output....

So is it safe to drive? what could happen if diodes fail? fire?

Wes wrote: ↑Wed Apr 16, 2025 4:26 pm So is it safe to drive? what could happen if diodes fail? fire?

Unlikely to have a fire, but could easily knacker the battery and perhaps ruin any other electricals like radio.
It just depends on the mode of failure, whether they go open circuit or short circuit.
Something like this can often be a cascade failure, i.e. after the first one goes, it adds stress to the others so they all start failing.

Check it out using the info on that video..

Which alternator model have you got?

Messaged the PO last night as there was no mention of an alternator swap in his comprehensive ownership notes. He had the car 13 years and done about 50,000 miles. But he informed me that it was already on this alternator when he bought it. So im just going to bite the bullet ang get a new alternator. Only about £60 from ESM but they are out of stock. Oh well not going to the show on Saturday then

ive not removed the offending one yet and the sticker on the side of the alternator has gone AWOL so not sure what type it is.

Thanks again for all your great help in diagnosing my issue.

Have you actually checked it to confirm the Diode Failure?

The Diode Pack (aka Rectifier Pack) is about £15 and easy to change.
After doing over 50,000 miles it might just be the brushes worn, they're perhaps £5.

Don't change what you haven't confirmed, it's a very expensive way of fault finding

If you have a good battery and it was fully charged, disconnecting the alternator should not affect the battery too much - as long as the car is a) not driven in the dark and b) only started on a very few occasions for a 30 mile round trip. Recharge the battery at the earliest opportunity. Starting with the handle is an alternative to using the starter motor and don’t leave the ignition switched on with the contact points closed (disconnecting a coil wire would ensure no power loss).

Bingo