Morris Minor Owners Club

Need help diagnosing odd alternator 'charging' fault please.
Car is 62 Trav with neg earth/alternator conversion - done when totally restored from a wreck in 2007. Volt reg still present but used only as jn box (all brown + brown/blue conected at A1, all black at E - no others). Worked fine all last year, but has been 'laid up' covered in a dry garage since earlier this year while I worked on another Trav restoration - no battery connected.

Took for a drive yesterday (using charged battery from other Trav) started fine but the ign light stayed on when engine was running - only dimly at tick over, but if anything got brighter when revs increased. Then after some use it went dim, even with wipers/lights on, but still stayed on. Checked fan belt - was loose! Ah ha! Sorted I thought - tightened it up - still same result re ign light - Boo Hoo!
Drove for about 8 miles overall with no noticeable effect on performance.

Read a lot of threads last night and did some diagnostics this morning.
1. Pulled lamp holder out of speedo to check for earth fault - still did the same thing.
2. Tested voltages as follows: Across battery, ign off, no load: 12.8 - 13v, Field wire socket on alt to earth: 12.4v, across battery, engine running: when ign light is bright 17.8v!! when light dims a little 13.8 - 14.5v. Every now and again light will brighten for no apparent reason and volts across the battery go up to circa 18v again.
3. Tried to check for magnetism of alternator body, but no noticeable attraction when ign off.

I infer from the abvove (to be corrected by those who know!) that the alternator is producing adequate, if erratic, output. What puzzles me is why the light remains on even when the alt is putting 14v+ across the battery, as this should be sufficient to balance the route to earth through the alternator. (If I'm correct in understanding how the ign light works!)

I suspect a dodgy regulator/diode or an earth fault in the alternator, but before I off to the scappy for a replacement I'd like some confirmation that it's not something else (Esp as the alternator is less than 18mo from new from MGM). Also how do you replace just the reg/diode and is this something I should try given it's such a nearly new item?

I disconnect the battery with an isolator when car is not in use.

Thanks...

It sounds like the ign light is not seeing an earth properly. It could be the wiring from regulator as it apears that the alternator output is unstable. Also check the engine earth. One other thought is the type of isolator you are using, If it's one of those brass bar type ones with the knob you unscrew then I've had problems with these before now.....

17V

I think the regulator in your alternator is kippered. I wouldn't take it anywhere else until you fix the alt unless you want to kill your battery

Hello M,

the ignition light is not earthed as such, as all the other lamps in the car are, but is across the battery and the alternator. A differential voltage lights the lamp, i.e if the battery voltage is higher than the alternator voltage, as it is when you switch the ignition on or if the alternator voltage is much higher than the battery voltage. Yes, typical fault with Lucas ACR alternators, failed regulator. The good news is that replacement alternators are cheap. i personally wouldn't even bother trying to fix one.

Alec

Matt wrote:17V

I think the regulator in your alternator is kippered. I wouldn't take it anywhere else until you fix the alt unless you want to kill your battery

^^^WHS^^^

I assume the battery was fitted right way round ! Only way the volts could rise so high if the connection to the battery has been lost - otherwise the battery would 'sink' the volts with overcharging of course. So - I think you have a bad connection between battery and the lead from the alternator, Suggest you check the volts actually on the battery posts and see what results. But running like that may have ruined some of the electronics in the alternator. Check all connections very carefully before fitting another alternator in case it goes the same way!

Thanks for the help:

1. Yes I do have a brass bar isolator
2. Measurements were across the battery terminals (apart from field voltage of course)

Interestingly while I was changing the fuel pump (and isolating, reconnecting the battery) the problem 'went away' - ie., the light started to behave normally. So the isolator (which is on the earth strap) might be the problem. I will check the alternator leads and I think I'll get and carry a replacement alternator just in case! I will report back if the problem recurs.

It's definitely a loss of connection to the battery - so check everything very carefully and perhaps just put a link across the isolator meantime. If the battery was indeed showing 17 volts then it would be overcharging massively - and gassing - so beware of creating any sparks. It will also blow your lights if you turn them on at that voltage. I do suspect your meter may be showing slightly high too - - because an off load battery doesn'y usually show 12.8/13 volts - although yours may if it's been getting charged at 17 volts !

Hello BMCE,

I was under the impression that losing the battery connection would blow the regulator, which is why competition isolating switches have a resistor to earth the system when the switch is opened if the engine is still running?
Certainly a high charging voltage will soon damage the battery and usually is quite obvious by the strong acidic smell around the battery.
I have had two 17ACR alternators fail with regulator problems and I would suspect that this is the cause here (As have others going by various forums I visit). A faulty battery terminal isolator would surely be obvious as the starting would be affected?

Alec

Well yes Alec - it CAN ruin the regulator, but may not do so right away. I have had battery terminals come loose in the past (on Minis) and 'got away with it'. But the volts do rise sky high when there is no battery to sink the output - and bulbs/wireless/electronic ignition etc are all then at high risk. The fact this problem disappeared for a while confirms to me it's a bad connection.

Scrap that isolator and replace it with a proper jobbie. The brass type are just pants and this is probably why you are loosing your earth...

Does this mean that isolators are a bit risky? If not, what type would you recommend? MikeN.

This is the type I use and have not had any problems. I mount mine under the dash near the bonnet release so I can reach the switch from inside the car but all the connections are engine side so no heavy cables come through the car...

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Yes - i've had one of this type 'in stock' for about 6 years now waiting to be fitted!
Original 'poster' never came back - so the problem must indeed have been the isolator!

Not suprised if it was ^^^^ I've suffered at the hands of those cheap brass bar type of isolator on a number of occasions

Thanks, PSL. Its about time I got one. MikeN.

No problem Mike. It takes about 10 mins to fit and is a great deterrant as well as a safety device....

Just being 'picky' - but, how is it a deterrant ?

Well maybe not deterrant being the right word, but if there ain't no power to the battery it ain't gonna start. is it?

Yes - but you don't have a big notice saying ' battery isolated to prevent theft ' in the window do you! That would be a deterrant - or maybe would attract theives like flies as they relish the challenge!
Only kidding by the way! It is a usefull anti-theft device. Although - if they bump start the car by getting up enough speed down a hill to get the charging to cut in - then they will still be off with it!