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Mpi Charging Issue.

electrical

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#1 Volcano98

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Posted 08 December 2023 - 02:00 AM

Hi people, new to this great site after reading many posts. I have a 98 mpi cooper s works.
Due to my own error when changing the 12 yr old battery I accidentally had the batt the wrong way round in the dark(plonker) & both terminals connected for a brief moment . This resulted in me frying the alternator because the charging light stayed on thereafter and indicator's stopped working. Found a 10a fuse blown which when replaced got the indicators back on.
New alternator fitted but have charging problem:
In a nutshell…
New batt & new 65A Alternator.
Ignition On- batt light is On .
Engine On - batt light goes out ( as normal).
Multimeter on Alternator b+ to Alternator body (engine on) 16.3v.
Multimeter at batt (engine on) = 12.1v
Multimeter at batt (engine off cold) =12.6v
Voltmeter on dash now reads around 12v ( was reading around 14v before)
Engine starts fine.
Why is alternator overcharging .
I’ve read about the fuseable links near alternator. Could I have fried this when I originally connected batt wrong way and would this cause this . I would have thought I’d have a batt light on if this was blown though ?
Any help much Appreciated.

#2 Midas Mk1

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Posted 08 December 2023 - 08:21 AM

There is an inline fuesable link from the alternator to the starter, using your multimeter you can do a continuity test to see if this has been triggered.

Easy and quick to test, live on alternator to starter main 12v with the engine off

#3 Midas Mk1

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Posted 08 December 2023 - 08:27 AM

16v charging is too high too, i'd be wanting to check the voltage regulator.

#4 bpirie1000

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Posted 08 December 2023 - 10:04 AM

I would suggest checking the earth between the block and the body usually under the left hand side of the engine under the engine steady.

Buger to get to on mpi as you have to remove the breather.

Noting stopping you putting one in a different place.

Short term try using a jump lead from the engine block and the good ground on the body.

Then check your charging voltage..

#5 Volcano98

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Posted 08 December 2023 - 04:25 PM

So, took grill off and immediately noticed that the ring connector at the end of the fuse able link that attaches to the starter solenoid had broken off/corroded. Cut off 5mm of corroded wire and re connected . Checked continuity to alternater and the fuseable link itself had not blown.
Engine on- hey presto ! Back to charging over 14v .
Many thanks for suggestions people.

#6 cal844

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Posted 08 December 2023 - 05:14 PM

So, took grill off and immediately noticed that the ring connector at the end of the fuse able link that attaches to the starter solenoid had broken off/corroded. Cut off 5mm of corroded wire and re connected . Checked continuity to alternater and the fuseable link itself had not blown.
Engine on- hey presto ! Back to charging over 14v .
Many thanks for suggestions people.


Nice cheap fix, well done and thanks for letting us know the fault





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