27 replies to this topic

[OlivierW2]

Hello,

 

A few weeks ago, I had a problem: my battery wasn't getting charged when the engine was running. So, I changed the alternator.

It turns out the problem was maybe not the alternator.

 

After starting my Mini, the battery lamp in the dashboard doesn't turn off.

 

When my ignition switch is on the second position or when the engine is running, I don't have 12V on the "D+" terminal of the alternator, I just have a few volts (fluctuating).

 

So, due to the problem mentionned above, I also don't have any voltage on the "B+" terminal.

 

What I have tried: I've disconnected and isolated the "D+" wire. I have then connected a 12V motorcycle battery to the "D+" terminal of the alternator and the ground of the battery to the ground of the car.

Then I've started the engine.

Result: the brand new alternator is giving something around 14V!

 

But, the voltmeter in my Mini still reads around 12V. And when I measured the battery, it is still around 12,6V.

So, it is not charging.

 

Sounds like I have a wiring problem between the engine bay and the battery.

 

I've been told the wire between the "B+" terminal and the starter motor could be corroded, as it is a common problem. I haven't been able to check it, yet.

 

What else can I check?

Is it a common problem?

 

Do you think I may need to replace the whole wire(s) between the engine bay en boot? If so, is it doable without a car lift?

 

Thanks in advance for all your help!
Olivier

[bpirie1000]

Check the earth wire under the engine mount.

Try a jump lead from engine to a good earth.

Corrosion is a pain.. also worth checking the ring terminals on the starter solenoid.

Also prone to corrosion.

[NLinPEN]

My recommendation would be to inspect the entire circuit. Usually the cables from the alternator to the battery themselves are not the problem. But their connectors can have developed corrosion.

And then there is the return path via ground. Here old cars more often are suffering from issues caused by corrosion. Make sure that the ground cable from the battery is properly connected to the car body. Then, in the engine bay, make sure that the alternator makes properly electrical grounding contact. This is not a separate cable, but the metal housing of the alternator needs to have good contact with the engine and car body.

[nicklouse]

Have you changed any dash bulbs?

[OlivierW2]

Check the earth wire under the engine mount.

Try a jump lead from engine to a good earth.

Corrosion is a pain.. also worth checking the ring terminals on the starter solenoid.

Also prone to corrosion.

 

Thanks a lot! I haven't found the earth wire you are talking about. Is it under the car? I can't safely lift it at the moment.

But I have checked with a voltmeter and everything seems to be properly grounded around the engine bay. A few years ago I had a earth problem in the boot, between the battery and the body, but I had solved it and the problem isn't present anymore.

 

Anyway, you are right, the problem is the corrosion, around the starter solenoid. (More info at the end of my post)

 

 

 

My recommendation would be to inspect the entire circuit. Usually the cables from the alternator to the battery themselves are not the problem. But their connectors can have developed corrosion.

And then there is the return path via ground. Here old cars more often are suffering from issues caused by corrosion. Make sure that the ground cable from the battery is properly connected to the car body. Then, in the engine bay, make sure that the alternator makes properly electrical grounding contact. This is not a separate cable, but the metal housing of the alternator needs to have good contact with the engine and car body.

 

Thank you for your answer! I've fgound the problem, and in my case it's the wire, not the connector. I admit I'm not sure how the wire cut itself, because it's quite protected and doesn't seem to move much. Also, I'm never driving in the rain, same for the previous owner.

 

You are right, like I answered to bpirie1000, a few years ago, I had the problem between the battery and the body. I checked again today, but it's still fine!

Same with the alternator, I checked its body was grounded properly to the engine, to the car's body and others earth point.

 

 

Have you changed any dash bulbs?

 

No. And AFAIK, all the dash bulbs are originals. Or at least they have never been changed with LED bulbs. I had read that using LED bulbs in the dashboard, especially for the battery lamp, would cause problems.

 

 

 

So, I found the problem. I started the engine, and the battery was still not charging. Then I moved a bit some random wires, especially those near the starter motor, the alternator and the ECU. And suddenly, the Mini voltmeter started measuring above 13V! And the dashnoard battery lamp switched off.

 

By checking directly the battery with my voltmeter, it was finally somewhere around 14V! 🤩

 

Then I moved again the wires a bit, and the voltmeter started showing around 12V, again. After wiggling the wires some more, I found the problem was very close to the solenoid.

 

At the end, I found the exact wire: it was in a very poor condition, and finally broke on its own (see my attached pics, in red is where the wire is going).
First picture, everything looks alright. Second picture, the wire is completely broken.

The wire was going in a soft tube, then this tube is taped to some corrugated plastic tubes.

 

 

 

This wire is between the "B+" and "D+" wires, in size. So, I'm not sure where it comes from.

Can I just directly add a wire between "B+" of the alternator? Or "D+"? Or something else?

Or does it go through a fuse?

 

On the wiring diagram for the MPI, there's "hypalon fusible cable", going from the alternator to the starter motor. Is it this cable?

 

What's the best way for a permanent fix?

Thanks again for all your help!

Attached Files

•  1.jpg   61.02K   0 downloads
•  2.jpg   45.75K   0 downloads

[NLinPEN]

Well done! Finding a broken wire is not always an obvious task.

I can't comment on the actual wire because I do not have an MPI car myself. Instead of replacing the wire, would it be possible to reconnect both broken ends together?

[OlivierW2]

Yes, the good thing is it was not in an unreachable place. And I was lucky to have my father with me: it's easier to be two persons: one wiggling the wires, and the other checking the voltmeter

 

The other part of the wire is inside the soft tube. Anyway, this wire is totally unsafe: the part that you can see in the second picture is brittle and will break sooner or later. I really need a new wire.

 

Tomorrow I'll disconnect the wires connected to the alternator, and will check if one of them is connected to the wire still in the tube.

[bpirie1000]

Well done, glad to have helped and this is why the forum is such a good resource.

Would also suggest that sponsoring the forum and making a subscription would pay for the knowledge/diagnostic time..

[tmsmini]

It looks like that is one of the fusible links. You need to replace it with an appropriate replacement fusible link. I have sources in the US, but hopefully someone will provide a UK source

[OlivierW2]

Well done, glad to have helped and this is why the forum is such a good resource.

Would also suggest that sponsoring the forum and making a subscription would pay for the knowledge/diagnostic time..

 

You're right, members have helped me quite a few times, I've just subscribed! Thanks again to all the members of this great forum! ✨

 

 

It looks like that is one of the fusible links. You need to replace it with an appropriate replacement fusible link. I have sources in the US, but hopefully someone will provide a UK source

 

I'm in France, so I probably won't order from the USA, but I'm interested in a reference. Or you can send me a link by private message if it's not allowed to share here.

 

What is a "fusible link"? And where should it be installed?

 

 

I've removed the protection of the wire and I've been able to check that the broken wire is attached to the large one going to the "B+" of the alternator.

Any idea why the large wire doesn't directly goes to the starter motor? Why was there a smaller wire (which broke)?

On an original Mini MPI, is it the same wiring than mine? Or was it "fixed" by someone else in the past?

 

I have tried to remove the heat shrink where the large wire connects to the thinner one, but it seems like it's glued. Is is also normal?

 

Thanks again for all your help!

Attached Files

•  3.jpg   47.02K   1 downloads

[NLinPEN]

About your question: "what is a fusible link?"

I assume that you are familiar with the fuse box in your car. The fuses are components that you place in this box. A fusible link does the same function. It is a piece of thin metal wire which has to melt when the electrical current is too high. So it looks like a wire but has the same function as a fuse.

Therefore you cannot replace it with any random piece of wire as that won't have the current protection feature.

If you can't find a replacement for this fusible link you could replace it with a regular wire and an inline fuse. If you go this route you have to be careful to protect the inline fuse from the harsh environment (temperature, humidity, dirt, etc).

I hope this helps.

[OlivierW2]

Thanks a lot for your answer, NLinPEN! Yes, of course, I know what regular fuses are. And one of the first thing I did, was to check all the normal fuses were fine: the four 30A ones in the engine bay, and the multiple others fuses on the right side, inside the car.

 

OK, now I understand. So, the wire which broke on my Mini is the fusible link? How am I supposed to know its value? As I mentionned in a previous message, the wiring diagram for the MPI mention a "hypalon fusible cable", but without giving the value.

 

The broken wire on my car is in poor state: I can't read anything on it (if something was written in the past).

[OlivierW2]

So, after searching, I've found out I need a 4 gauges smaller (or higher, I feel "AWG" is weird…) fusible link than the rest of the cable. That means, if my cable going from the alternator, to the starter motor is 12 AWG, I would need a 16 AWG fusible link.

 

Tomorrow I'll go check the size of the cable connected to the alternator, hoping it's written on it. I'll report back.

 

Anyway, I still have a problem: I have found 2 websites in the USA which sells fusible links. But I'm in France, and would prefer to buy from Europe or the UK. Why is it so difficult to find this fusible links?

 

Or, like said by NLinPEN, I may replace it by an inline fuse.

Edited by OlivierW2, 16 April 2026 - 09:50 PM.

[Designer]

Hi,

 

This posting on the forum on the 30/01/2014 might be of some help

 

Spi/mpi Fusible Links & Alternator Wiring

sorry don't know how to post the link.

 

Paddy

[NLinPEN]

Hi,

 

This posting on the forum on the 30/01/2014 might be of some help

 

Spi/mpi Fusible Links & Alternator Wiring

sorry don't know how to post the link.

 

Paddy

https://www.theminif...+fusible +links

That is indeed a good reference for this discussion.