Charging Problem: No Battery Light. Excitation Required?

11076 Views 17 Replies 12 Participants Last post by itsonlyme54, Nov 28, 2015

minshum

Discussion Starter · Oct 3, 2010

Sorry about the length of this. I'll try to be concise...

Battery has been good until now. Just had a couple of flats after doing some jobs recently where I had the lights on for a while.

However, after doing a couple of jobs yesterday, I have a charging problem. The jobs were:
1. Boot light switch (bent copper strip into position).
2. Replaced instrument lamps with LEDs (Speedo, Tacho, Odometer)

As usual, on DIY day, the battery was flat. As usual, I bumped it down the drive to fire her up. HOWEVER, on this occasion the alternator didn't seem to have kicked in: a number of warning lights on, no stereo, slow wipers, dim headlights.

First thing this morning, I whipped the LEDs out and put the lamps back in. Then I tried to get a jump start, but when the leads were disconnected, the engine died.

So, I thought as I'd had a few flat batteries after only minor-moderate engine-off use, I'd treat her to a new battery. This fired her up no problem; no warning lights, stereo on, etc. But after a while the battery ran flat. The alternator is only chucking out about 11.9V, so I think this is the next thing to try.

But before I do, there's a couple of things still troubling me:
1. There is no battery light coming on, even stationary with ign on. I've checked the bulb and it is good.
2. I have read about a field excitation signal that is required by some alternators. On some cars this is directly associated with the instrument cluster and as I've been messing, I wondered if this could be a possible cause? Does the alternator require any signals?

Cheers,
Matt

1 - 18 of 18 Posts

dR0Og

· #2 · Oct 3, 2010

Had exactly the same problem on a friends ZR recently. A new alternator solved the problem

ashy

· #3 · Oct 4, 2010

There should be 2 wires to the alternator. One is the output to the battery, the other is the sense wire from the ignition. This is a circuit via the battery lamp. If you replace it with a LED the circuit can't be completed and hence no ouptut from the alternator and also no lamp.

minshum

Discussion Starter · #4 · Oct 4, 2010

Thanks both. Ashy, I didn't replace the battery warning light with an LED, only the clocks and odometer, but I've taken 'em back out now anyway.

The ZS has a fuse (#24, 15A I think) that supplies the excitation and warning light, but I can't find anything on the ZR. I think I'll go and check every fuse, just in case. I did pop the boot light/radio fuse at the wkd when I fixed the boot switch and plugged the bulb back in. That was pretty weird in itself. Boot light works fine now though.

starlight14

· #5 · Oct 4, 2010

the 11.9 volts were did you check this ie battery post or alternator. Check the voltage each side of the 140amp fuse because the fuse bolts become slack.

minshum

Discussion Starter · #6 · Oct 4, 2010

starlight14 said:
the 11.9 volts were did you check this ie battery post or alternator. Check the voltage each side of the 140amp fuse because the fuse bolts become slack.

Checked at both battery and alternator stud. Is that fuse between the two? If so, it rules that out then.
I have checked every fuse under the column and in the engine compartment (incl. the 140/150A), which was a real ba**-ache, but they're all good. No, not back-ache.

Car is at the garage having a new alternator, but I still have a bad feeling.
It's just too much of a co-incidence for me having the cluster out. I don't know whether the battery light was working before or not.

hampo1989

· #7 · Oct 4, 2010

This happened to me this morning... half way round a round-about... and nothing! everything stopped. i ended up getting towed to work! New battery, not charging! so replacing the alternator tomorrow.

ashy

· #8 · Oct 4, 2010

minshum said:
Checked at both battery and alternator stud. Is that fuse between the two? If so, it rules that out then.
I have checked every fuse under the column and in the engine compartment (incl. the 140/150A), which was a real ba**-ache, but they're all good. No, not back-ache.
Car is at the garage having a new alternator, but I still have a bad feeling.
It's just too much of a co-incidence for me having the cluster out. I don't know whether the battery light was working before or not.

Just put 12v to the sense wire. If the alternator is working it should start charging when the engine is started.

starchild

· #9 · Oct 4, 2010

Some years ago I had a very similar problem with my Nova SR and what had happened was that one of the tracks on the circuit board thingy behind the clocks had become damaged after I replaced the speedo cable, replaced this and problem sorted!!

minshum

Discussion Starter · #10 · Oct 6, 2010

Alternator Ruled Out

Alternator was replaced today. But, just as I suspected, to no avail.
Auto-electrician dropping into garage tomorrow. I suggested the same as you Ashy - to bypass everything and stick +ve directly onto the sense wire. Fingers crossed!
Hampo, how did you get on?
Starchild, I have read about these hairline fractures in the tracks at the back of the instrument cluster. I belled out the ones that went to the battery light and could measure the diode at the connector (diode test drops 0.56V as you'd expect). It may be one of the other tracks.
Is it worth me getting a Haynes manual? I've heard there's no wiring schematics in there, which surprises me.

starchild

· #11 · Oct 7, 2010

minshum said:
Is it worth me getting a Haynes manual? I've heard there's no wiring schematics in there, which surprises me.

They are fairly useful, but there is not much in there about wiring, there is a website that I used last year to get wiring diagrams for my ZS and my MGF, can't remember the address at the moment but pretty sure it is a German site.

forehead

· #12 · Oct 7, 2010

Just so people aware a good battery should show around 12.6v across the terminals with engine off. Repeat this with engine running and you should see between 13.5 and 14.5v indicating a healthy alternator.

Funny how people assume cars run at 12v when they can been running at over 14v

minshum

Discussion Starter · #13 · Nov 3, 2010

Problem solved a few days later but only just got around to posting!
There is a 2-pin plug on the alternator. These two connections were, in-turn, shorted to pos and neg, which seemed to reset something (perhaps in the ECU)? The battery light now comes on, when iginition in position II and it's charging a treat.
So, it looks like I didn't need to spend >£200 on new battery and alternator afterall. Just need to temporarily link out this exciter signal.
Hope this helps someone out there!

Jotte

· #14 · Apr 23, 2011

I have had the alternator out to change the rear bearing, however the one who did this forgot to connect the connector again and it was melted on the exhaust. Now I soldered wires directly on the alternator, however it is not charging, I was wondering if anyone could tell me where the stripe wires goes when seen from front of engine? Also I do not have a fuse diagram, if anyone would be so kind as to tell me what fuses to check I would be greatful!

Thanks in advance, Jon

boonergooner

· #15 · Jun 9, 2013

minshum said:
Problem solved a few days later but only just got around to posting!
There is a 2-pin plug on the alternator. These two connections were, in-turn, shorted to pos and neg, which seemed to reset something (perhaps in the ECU)? The battery light now comes on, when iginition in position II and it's charging a treat.
So, it looks like I didn't need to spend >£200 on new battery and alternator afterall. Just need to temporarily link out this exciter signal.
Hope this helps someone out there!

How do you do this?
"These two connections were, in-turn, shorted to pos and neg, which seemed to reset something (perhaps in the ECU)? The battery light now comes on, when iginition in position II and it's charging a treat"

Cheers.

dfx

· #16 · Jun 13, 2013

boonergooner said:
How do you do this?
"These two connections were, in-turn, shorted to pos and neg, which seemed to reset something (perhaps in the ECU)? The battery light now comes on, when iginition in position II and it's charging a treat"

Cheers.

I didn't understand that, either. My problem is :
. Battery flat was flat after little use.
. Recharged, then days later after a 5 mile trip, battery flat.
. Recharged whole night, mesured 12.5v next day, started car, 13.5v showing.
. After 20minutes drive battery warning light came on, strange never happened before.
. Battery light went off and stayed off after 2 minutes.
. Got home and noticed 2 things : battery light does not come on before the engine is started, battery voltage only showing 12.1v

Could I have the same problem? How do you fix it?

z0ool

· #17 · Nov 10, 2015

im having the same problem, i have run 12v to the sense wire and get the light on but still not charging (well battery was flat this morning)

http://forums.mg-rover.org/showthread.php?t=794297

itsonlyme54

· #18 · Nov 28, 2015

ashy said:
Just put 12v to the sense wire. If the alternator is working it should start charging when the engine is started.

I have a similar problem, I am running mems3 and would like to try putting a feed to the sense wire, of the two small wires to the alternator which one do I connect the live to ?

1 - 18 of 18 Posts

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