Fluctuating battery charge and instrument light

[notsofast]

Five days ago I got in my M49 as it was getting dark, and noticed that the fuel gauge needle was glowing with faint pulses of light.  Odd, I thought, not noticed that before. Anyway, the engine fired up normally and I drove 2 journeys of about 13 miles each way. The needle glow was also there before firing up for the second journey.  The next day I tested the battery with a multimeter, it measured 12.67 volts, so perfectly normal.  Two days later I tested again, the charge had dropped slightly to 12.53, but that's what I'd expect over 2 cold days of not being driven.  Also I couldn't see any glowing on the fuel gauge needle (though it was daylight, which would make it hard to see).   But then I looked again tonight, after dark, and again I could see the the needle is pulsing faintly.  So I tested the battery again, and the really odd thing is, the reading on the multimeter had gone up, to 12.68, though I hadn't driven the vehicle nor charged the battery.  Can anyone shed light on what might be happening?  The battery is about a year old.

[Multispacer]

Five days ago I got in my M49 as it was getting dark, and noticed that the fuel gauge needle was glowing with faint pulses of light.  Odd, I thought, not noticed that before. Anyway, the engine fired up normally and I drove 2 journeys of about 13 miles each way. The needle glow was also there before firing up for the second journey.  The next day I tested the battery with a multimeter, it measured 12.67 volts, so perfectly normal.  Two days later I tested again, the charge had dropped slightly to 12.53, but that's what I'd expect over 2 cold days of not being driven.  Also I couldn't see any glowing on the fuel gauge needle (though it was daylight, which would make it hard to see).   But then I looked again tonight, after dark, and again I could see the the needle is pulsing faintly.  So I tested the battery again, and the really odd thing is, the reading on the multimeter had gone up, to 12.68, though I hadn't driven the vehicle nor charged the battery.  Can anyone shed light on what might be happening?  The battery is about a year old.

I think you may be chasing a battery fault that isn't there. As your battery is only a year old and from your post you didn't seem to have any problems starting/driving the van and you haven't mentioned anything else not working and battery voltage not actually fluctuating that much, I would think the problem lies elsewhere.

The thing I would look for [and these can be quite hard to trace] is a ground fault. A ground fault on a system, caused by a corroded/oxidized earth point can cause small standing voltages to be fed to systems that are normally not powered and cause things like your dim illumination on the fuel gauge seen when the vehicle is not powered up. Given the age of your M49 [2001] that is probably quite likely.

[notsofast]

Thanks. I think my leading post gave the wrong impression that I thought the battery was at fault, and what you say tallies with what I had read online generally about loose or corroded earths (though they had usually said the battery earth might be at fault).  What I am curious about is the fact the battery charge has gone up - I had expected the charge to drop more quickly than normal if something is taking power when it shouldn't.  I suppose the multimeter might not be totally accurate, or is it possible that the fault you mention could result in a wayward reading?

Regarding your analysis of a faulty earth, is there a best place where I should start my search - the fuses? I'm guessing it might be trial and error - i.e. find a wire that looks badly connected, clean it up and see if that works?

P.S. The only other thing that might be worth mentioning is the fact that the bearings in the alternator belt tensioner are getting worn, so the belt is a little noisy when running.  I can't think why this should cause the needle glow, but this is the only 'anomaly' within the electrical system that I was previously aware of.

[Multispacer]

Thanks. I think my leading post gave the wrong impression that I thought the battery was at fault, and what you say tallies with what I had read online generally about loose or corroded earths (though they had usually said the battery earth might be at fault).  What I am curious about is the fact the battery charge has gone up - I had expected the charge to drop more quickly than normal if something is taking power when it shouldn't.  I suppose the multimeter might not be totally accurate, or is it possible that the fault you mention could result in a wayward reading?

Regarding your analysis of a faulty earth, is there a best place where I should start my search - the fuses? I'm guessing it might be trial and error - i.e. find a wire that looks badly connected, clean it up and see if that works?

P.S. The only other thing that might be worth mentioning is the fact that the bearings in the alternator belt tensioner are getting worn, so the belt is a little noisy when running.  I can't think why this should cause the needle glow, but this is the only 'anomaly' within the electrical system that I was previously aware of.

As I stated earth faults can be quite tricky to track down, as the high resistance earth could be at any of the many earth points. They're not always obvious [ie not always visibly corroded] sometime they might just be oxidized.

What to arm yourself with, some electrical contact cleaner spray [to spray on any earth point you do clean up prior to refitting] and your multimeter along with another long lead with crocodile clips on each end to use in conjunction with your meter. You might also need a second person to observe the voltages on the multimeter. The reason for the extra cable being so you can get to all the remote earth points [including inside the vehicle] by attaching it to the negative probe of the multimeter.

A fairly good video [short and from a UK based source] to watch to give you an idea of how to go about it is here:

https://youtu.be/Swz_LSU4-pk?feature=shared

As the guy says, anything more than 0.4V difference and that earth point is suspect.

[notsofast]

Thanks for the info and video link. Once the weather warms a bit I'll have to do some investigating. Fortunately it's not a major issue and the battery charge today (12.41 volts) was more what I'd expect on a vehicle not being driven every day (i.e. the charge dropping slowly over several days - not going back up again like it seemed to be before).

[Multispacer]

Thanks for the info and video link. Once the weather warms a bit I'll have to do some investigating. Fortunately it's not a major issue and the battery charge today (12.41 volts) was more what I'd expect on a vehicle not being driven every day (i.e. the charge dropping slowly over several days - not going back up again like it seemed to be before).

One thing I should have added in my previous reply, in that when you attach a longer extension to the negative probe of your multimeter to check earth points that might be remote, such as in the vehicle cabin, first check across the battery again and take that reading down, as with a longer lead there will be a different voltage reading [due to the voltage drop caused by the inherent resistance on the longer cable] and as you are only looking for a relatively small voltage drop, you want a good starting reference point.

[notsofast]

Thanks. Yes, that's a good point. I only really became conscious of the effects of resistance last year, when I used a 25-metre extension cable for a professional pressure washer, and a fuse blew.  I had used the cable several times before with no ill-effect, so it might have been exacerbated in this case by the cable looping back on itself a bit in a couple of places.  Now I use a 15-metre cable, to be on the safe side.