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Battery Light Queerness


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Monday evening coming home from work, the battery light came on in the TD5. Thing is, it would go out when I let off the gas and also, sometimes whilst idling stationary. 

Once home, I left it for ~24 hours before utilising my extremely limited electrical experience!

  • Rested battery 13v
  • idling no load 14.6v
  • idling w/load 14.5v

Dodgy regulator, and overcharging?

I'm clueless with electrics!


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Hi, I'm no electrical wizard either but the voltages look good to me in as much as the alternator is charging. Is the drive belt ok and not slipping? My thinking is that the light goes off when you take the power off. Can you check the water in the battery in case it's boiled off which might mean over charging.

The more knowlegable will be along soon.


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I replaced the belt and tensioner less than 6 months ago, so they should be fine. There's certainly no obvious signs that the belt is slipping.

Will check the battery water - thanks. Other thing I did notice is there is quite a build up of corrosion on the positive terminal and I do believe I've read that this can be a sign of over charging too?


Edit: thanks for the links

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Following Escapes suggestion, likely sticking brushes, especially if the car has been offroad/wading in the past. I don't know the td5 at all (or what style alternator is fitted to it), but often the brush pack can be removed as an assembly without even taking the alternator out. Clean it up and make sure the brushes move freely - or just change it while you're in there.

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I had chance to have a little poke around at the weekend - battery water level was fine, no immediately obvious signs of dirty, bad connections (from what I could see without removing stuff). The alternator on the TD5 is a pig to get to, I imagine removing brushes in situ would be very difficult, if at all possible.

There was however evidence of a slight coolant leak near the belt idler (previously I bodged a small length of pipe to replace the bend of that small bore plastic pipe that always breaks where it joins the rad, which no doubt was the culprit). My thinking was could coolant be making its way onto the belt causing it to slip? It made sense as the light had only come on once engine had been at operating temp (cooling system under pressure), however if belt was slipping wouldnt I feel heavy steering from PAS pump not turning?

I ran engine up to temp in the hope that I could observe leak and it's projection, except there was no leak. I went for a quick drive, no battery light, still no leak. belt slip idea absndoned. I decided to use car for work today.

Light came on briefly on the way to work, and on the way home. Both times whilst doing ~70mph on a dual carriageway.

Is there a clue in that I wonder? 

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Update! There may be a diagnosis of sorts!

Coming home from work on Friday the light came on and stayed on. It was on when I switched off, so I thought I'd grab my multimeter straightaway and test whilst the light was present. Only it wouldn't start! So definitely the alternator as fault and not the warning light!

Took alternator off and it's very oily/dirty. Seems the culprit is the front camshaft cover, so will be replacing this before I go any further.

Brushes were well and truly gunked up (see photo - was worse than that but a lot of crud fell inout upon removal). Now, I'm thinking there is a very good chance that the dirty brushes could have been sticking or just not making contact, which would explain the intermittent fault? How likely does this sound?

I've cleaned them up, but am I wasting my time refitting them and the alternator? 




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