Is it the battery or the alternator that's at fault?

[Robert Stirrat]

>I switched on the the dips again without any decrease in brightness.  The
>car's voltmeter was reading just over 12 volts.

......................indicating the voltage is due to alternator
functioning. The battery itself would probably show a voltage of less than
12 volts. The alternator provides over 13 volts to the circuit, which is
what charges the battery.



>So It's fairly evident that I've got a problem with either my battery or
>charging circuit.  I removed the battery for charging only to find that the
>electrolyte was a murky brown colour and all levels where low in each cell.

......................not an encouraging discovery. The battery is doomed.
You have evidence of a failing battery, regardless of the condition of the
alternator, so fix the battery and try again.

Ok, I hope to do this tonight weather permitting (it's blowing a gale here
in
the West of Scotland with speeds upto 100mph).  I just hope I don't need to
wrestle with the alternator too.

>I topped up the levels and charged the battery for 8 hours at 2 amps.  I
put
>the battery back in the car not before removing all the white crud from the
>battery tray. Exactly the same symptoms occurred, again with the voltmeter
>displaying a little over 12 volts.

................again, alternator functioning properly. Batteries don't
make over 12 volts.

Are you sure? Don't they read appx 13 volts unloaded?


>It looks like my battery is on it's last legs, I take it the discoloured
>electrolyte is internal corrosion of the plates?  AM I right?

.............agreement, or someone added some "dope."

I don't think the car could be bothered starting at all if a dope additive
was in there!

>  I've still to
>try measuring the voltage drop across the battery terminals to check if the
>alternators is providing a charge.

.......................do it with the engine off. Then, the alternator
isn't doing anything and the only source of voltage is the battery.

>   Though wouldn't this give the same
>reading as the cars voltmeter?

....................see above.

Gotcha, I'll do this before I do anything else.

>Any help, hints, tips or advice in solving this would be much appreciated.

.................put in a fresh battery and then test the system. And
consider that the headlight switch may be badly cooked from years of use,
and may be offering additional high resistance due to carbonization of the
contacts. The plastic holding the contacts gets so hot that it melts and
flows. This happens over and over for years, and eventually the plastic
breaks down and oxidizes into lots of other compounds and elements,
including carbon. You may have to replace the switch, or possibly several
switches. I suppose there is a switch on the dash and a switch on the
steering column. My experience has been with a 4kq and a 5ktq, not the
coupe.             Doyt


Thanks for taking the time to write such an informative reply, I let you
know my findings when I try your suggestions.

Kind regards,
             Robert.