Battery Warning Light on?

[R.Edgar]

Any advice will be most welcome.
'88 5.3
Battery failed while out driving at the weekend resulting in a 'jump start'.
Charged the battery and now the battery light remains on. It had shown previously but I tensioned the belt and all seemed OK.
Now the Battery Light is on all the time.
The Alternator is putting out 14.4v and the battery is showing 13.10v. When the ignition is off the battery shows 12.78v
???

Roger

[poprivet]

Bosch alternator, possibly the load dump module? small box near the alternator with a wire going into it. Could just be a bad earth/connection.

[Brakebuster]

this is the one screwed to the inner wing with a single black wire

BB

[oldtimer]

Now, there's interesting !

What is a load dump module - what is it's function ?

One black wire - must be earth

Is this unique to Bosch ?

[R.Edgar]

Bosch alternator, possibly the load dump module? small box near the alternator with a wire going into it. Could just be a bad earth/connection.

Spot-on, Bosch Alternator.
Forgive my ignorance but what shape is the unit I need to find?

[poprivet]

A very common fault on XJS and XJ40 of this age, it contains Zenner diodes and a common failure is to provide a leakage to earth hence the flat battery even with a functioning alternator. Have a google for information, although I've never had one go myself,

Like BB says, it is a small box screwed to the body (which provides the earth) and a single wire going to the alternator.

[R.Edgar]

Found the module, tapped it, no change.
However when I switched the ignition on, about the 3rd time, the battery light went off within 3 seconds or so. Started the engine and the light remains off.
Alternator reading 14.3v and the battery 13.4v, with the engine running.
Googled the part in question, very interesting reading so far. Mine does not have any connector only the black wire to the small pin on the alternator.
Thank you for your input Guys.