I have recently bought a 1971 XJ6 4.2 litre and I have noticed that the battery instrument dial does not indicate that the battery is charging when the lights are on.

This also occurs when I am idling.

Is this normal or could there be an issue with the alternator?

 

Hi Greeny and welcome.

Best thing to do if you are unsure is to take voltage readings at the battery with a test meter while the engine is running.

 

Thanks Jimbo for the quick and helpful response.

Do you happen to know what the reading should be on the metre when I check it or should it just be a constant

 

You should be looking for around 14.1 - 14.4V with the engine running.

 

As Jim said is spot on.

The S1 alternator is a lazy affair on any day, so the spec is usually at 1500rpm for these older Lucas systems.

From memory again, the alternator on them was about 45amp, so with lights on, and a few other items, the unit is maxing out, and the light will glow.

The S2 alternator was 65amp, and the S3 was 75amp here in OZ, so maybe an upgrade will work wonders. Simple plug and play, not rocket science to fit.

 

Forgot, I do that.

Being an older car, and suffering from "Prince of Darkness" syndrome, I strongly suggest spending a Saturday (or any other day) cleaning EVERY electrical connection, including the numerous earth connections. This will liven everything up significantly, trust me.

Keep that battery fully charged with an external charger. The alternator and battery will luv you.

 

Awesome. Will give that a go. Like the sound of the upgrade though

 

I made a patch cord for my meter to allow it to be connected via the cigar lighter outlet.
I can read voltage in real time under various load and rpm conditions. I found my alternator not guilty and my battery guilty. New battery and all is well.

One of my early lessons was the way to interpret the instrument guage. Slow and numbers a bit questionable. But, it does serve to watch for any big changes. But, wait for it to react. Just fire up the car and watch it slowly get going!!!

Kinda like me nowadays.

Carl

 

Richard,
Preventative maintenance as indicated by Grant will serve you very well, especially for an older car. May I suggest you also look carefully at the driving lights and their sockets.

Clean and tight for all electrical connections is the order of the day.

These few simple tips and some sensible upgrades, as already mentioned, will keep you gremlin free for years to come.

Then you only have to worry about the 'orrible oily bits.

 

Thanks for all your help.