Hi all
'82 XJ-S H.E. v12 automatic. 7700 original miles, recently acquired, working through all the things you would usually have to do on a car that has been very rarely used.
I guess it's time I addressed my charging issue. Admittedly, I've done nothing yet but tighten up the alternator belt so far.
Starts and runs great. Lightning bolt light not on. Battery light on when it starts but soon goes out. Dash gauge shows approximately 12.6 volts initially, typically hovers just into the "off charge" zone when driving and sometimes just into the "charge" side after driving for a while (all around the 13 volt mark).
A voltmeter on the battery shows 12.6 when the car is off. Here's the weird part to me: it shows a consistent 14.0 when idling with no extra loads turned on, but does not increase when revved to 1500-2000. With lights, high beams, brake lights and wipers on, it gives 13.4 or so off the battery.

I know I should clean up the connections on the alternator, and check grounds everywhere, but in the meantime does this seem indicate if a specific issue? Diodes or regulator?

Thanks!
Peter

 

Peter,

On the face of it, I don't think you've got an issue at all. On a well-charged battery, the alternator will only output to about 14.1 at the battery, so your figure seems ok. Try measuring your voltage bot at the alternator output, and also at the +ve and -ve posts on the bulkhead. You might find it's fractionally higher there, and consider disconnecting and cleaning up those bulkhead points. You might be losing a fraction from there back to the battery in the boot.

Cheers

Paul

 

Thanks for the quick response, Paul! I've had the battery go dead, hence my thinking there is an issue, but I definitely haven't tested enough. Into the garage tomorrow ...

 

I agree with Paul.

Instrument cluster Earth issues are rife, and simply sorted, see my attachment.

I would systematically go around the car, beer in hand, and clean and lube ALL the earth connections you can find.
Alongside the battery, Engine Earth Strap Fiasco at the LH engine mount, are the 2 main culprits for weird stuff.

Any aftermarket alarms, etc, are also top of that battery drain list.