The manual says the red lightning bolt warning light on the dash should go out after about 20sec after the engine starts.

If it stays on, what does it mean? What are the symptoms and consequences of the red lighting bolt warning light?

 

As I recall (been a few years since I had an XJS) the lightening bolt warning lamps = "charging system over voltage".

Cheers
DD

 

If the charging system is over voltage it will boil your battery effectively killing it.

You need to measure the voltage to determine what the problem is.

Charging voltage should be no more then 14.4volts, if it is then your alternator is faulty and will need to be repaired/replaced.

 

Besides likely incurring additional damage to the battery, if the engine starts and purrs nicely and all other indicators are within acceptable range, is there a danger in driving the car with the lightning bolt warning lamp being on?

 

Can't say without knowing the voltage. Serious over-voltage can indeed cause system damage. I don't think I'd be comfortable with more than 15v. Warrjon will know if the danger point is higher than that

Cheers
DD

 

This light will come on when there is a charging problem, so it could be low or high voltage.

I would NOT drive the car until I know what the problem is. If the voltage is high, over 14.8v you run the risk of the battery leaking at best exploding at the worst.

Charging voltage should be between about 13.5 to 14.4 volts. Over 14.4volts or under 13 volts I would suspect a problem with the regulator in the alternator.

Also DO NOT disconnect the battery with the car running, this can cause spikes and kill other electronics in the car especially the ECU.

 

I'm not so sure! But, I might be getting the warning icons mixed up.

There are two warning lights associated with the charging system.

First is the conventional 'battery' or 'alternator' warning light that operates via the exciter wire....as we see on virtually every car on the road. As I recall the icon is a battery.

Then there's the "over voltage" light ...which is triggered by the "over voltage sending unit". I think this has the lightening bolt icon.

Cheers
DD

PS- in your opinion how high must voltage be before things start frying? Instruments, blowers, ECU, bulbs, etc?

 

Any references or ideas?