I have another question about my 1996 XJ imported from Canada to the UK. I think I may have a charging problem because the 'Battery' warning light came on on one occasion. No other symptoms, though.

Battery voltage (new battery) is 12.42V. With the engine running it goes up to 14.17V. Alternator must be OK, I thought. Then I loaded the alternator by switching on blower motor and headlights. Voltage fell to 12.33V.

So the question is: does this necessarily indicate a bad alternator? I've seen from reading the forum that bad grounds can cause charging problems, but surely a bad ground would affect the alternator output voltage when there is no load just as much as when there is a load? I would be grateful for any advice/experience members can share.

 

Bad grounds or a bad/dirty connection on the positive side can do it. The voltage drop across a bad connection increases as the current through it increases.

 

I hadn't realised that. Thanks.

 

I agree that you should start with refreshing of grounds. Here's more.
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Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.