Help please! Just purchased it a few weeks ago and have this CODE 12 by using the "key trick"...It seems as if I had disconnected the battery before every startup because the clock reads 12:00 and none of the radio stations are set. And sometimes is hesitant, and others fires right up. I want to get this beast on the road ASAP!! Thanks

 

Check all your grounds, a known problem with XJ's. Start with the major ones off the battery and the battery too.

 

Simple stuff first. Always. Get your battery "load tested". Any parts store will do this for you for free. The fact that you're losing your presets indicates low available battery voltage.

And freshen/clean all battery connections until they are shiny! And I also agree that you should freshen all grounds as MtnHermit mentioned.
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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.

 

Thank you. I will check all grounds and the battery first thing tomorrow morning and let y'all know the outcome.