Make a turn, "BRAKE" warning/indicator light comes on
 

I have a 1990. When I make a left or right turn, about 50% of the time, the red "Brake" warning light comes on. Most of the time, it'll go off after about two minutes. Sometimes, it'll stay on until I make another turn, regardless of the direction. I've checked the fluid level (obviously) and it's right on. I shouldn't overfill, right?

Hopefully I'm not overlooking anything obvious. I searched the forum and didn't find anything. Any ideas?

My best guess, not knowing where you are.

The fluid container on a '90 is, I think, mounted direct on top of the master cylinder????. If so then the float is jamming, or the switch contacts in the cap itself are grubby.

Remove the cap, spray the contact area inside the cap with "Brake Clean" and test with a meter for contact integrity, you may sort it that simply.

IF yours is the "remote" container, then the float most certainly will be jamming, as it is a cork float inside a thing alloy tube. VERY common.

Brake warning light
 

FWIW, replacing the OEM container with one from a Mitsubishi is cheap and easy. It uses a magnetic float which is more reliable than the Jaguar piece of cork. Plus it doesn't let air in like the OEM part, which means your brake fluid won't look like syrup so soon and you won't need to bleed the brakes as often.

You can get the reservoir online for under $40, and new hoses can be found at the local hardware store (air line hose) for not too much.

John
1987 XJ-S V12
63,000 miles

Thanks for the ideas, folks. I'll check it out and see how it goes. Much appreciated!