I had the same problem with a 16 degree day after a 70 dgree day here in Wyoming. Battery wouldn't start the Disco '99 and ALL the lights came on and stayed on so after I finally got it started, all lights went off except the blinking green M and S lights. I bought a charger for $44.00 at Advance Auto after they read 9.2 volts (and saying it would be fine because he doesn't know what we're dealing with) and charged the battery overnight and I fired it up next day and all lights went off. Except the battery light. However, after driving a half block, the battery light went off and now I have ZERO dratted warning lights on. Thanks a million!

 

I'm having the same flashing M&S lights. I tested the battery and the voltage is perfect both running and off.
I've heard that this issue could be due to a bad Crank Position Sensor or something called an XYZ (neutral safety or transmission position indicator) switch.
Is there any way to tell for sure? I'm trying to avoid a massively expensive repair and replacing parts that won't fix anything.

 

Did you test the battery/alternator under load? Meaning every electric gizmo on, as possible, and check for voltage?

 

No, however there is no "load" on the vehicle when the lights are flashing either. I'm showing high 12s volts with the car off and mid 14s volts with it running. According to what I've read, the trans components have an issue at 9V. I'm no where close to that.

 

OK, Just wanted to make sure you are covering all the bases before replacing other items. Flashing M&S is 99% of the time an electrical issue in my experience.

 

Are planning to do the work yourself or have a shop work on it which may be expensive. Good used x,y,z switches are less than a hundred bucks and there a small possibility just a minor adj of switch could fix it.
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Oh how I Wish it was that easy! I guess I could check voltages (and grounds) at the components in question. Any idea where I should look?
Do you have any guidance on the "small possibility just a minor adj of switch could fix it"?

 

The adj would probably only work if you are not getting correct shift selector indications. Is that one of your symptoms too?

Below is the R&R of the switch. It has two mounting bolt which when loosened a bit allow a small rotational adjustment. You would adj in hopes of getting correct indications.
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It won't shift out of first gear, and when I try to use the selector to pick a different one, the light stays flashing on the "D" setting. Not sure if that is what you are referring to or not.

 

Lever moves but won't change gears while driving? There are illuminated indicators on selector lever for P, R, N, D, 3, 2, & 1 and a dash LCD indication of position. When selector moves the indications should correspond to it's position.

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