Need Help w/ 8-pin Diagnostic Module

[Cal Learner]

I've done this many times in the past without problems, but suddenly I can't seem to get the 8-pin diagnostic module (X92) to work right. This is a Calif version with push button and red LED. (1988 260E with 103 motor.)

KOEO, hold the button 2-4 seconds and read the pulses. One pulse means everything's OK, no stored codes. But today, the red LED shows a steady light as soon as the key is turned on, and no amount of holding the button causes the LED to flash or to go off. Why is the LED on continuously, and how do I get it to turn off so that I can perform the pulse tests?

[mbdoc]

Does the ABS light stay on as well?

Possibly a problem with the over voltage protection relay

[Cal Learner]

The ABS light is not on, except briefly as it's supposed to when the key is turned on. Otherwise, no ABS light and the ABS seems to be working fine. OVP was replaced (upgraded 2-fuse version) 4 years (23K miles) ago.