I saved some of the thread I talked about that pertained to my car.
It states:"The example I will use is an 88 560sel a/c system as that is what started this whole thing.
locate x11/4 connector(on the firewall near mono valve)
Plug the black connector in #1 and the red into#7,with the key "on" touch the exposed end of the wire to ground for three seconds and release.the led will blink any where from 1 to 57 times.
One blink means no fault,if it blinks more than once write it down
check for the next code,keep doing this until the first code is repeated.
Touch and hold the wire to ground for seven seconds to erase codes.
Instead of listing all the different codes on this forum I recommend that anyone intrested in using this tool order the DIAGNOSTIC TROUBLE CODE REFERENCE GUIDE through M.B. publishing."
Would not this fellow's 87 420 have the same circuits as 88 560? Please advise if they are different or am I confused as the above quotation refers to AC codes??? If I was confused I want to apologize to Jherrera for the advise I gave.