Check engine codes with no engine light

How would I check the engine codes if I have a 4.0L 87 XJ with no trouble lights at all? So the turning key on and off thing won't work. Is there something under the hood that I could hook up a small 12V light to to get a flash or what???
Any help would be great.

Thank you

nope, sorry but the Renix injection system (87-90) does not store any codes.

What are you trying to figure out? The XJ/MJ didn't have DTC's until 1991, and the RENIX system doesn't seem to have anything go wrong with it very often... Most of the tests can be done with a DVM, and you can get the RENIX FI manual by downloading it from strokers (groups.yahoo.com/group/strokers) - you'll have to join, but it's free (and informative!)

5-90
1987XJ, 1988XJ, 1989XJ, ...