Cadillac Repair: 1984 eldorado, cruise miles, eldorado biarritz

Question
I have a 1984 eldorado biarritz convertible. I am having problems with the electrical. The car was running rough and a local mechanic said it was an injector wire. Replaced it an it still had intermittent problems. He said it was the computer. Replaced it. It runs fine but now the service now light stays on and cruise, miles to empty, and other dash elctronics not working. Any ideas?

Answer
OK, Let's get the codes from the computers.

1. Turn ignition ON. Do NOT start engine.

2. Simultaneously push and hold the OFF and WARMER buttons on your climate control panel for 3 seconds and release them.

3. Tell me everything that displays on the display until you see the .7.0 or the word ECM and then turn OFF the ignition key.