Volvo Repair: Overdrive light and check engine light dimly lit on 91 740, fuse panel, knock sensor

Question
The overdrive light on my mom's '91 740 intermittently comes on.  The check engine light came on dimly with the overdrive dimly lit.  Mom fiddled with the overdrive button (which is her natural reaction to lights coming on).  Normally this makes the overdrive light return to normal indications-on when overdrive off, off when overdrive on.  We read the trouble codes-got a knock sensor code 143.  Cleared the codes and now no check engine lights.  Also, now have no idiot lights during key in on position just prior to start.

Answer
it could be a problem in the electrical part of the ignition switch for the no lights with key in posisiton one.the overdrive light coming on may be may be a bad overdrive relay.

the overdrive relay is located on the fuse panel behind the ashtray.remove the ashtray and then remove trim around lighter socket then you will see 2 screws remove the screws and the storage area will come out the relay is white and about 1x1x3  inch.it will be towards the passengers side of the panel.