It took me two tries to resolder the K40 module in my '96.

After I soldered the big leads to the board, it worked great for a couple of weeks, then failed again. Resoldering the big leads let the relays "float" a bit on the board and stressed the small (control) leads. These small leads then developed cracks at the solder joints.

I resoldered the whole thing again, first the big ones, let it cool, then the small ones. It has worked since then.

If it quits, the first step for me will be a new K40 module as it is not expensive and very easy to change. The next step is the ignition switch.

If the K40 is not powering the engine computer and DAS is installed on your car, the lamps on the mirror will alternate, and the engine will not start. This also happens if you lock the car from the outside, then try to start the engine.