I would put the "new" brake light switch back in, and make sure it is seated properly (no brake lights when at rest). I would then use the procedure to pull all of the codes and see what you have. You could have a sensor problem as well. If it is showing the brake light switch, then you go into hunt mode to figure out if you have a shorted wire.

As a side note, check to see if the cruise works with the two brake light switches (assuming you can start the vehicle). If it doesn't, you still have a problem with the brake light switch or wiring...

You can try to clean the contacts on the old brake light switch, but may not work.


With regard to the test plug:

On 94 and 95 it is under the drivers dash. Behind the crappy cardboard cover. The flash codes tell you which sensor to look at. You have to keep pulling the codes until there aren't anymore. I used it to pin down which sensor was causing me a headache. Then I pulled that sensor and measured resistance. Sensor came up bad. Replaced sensor and problem solved.

As a punishment for figuring it out, I had a different issue occur about a two monthes later. After going through some testing, I am leaning toward the collector ring being the problem. Have to pull it, clean it, and try it out.

 

You may want to get a copy of the electrical troubleshooting manual, as it lays out all of the systems.

Given the history of Lucas electrics, I expected the manual to be thicker...

 

It almost sounds like you have a vacuum leak on the booster for the brakes.