'97 2500 Diesel Tachometer/Brake Lt Issues

[Fasteddy51]

I have a '97 Chevy 2500 Ext Cab long bed that I am having troubles with. It has a diesel engine and I am having troubles with the tachometer and the brake lights. I don't think the issues are related, although they both started about the same time. The RPM guage needle goes way up and stays there, although the engine obviously runs fine and operates as normal. The brake lights also do not work now, and I have checked the obvious, bulbs, rear circuit board continuity, etc. I also appears that there is not a switch under the dash that is like some of the earlier versions that have a plunger on the back side of the brake pedal. I have also checked the fuses, and also the master cylinder/ABS unit to see if there is a pressure switch that might be bad? Anyone have any ideas? I am getting frustrated trying to figure these problems out at the same time. Any info would be greatly appreciated.