Tachometer woes...

[Des]

I was participating in a similar topic in the 240 tech forum and thought I'd try here for a bit more help.

I have a 96' 240SX SE with approximately 110000 miles on it. Two suspect things I've had done recently were an aftermarket radio install which required bypassing the factory amps and an oil change.

About 2 days ago, I noticed my tach was not moving beyond 3.5k rpm as I shifted through the gears. However, acceleration and speedometer readings felt and looked perfectly normal.

The next morning my tach would not move beyond the 2k rpm mark but within about 10-15 min of driving we were back at around 3.5k again.

Being less mechanically inclined than I'd like to admit, the only thing I've done thus far was make sure the wires were connected securely behind the guages.

What are your suggestions?