Assuming EP82 and assuming your mounting the rpm gauge (rev counter/tacho) on the dash somewhere then one of the easiest places to run the wire from is to pop the factory gauge cluster out and run the wire from there. Its the white 12pin connector that fits into the back of the gauge cluster. Looking from the wire side with the latch on top its the 6th wire in from the right, should be white (but they can vary). Other place to run from is the engine loom to dash plug next to the steering column. Forget which pin but its normally a black wire sometimes with either white dashes or brown dashes.