Window switch VS tach accuracy..

[triggz]

I know that the stock tach is known to be off by even a few hundred RPMs, but I'm worried my window switch is reading inaccurately as well.

I'm running a PEP tach adapter with a Mallory #646 digital window switch. I have a shift light hooked up to it to turn on from 3k to 5.7k (testing for nitrous). The adapters green light is on indicating it is wired properly.

Now the problem is, the light comes on at around 2600rpm, I haven't had a chance to go WOT and test the top end, but I'm sure its off as well. The light also flickers when the car bogs down to the 400rpm range.. so if it werent for the WOT switch it would spray at idle

Has anyone else had problems with the window switch reading off? Can wire length or gauge effect the signal? I extended the tach signal wire from the adapter by about 6' to reach the switch.

 

[DBMSTNG]

do the odometer trick where you hold in the reset button then start the car. hold the button for 15 seconds and you'll see different stuff appear on your odometer. one of them is a digital tach. it's about as accurate as you can get. check that against the other tachs to see if one is off.