Trying to install Dynotune window switch

Ok so I am getting a little frustrated with this install. I have everything installed and programmed the digital window switch. It is setup to come on when TPS voltage reads 4.7v and 3-6k rpms. When I try and activate it I only get about a one second busrt of nitrous before it shuts off. Acording to Dynotune it is because my tach signal is noisy and they told me to buy a tach adapter from MSD. I think that was kind of a crappy answer and it seems there should be a way to make this work. The tach in my car works fine. So I have tried the negative side of the coil and the back of the gauge cluster, but no luck. I am trying to find a concrete answer as to which wire on the ECU is tach signal. I have a 94 Cobra, but I am not sure if its the same as the GT's.

Can anyone help me out?

Thats the link to my window switch. I tried the tan wire off the coil. Mine is tan and I can find any yellow on it what so ever. I even traced it behind the dash on my tach and still no yellow. Supposedly it goes to pin 48 on the ECU, but looked and can say with 100% certainty that pin 48 on my ECU is white and purple.

When I use the tan wire and check the reading on the box it just jumps around from 1k-2k rpm. This is why the dynotune guy is telling me my signal is noisy. The signal is more stable when I tap in behind the dash though. Is it possible that my condensor is bad?

http://www.dynotunenitrous.com/store/scripts/prodView.asp?idproduct=194

I connected mine to the signal wire on the TPS also and it worked fine. I cant remember which wire it was though. I can check and post back later. I do not have a MSD box, and now its more a matter of making it work because its supposed to. I like the idea of how its works and makes things nice a safe. I am really tempted to just through my microswitch on there and call it a day.