1996 Olds 88 tach wire

I'm installing a remote starter/keyless/alarm unit on my 1996 olds 88.

I have the door locks working, and  the starter is almost working. I have not been able to find the tach wire to hook that into the remote starter, and I believe this is the cause of the problem.

When I start via the remote, the starts up, but only runs for a few seconds. It also cranks the starter for a long time, about 10 seconds. I believe this is because it's not getting any feedback from the tach wire telling it the engine is running.

So, I need help finding the wire. the vehicle wiring description here on 12volt says it is a PURPLE / white wire behind right side of dash, I assume below glove box? There are several boxes there, and one has a PURPLE / white wire, but as I underatand it, I should be able to measure an AC voltage on this when the vehicle is running, that varies with RPM.  I get a small DC voltage on this line but no AC.

The insturment cluster itself doesn't have a tach, but I assume they would still have run the line in. 

Can anyone point me in the right direction here? Where is the engine control computer, which I believe would have the tach going into it.

Thanks