I was thinking about adding some aftermarket gauges to my 2000 bonneville...i want to put a transaxle temp. gauge and i was wondering if anyone knew how the sending unit installs.

I just did this. It'* a real bitch. There'* a Techinfo article (link at the top of the page) but it'* not totally specific to your application. Alot depends on the type of sending unit you use.

Mine is a thermocouple with the Ether-charged tube to the gauge. My gauge is mounted in an A-pillar pod.

On top of your transaxle, right below the TB and crossover pipe heat shield, you'll see a little hex 1/8NPT plug. This is the pressure test plug. I have a series of brass fittings in that hole to adapt to my thermocouple, and the ether tube routed through the firewall.

This is a very smart mod. The trans is the weak spot in the drivetrain.

Welcome to the Club!