I'm not familiar with the 2.5 but if you're upgrading to an afterglow relay and your car has a transmission amplifier, replace the dedicated gauge temp sender with a dual function temp sender - gauge and afterglow temp sensor. If you don't have a transmission amplifier, there might be a bung just ahead of the thermostat into which you can thread an afterglow temp sensor. The afterglow temp sensor connects to the 5th pin (actually numbered 6) among the small pins in the glow relay.

Sixto
87 300D