Unusual speedometer gear housing
 

Just started working on a customer's 72' Bonneville. The car is very original with it's 455-2 bbl engine and long shaft turbo 400 transmission. Found it has this speedometer housing with a wire going to it, along with the traditional speedometer cable. Is this a speedometer speed warning option? I've never seen one in 40 years of working on Pontiacs.

That is the transmission controlled spark speed sensor. It works in combination with the solenoid on the intake and temperature sensors on the engine to keep vacuum advance off of the distributor under 25MPH or not above a certain temperature\warmed up (the temp changed year to year from 1971-1974). 1972 only thing on transmissions from GM cars.

Well, that's a new one for me! Never heard of that before. Learned something new!