One handy little gadget that was optional on 1974 through 1978 full sized Chrysler and Dodge cars is the Fuel Pacer System. The Fuel Pacer was just another attempt to help the driver of the car save fuel. When the driver is accellerating away from a stop or passing on the highway etc. the fuel Pacer will light up the left fender mounted turn signal indicator to signal that the driver has crossed that line between poor fuel economy to atrocious fuel economy.
The Fuel Pacer is simply a vacuum guage or more accurately a vacuum switch. The switch will close at or below about 3 to 5 inches of manifold vacuum causing the left fender mounted turn signal indicator to light up, and it is adjustable. I believe the adjustment procedure is in the FSM. (this light has become known as the "money light" among some of my friends)
I happened to have a spare Fuel Pacer that I got from a salvage yard at some point and I recently decided to install it in my 1977 New Yorker Brougham.
You can see the installed Fuel Pacer fastened to the left inner fender well just ahead of the Cruise Control assembly.
There are three wires that are connected to the Fuel Pacer. Well, there are actually two but there are three connections to be made. The two black ones go to the indicator light wire just outboard of the battery.
After you disconnect the flexable intake duct (if your car is so equiped), find the black connector in the cavity outboard of the battery.
Run the two cylindrical connectors from the Fuel Pacer down to where the signal indicator connector is.
Disconnect the signal indicator connector.
Plug the lamp side of the signal indicator wire into the matching plug coming from the Fuel Pacer.
Plug the other wire that comes from the fuel Pacer into the remaining wire that formerly fed the signal indicator.
Run a vacuum line from the Fuel Pacer over to the vacuum tree on the intake manifold near the rear left of the carburetor.
The one remaining wire from the Fuel Pacer must be connected to a power source that is live only when the ignition switch is on the ON or Acc positions. This will be the power that lights the signal indicator when you mash the throttle. I'll have more specifics and pictures about that connection soon.