As Ron indicated there is a dropper somewhere (I think under the drivers seat) that drops the voltage to 12v for the fule pump.  Any 12v pump will run off the wires that goes to the the original pump.
Gauges are 24v and unique to the 24v systems.
Just in front and below the coil you will find a box with 24v going into it.  This is the reducer for the coil.  The box is just a length of wire that can get hot when on and if you put a multimeter on the output side it will still read 24v but under with the load of the coil in the circuit you will find the voltage in the compete circuit is 10v.  Now normal coils run on 9v (with a ballast) so a normal 12v ballasted coil (such as a Bosch GT 40) will work in place of the original 101 coil (don't as me how I know all this - bitter experience).
On 12v 101s the coil runs on 6v.
On my 101 I had major coil issues and then 24v dissy problems, so I changed my dissy to a 12v electronic bosch version and a GT40 coil with ballast.  I use the switched 24v that originally fed the coil dropper to run a relay that provides 12v direct from my deep cycle battery.  
The electronic ignition improved fuel consumption on gas from 10mpg to 11 mpg but petrol went from 10mpg to 15mpg.  As you will find, that unlike most landies the 101 gives pretty consistent fuel consumption in most circumstances - mainly because it is basically flat to the floor driving in most circumstances.
Garry
				
			 
			
		 
			
				
			
			
				REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101 
1976 Jaguar XJ12C
1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
			
			
		 
	
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