1978 ? thunderbolt 500 50 hp wireing help !!!!!!!!!!!!!!

[dustin6213]

i have a i belive 1978 mercury thunderbolt 500 50 hp i am rewireing the key switch it is a steering wheel model i found this diagram online but cant seem to understand what the white wire goes to for start and on can anyone explain this better

 

[haventaclue]

That diagram is not for a '78,it's this one https://maxrules.com/oldmercs/Wiring/1966ona/500_76_78eL.jpg Post your outboard number to pinpoint year of motor
The white wire is the 12V+ to tach and choke.When the key is in the run/start positions,the 12v passes from terminal A(red) to F(white).On other motors that use the Merccontrol,there is a white wire from the engine to the plug F terminal

 

[dustin6213]

That diagram is not for a '78,it's this one https://maxrules.com/oldmercs/Wiring/1966ona/500_76_78eL.jpg Post your outboard number to pinpoint year of motor
The white wire is the 12V+ to tach and choke.When the key is in the run/start positions,the 12v passes from terminal A(red) to F(white).On other motors that use the Merccontrol,there is a white wire from the engine to the plug F terminal

the serial # is 4078181 cant seem to find a model number on it but it is a 500 thunderbolt 50 hp

 

[dustin6213]

also i dont have ignition colis it goes off a distributer looking thing like in the diagram i posted but the one you posted matches my wires

 

[haventaclue]

In that case your motor is 1974 ,this might be the right diagram which is the same as the one you posted. https://maxrules.com/oldmercs/Wiring/1966ona/26A.jpg

 

[haventaclue]

Or this one https://maxrules.com/oldmercs/Wiring/1966ona/28.jpg The white goes all the way to the switch box