I don't know what you are trying to do.
If the switch in question is off of the machine you are working on, please post the model and serial number of the machine so we can search online for a wiring diagram.
If you are trying to "match up" a different switch to a different machine it may end up being necessary to know both machines identity.
Generically:
"B" is for the input from the battery source'
"R" is typically to indicate "red wire" out to components that need 12V power in the RUN position of switch (Cub to name one).
"S" indicates starter control out.
"L" can indicate lights if lights function is part of the key switch duties (may have other functions on different machines.
"A" might be used to power accessory components in some applications and may or not be a separate position from RUN on the switch. On some applications "A" is simply an additional output to lessen the total load on other outputs of the switch.
Typically on some applications you might also find these letters:
"G" (ground), provides for a separate ground wire to the switch body in applications where the switch is mounted in a nonmetallic panel.
"M" (magneto), is found in applications where the key switch functions to kill the ignition spark by shunting the magneto primary wire (kill wire) to ground when the key is turn OFF.

Not totally sure, but I think the R was used for older battery/points type ignition systems.

Thank you for the explanation mownie, that's what I wanted to know. Very helpful!

On my subero 2004 outbake what are the colors of the wires and aere do thsy go . i dont have the

I'm working on a 1983 John Deere 820 rear tine tiller. It has an unserviceable 4 terminal key switch. Letters are G, B, S, D.......I figure Ground, Battery, Start......but what the heck does the "D" represent?

Any help appreciated. john

Not sure what the D stands for I'm trying to figure that out as well if you can help

I am replacing an ignition switch on a rascal mobility scooter the existing switch has the bat,ign,and acc on the terminals the new one has 1 ,11,and111 on the terminals are the corresponding terminals ,any help much appreciated