M38's initially had circuit protection only for the lighting, horn, instruments, and the aux pwr receptacle on the firewall.
Wire 10 from the regulator fed the bottom CB then was piggy backed to the middle and top CB's then that feed delivered unprotected voltage to the ignition switch power lead 11. The lower CB protected the aux power receptacle on the firewall. The middle CB protected the power feed 10/15 to the light switch and the top CB protected the power feed 25 to the horn.
Then a seperate CB on the instrument cluster recieved power from the 27 wire off the ignition switch and protected the oil pressure, water temp and fuel quantity circuits.
At serial MC65042 the instrument power CB on the cluster was deleted.
At serial MC65927 the three CB's on the cowl battery box were deleted.
Do not confuse the MWO that moved the bottom CB with a circuitry change. It was only moved because too many folks were kicking it when trying to kick the starter button.
M38's from serial MC65927 and on and all the M38A1's and M170's had NO circuit protection.
The military thinking here is the CB is the weakest link and when in a hostile environment they did not want to loose a tactical vehicle because the CB failed or stuck open.
This is the late manual diagram.
This early manual diagram shows the wiring much clearer and keep in mind that this wiring diagram applied to 80% of M38 production. Don't confuse the wire running from the regulator and piggy backing across each breaker and then going to the ignition switch as a protected wire. It is not. It is hot all the way from the regulator.
This is clear in this diagram.
Note: the full size photos of these diagram are available on my photo storage site:
http://willysmc.mypicgallery.com/
