M-Series Circuit Numbers

American M-Series military vehicles follow a common system of electrical circuit numbers. This simplifies maintenance procedures and training of military mechanics who have to work on many different vehicles. In some cases it allows common parts to be used for multiple applications.

M-3 tank engine wiring harness manufacture at Chrysler, World War II
M-3 tank engine wiring harness manufacture at Chrysler, World War II.

For a more complete listing of military standard circuit numbers than the table on this page, consult this file based on TACOM's Ordnance Drawing 7070301 [285k PDF download].

Today in WW II: 14 Jan 1943 Churchill and Roosevelt begin the Casablanca conference.   

M-Series Military Vehicles Circuit Numbers

M-Series Military Vehicles Circuit Number Wire Tag

Every electrical line in the vehicle will have small metal tags crimped around the wire near every junction or connector. The metal tag will bear a number and that number uniquely identifies what electrical circuit the wire is carrying. All wiring is black so the metal tags are the only ID for you to use, unlike color-coded commercial vehicle wiring.

Electrical components, such as switches, recepticles, and lights may also have the same identifying numbers. If they come with pigtails, there will probably be a tag on each wire. If they just have a socket, the circuit number may be part of the housing or painted on. If you make any changes to your vehicle wiring, try to preserve the wire tags and to properly tag anything you add. That will help you or the next owner when the time comes to try to understand what you did. If you can stamp military style metal tags, great. If not, use other wire label methods but use the correct numbers.

In order to help you when you service your vehicle or make any changes to its wiring, here is the list of numbers. The information on this list was compiled from PS Magazine, #38 (1955) and TM 9-8000 Principles of Automotive Vehicles (1956). No one vehicle has all of these circuits and most wheeled vehicles use only a small subset of them.

Related information is available on Olive-Drab in the article about the wiring of the M-Series Light Switch and turn indicators.

Note that not all numbers are used; if a number is skipped in the table, it is unassigned. If you find any error in this table, please contact Olive-Drab.com.

Wire Number Circuit Description
1 Generator field circuit (main feed)
2 Generator armature circuit (main positive line)
2A Alternator field, to 5A terminal on alternator
3 Generator ground circuit
3B Alternator ground circuit
4 Generator regulator to ammeter or shunt
5 Ammeter or shunt to starter terminal block or battery connection
5A Battery positive to alternator main feed
6 Battery to starter
7 Battery ground including master switch if in this circuit
8 Shunt to ammeter positive
9 Shunt to ammeter negative
10 Ammeter or shunt feed to instrument panel circuit breakers
11 Ignition switch feed or magneto ground (LH)
12 Ignition switch to ignition coil or booster switch to booster coil
13 Magneto ground (RH)
14 Starter switch circuit (including feed) to relay or solonoid
15 Main light switch feed
16 Light switch (HT) to service headlamp or dimmer switch
17 Dimmer switch to high beam service lamps
18 Dimmer switch to low beam service lamps
19 Light switch (BOD) to blackout driving lamp including resistor
20 Light switch (BHT) to blackout marker lamps
21 Light switch (HT) to service tail lamp
22 Light switch (S) to service stop lamp
22-460 Turn signal switch to right rear stop lamp
22-461 Turn signal switch to left rear stop lamp
23 Light switch (BS) to blackout stop lamp
24 Light switch (BHT) to blackout tail lamp
25 Horn switch (including feed) to horn or horn relay
26 Horn relay feed and horn relay to horn
27 Instruments feed (instruments with polarity)
28 Fuel indicator to sending unit if single tank, or left upper tank indicator to selector switch
29 Fuel selector switch to right upper tank
30 Fuel selector switch to left lower tank
31 Fuel selector switch to right lower tank
32 Oil level sending unit to indicator or selector switch
33 Water and oil temperature indicator to sending unit
34 Low engine oil pressure warning light circuit, including feed
35 High water temperature warning light circuit, including feed
36 Oil pressure indicator to sending unit
37 Outlet socket
38 Dome light circuit, including breaker and switch
39 Map light circuit
40 Instrument light circuit
41 Interphone #1
42 Interphone #2
43 Interphone #3
44 Interphone #4
45 Interphone #5
46 12 Volt radio circuit, including radio master switch
47 Slip ring feed
48 24 volt radio feed
49 Receptacle, aux power outlet, positive lead
50 Receptacle, aux power outlet, negative lead
51 Interphone #7
52 6 volt tap on tail light dropping resistor to tail light
53 Electric brake control circuit
54 Fuel cut-off circuit
55 Flame primer low tension circuit
56 Flame primer high tension circuit
57 Instrument panel ground
58 Compass light circuit
58E Voltmeter ground
59 Hull ventilating fan circuit
60 Interphone #6 (extra)
61 Auxiliary generator field
62 Auxiliary generator armature (positive line)
63 Auxiliary generator ground
64 Auxiliary generator regulator to battery, including heater transfer switch
65 Auxiliary generator starter relay circuit, including switch and feed
66 Auxiliary generator starter to transfer switch, including starter or relay
67 Emergency stop switch ground
68 Battery interconnecting cables
69 Resistor to ground terminal on trailer coupling
70 Regulator ground (LH)
71 Windshield wiper circuit
72 Low transmission oil pressure indicator circuit, with feed (LH)
73 Radio terminal box to ground
74 Starter solonoid circuit (actuating) including switch or relay
75 Stop switch circuit (SW to SS on main light switch)
76 Fuel pump control feed
77 Fuel pump switch to fuel pump left
77B Fuel pump safety cut-out switch (??)
78 Fuel pump switch to fuel pump right
79 Fuel tank ground
80 Ignition coil to distributor
81 Battery positive feed to starting motor terminal block, including master switch
82 Starter motor terminal block to starter motor, left
83 Main light switch (TT) to tail light connection on trailer receptacle
84 Main light switch (SS) to stop light connection on trailer receptacle
85 Low air pressure indicator light
86 Ground on series parallel switch, to ammeter, including circuit breaker
87 Spotlight circuit for trucks and wreckers
88 Winch torque limited control
89 Automatic choke
90 Trailer receptacle to ground
91 Headlamp to ground
92 Parking lamp to ground
93 Starter relay grounding circuit
94 Starter relay auxiliary grounding circuit
95 Tail lamp to ground
96 Speedometer sending unit feed
97 Tachometer sending unit feed
98 Interphone #8
99 Interphone #9
Wire Number Circuit Description
100 Turret feed
101 Impulse relay feed (L terminal on impulse relay)
102 Large cal. gun firing solenoid to impulse relay (S terminal)
103 Small cal. gun firing solenoid to firing switch
104 Traverse motor feed
105 Recoil circuit on gyro control, through recoil switch
106 Gyro control (#3 on an connector) to motor stabilizer control, yellow post
107 Gyro control (#1 on an connector) to motor stabilizer control, green post
108 Stiffness circuit including disengage switch
109 Gyro stab. switch feed including circuit breaker and switch to gyro motor or anti-backlash switch
110 Gun firing and lights, circuit breaker feed
111 Gun firing switch, feed from circuit breaker including safety switch
112 Gun firing safety switch indicator light
113 Firing switch to large gun firing solenoid or impulse relay (F terminal)
114 Gyro control resistors feed
115 Firing relay feed
116 Gyro indicator light feed
117 Positive lead to gun firing switches
119 Normally open side of anti-backlash switch, to circuit #107
120 Normally closed side of anti-backlash switch to gyro control resistors feed
121 Junction of circuits #114 and 120 to gyro motor feed
122 Firing switch to loaders safety relay
123 Loaders safety relay to shell primer
124 Firing switches to selector switch
125 Feed to loaders trip button
126 Loaders trip button to feed on test relay
127 Test relay to loaders safety relay coil
128 Loaders trip button through loaders setting button to controlled side of test relay
129 Loaders ready to fire indicator circuit
130 6.5 inch selector light
132 Ammunition hoist circuit
133 Parallel disconnect circuit
137 Outlet socket
138 Dome lamp, spot light and reel circuit
141 Interphone #1
142 Interphone #2
143 Interphone #3
144 Interphone #4
145 Interphone #5
146 12 Volt radio circuit
147 Light for periscope and sighting devices
148 24 Volt radio feed
149 Commanders master control circuit
151 Interphone #7
152 Commanders master control circuit feed
154 Rammer motor control circuit, including switch and indicator
155 Elevating motor feed through circuit breaker and main switch and indicator ligh
156 Brake solenoid feed through brake relay
157 Elevating lead from reversing relay to elevating depressing motor
158 Depressing lead from reversing relay to delevating depressing motor
159 Turret vent fan
160 Interphone #6 (extra when used)
161 Feed for elevating and depressing control mechanism through circuit breaker
162 Elevating relay control through control switch and limit switch
163 Depressing relay control through control switch and limit switch
164 Brake relay control through brake switch and ground
165 Elevating and depressing relay mechanism to ground
166 Automatic elevation control through resistor and limit switch
167 Automatic depressing control through resistor and limit switch
168 Equilibrator motor feed including switch and indicator light
169 Gun, How. firing area control circuit
173 Radio terminal box to ground
174 Rammer control circuit
198 Interphone #8
199 Interphone #9
Wire Number Circuit Description
201 Generator field circuit
202 Generator armature circuit
203 Generator ground circuit
204 Generator regulator to ammeter or shunt
211 Right hand ignition switch feed
212 Right hand ignition switch RH coil
214 Starter switch or relay feed circuit
233 Temperature gauge to sending unit
234 Oil pressure pilot light
235 Water temperature pilot light
236 Oil pressure gauge to sending unit
255 Flame primer low tension circuit
256 Flame primer high tension circuit
267 Emergency stop switch
270 Regulator ground right hand
272 Transmission oil pressure pilot circuit light
274 Starter solenoid circuit right
280 Ignition coil to distributor
282 Starter motor feed right hand
293 Starter relay grounding circuit
294 Starter relay auxiliary grounding circuit
Wire Number Circuit Description
300 Air pressure gauge to sending unit
301 Ignition switch to throttle solenoid through feed terminal in terminal box
302 Throttle solenoid to throttle out switch (H)
303 Throttle out switch to brake throttle switch (A)
304 Feed terminal in terminal box to feed on clutch switch (D) and normal range switch (E)
305 Normal range switch to low range (F) and high switches (G)
306 High range switch on low/high range shift to switch on high/normal range shift switch (K)
307 Switch on high/normal range feeding direct solenoid and converter solenoid
311 Brake governor switch (C) joining 312 to low side of governor
312 Convertor solenoid to brake governor switch (C)
313 Common lead on brake governor switches to high side of governor
314 Brake governor switch (B) to direct solenoid
315 Low range switch (F) on low/high range shift to high range solenoid
316 High range solenoid ground
317 Clutch switch (D) to clutch solenoid
318 Clutch solenoid to clutch solenoid ground switch (J) on converter direct shift
319 Common side of throttle cutoff switch and clutch grounding switch to grounding terminal on terminal box
320 Brake throttle switch to grounding terminal on terminal box
321 Transmission lube pressure gauge circuit
324 Transmission temperature gauge circuit
325 Red flasher light with switch indicator and flasher
326 Differential low oil pressure warning light
327 Transmission high oil temperature warning light
329 Feed to transmission and steering control
330 Transmission high range control
331 Transmission low range control
332 Transmission reverse range control
333 Transmission clutch lockup control
334 Steer control right
335 Steer control left
336 Converter low oil pressure
337 Pilot control indicator circuit
338 Co-pilot control indicator circuit
339 Converter low lubricating oil pressure
340 Speed selector switches feed, pilot
341 Steer selector switches feed, pilot
342 Speed selector switches feed, co-pilot
343 Steer selector switches feed, co-pilot
344 Inlet fan, right
345 Inlet fan, left
346 Circulating fan, right
347 Circulating fan, left
Wire Number Circuit Description
400 Heater feed
401 Heater starting switch to coil and indicator light
402 Heater starting switch to pump and solenoid valve
403 Running switch to thermal switch
404 Thermal switch to heater starting switch
405 Heater starting switch to motor and indicator light if used
406 Heater ignition circuit and indicator light if used
407 Heater in operating position indicator circuit
408 Oil heater circuit including indicator
409 Compartment heater circuit, including control unit
410 Safety valve reset circuit
411 Ventilation fan lead
412 Auxiliary generator transfer switch to battery heater and indicator
413 Heater relay control circuit
414 Auxiliary generator voltage control reostat to voltage regulator
415 Feed to special ventilating fan or rotoclone
416 Ground lead for special ventilating fan or rotoclone
417 Auxiliary shunt to auxiliary ammeter positive
418 Auxiliary shunt to auxiliary ammeter negative
419 Main feed to auxiliary control box
420 Auxiliary engine oil pressure gauge circuit
421 Auxiliary engine fuel cut off valve
422 Auxiliary engine magneto ground
423 Signal lamp auxiliary interphone
424 Field telephone auxiliary interphone
425 Field telephone auxiliary interphone
426 Ground auxiliary interphone
427 Tachometer, electric, "A" terminal, send to receive
428 Tachometer, electric, "B" terminal, send to receive
429 Tachometer, electric, "C" terminal, send to receive
430 Tachometer, electric, "D" terminal, send to receive
431 Speedometer, electric, "A" terminal, send to receive
432 Speedometer, electric, "B" terminal, send to receive
433 Speedometer, electric, "C" terminal, send to receive
434 Speedometer, electric, "D" terminal, send to receive
435 Rear door emergency warning light
436 Comp. feed including relay
437 Comp. relay control circuit including switch
450 Bilge pump switches feed and jumper between switches
451 Bilge pump switch to rear bilge pump
452 Bilge pump switch to front bilge pump
453 Ignition retard circuit, starter to solenoid through normally closed switch
454 Ignition retard circuit, battery to normally open side of switch
455 Two speed generator control circuit
456 Auxiliary generator disconnect control circuit including the switch
457 Interphone #10
458 Engine fan clutch circuit
459 Control circuit for master relay and indicator light
459B Master relay feed
460 Turn indicator circuit, right, front signal/marker lights
461 Turn indicator circuit, left, front signal/marker lights
462 Generator equalizer circuit, shunt type
463 Interphone #11
464 Interphone #12
465 Range finder feed
466 Range finder ground lead
467 Light switch to turn indicator switch feed
468 Bulldozer actuator armature feed
469 Bulldozer actuator field and clutch feed
470 Bulldozer control solenoid valve circuit
471 Winch control switch feed
472 Winch reverse solenoid circuit
473 Winch forward solenoid circuit
474 Front end fuel tank solenoid
475 Rear end fuel tank solenoid
476 Transmission fan clutch circuit
477 Differential filter pressure circuit
478 Generator equalizer circuit, interpole type
478A Auxiliary generator equalizer circuit
478M Main generator equalizer circuit
479 Battery heater control circuit
480 Wrecker solenoid valve control circuit
481 Magneto switch feed
482 Feed to auxiliary engine magneto grounding relay
483 Turn indicator, right blackout light
484 Turn indicator, left blackout light
485 Cab feed
486 Manifold heater, main engine
487 Manifold heater, auxiliary engine
488 Rectifier control to master relay circuit
489 Clearance lamp service feed
490 Clearance lamp blackout feed
491 Parking lights to light switch
492 Ignition ground, ground mag. switch
493 Auxiliary generator temperature indicator circuit
494 Engine decompression control circuit
495 Transmission oil level gauge circuit
496 Flood or spot lamp ground
497 Red flasher ground
Wire Number Circuit Description
500 Three phase circuit lead "A"
501 Three phase circuit lead "B"
502 Three phase circuit lead "C"
503 Motor generator/alternator feed
504 Motor generator/alternator ground
505 Motor generator/alternator control box feed
506 Generator charge indicator circuit, left or main engine
507 Generator charge indicator circuit, right engine
508 Generator charge indicator circuit, auxiliary engine
509 Warning light circuit, selective warning system
511 Battery heater feed, from engine generator to series paralleling switch
512 Battery heater feed, battery heaters in parallel
513 Battery heater feed, battery heaters in series
514 Dimmer switch to blackout upper beam (IR)
515 Dimmer switch to blackout lower beam (IR)
516 Power pack feed (IR)
517 Periscope feed (IR)
518 Flood or work lamp feed
519 High beam indicator circuit
520 Main light switch to IR BOD selector
550 Power feed to pulsing relay box
551 Traverse lead between cont. potentiometer wiper and relay contacts
552 Traverse center tap on cont. handle potentiometer to deat spot res.
553 Elevation center tap on cont. handle potentiometer to deat spot res.
554 Elevation lead between cont. potentiometer wiper and relay contacts
555 Common ground in pulsing relay system
567A Voltmeter from ignition switch
568 Alternator field from ignition switch
Wire Number Circuit Description
600 Elevation tracking motor feed
601 Tracking motor elevating circuit
602 Tracking motor depressing circuit
603 Elevation gyro gauge circuit
604 Elevation gyro motor and pickoff motor feed
605 Elevating electrodyne feed
606 Elevating electrodyne circuit
607 Depressing electrodyne circuit
608 Traverse tracking motor feed
609 Tracking motor left traversing circuit
610 Tracking motor right traversing circuit
611 Traverse gyro gauge circuit
612 Traverse gyro motor and pickoff motor feed
613 Left traversing electrodyne circuit
614 Right traversing electrodyne circuit
615 Traversing electrodyne feed
616 Hydraulic valve circuit
617 Loaders traverse safety lamp feed
618 Delay relay coil circuit
619 Thermo delay switch actuating circuit
620 Delay relay holding circuit
621 Gunners handle pickoff motor feed
622 Commanders handle pickoff motor feed
623 Commanders override circuit
624 Commanders override switch feed
625 Main positive feed to turret control box
630 Delay circuit feed
631 Safety lamp return
632 Loaders safety switch and safety lamp feed
633 Loaders safety relay coil circuit
640 Auxiliary generator decompression circuit
641 Booster motor control
642 Booster motor power
643 Inverter feed
644 Inverter ground
645 Turret relay control circuit
Wire Number Circuit Description