Spreadsheet for wiring K series engine into MG Midget or MGB

 In K Series Conversion, MGA-MGB, Midget
Paul Walbran Motors:   Wiring notes, K series engine & ECU intalled into MG Midget
(This was done for a VVC, but is generally applicable to non-VVC which is the same except for the VVC-specific sensors and functions)
Note:  For this project, we used a standard MGF VVC ECU, the alarm ECU originally fitted to the same car as the donor engine ECU, the engine loom from an MGF,
and the matching plugs from the main loom of an MGF which connected it to the engine loom.  We also used the diagnostic socket from the donor main loom.
The main ECU plugs are of the early 36 pin type
Part 1 of this spreadsheet attempts to diagramatically show the layout of where the various componets branch off the looms
Part 2 lists the functions of the various individual wires and includes some additional tips and comments
Part 3 is the business end – it is the list of connections to make in order to blend the VVC loom to the original MG loom.  You may like to skip the explanations and go straight to the connection summary in this section
(Although developed for a Midget, it should apply equally to the MGB as the components and colour codes were largely common to both)
Any advice on errors in/improvements to this spreadsheet are welcome!
Part 1:   Schematic layout of main electrical components/connectionsEngine connections
Main relay pack (2 plugs, large & small)Black PlugBlue PlugIndividual connections
ECU plugs (VVC:2×36 pin plugs; non-VVC: 1×36 pin plug)(Connections to the rest of the car)
Part 2:  What the wires do
Wire no(as arbitrarily identified by me in drawing this list up)
1.   Wires from the ECU plugs:
(a) Wires going between the ECU and the engine sensors (refer also 1 (e) below)
wireconnects toNotes
1Yellow/purpleMap sensor
2Red green   ”       “
3green browninlet air temp sensor
4green/orangeoil temperature sensor
5pink/greencoolant temperature sensor
6yellow/greenthrottle sensor
7yellow/purple     ”         “
8red/yellowcamshaft position sensor
9black/blue      ”            ”         “
10blue/purplecrankshaft postion sensor
11white/blue      ”            ”         “
12slateOxygen sensor
13light green/slate      ”         “
(b) Wires going from the ECU to engine functions
wireconnects to
14orange/slatestepper motor (idle air control valve)
15pink/blue     ”         “
16orange blue     ”         “
17orange green     ”         “
18yellow/brownNo 1 injector
19yellow/redNo 2 injector
20yellow/whiteNo 3 injector
21yellow/blackNo 4 injector
22white/blackignition coil 1
23white/blackignition coil 1
24black/brownVVC solenoid – increase
25black/yellowVVC solenoid – decrease
(c) Wires going from the ECU to the main relay pack
wireconnects tofunction
26black/greensmall plugoxygen sensor
27white/pinksmall plugsecurity link?   Activates ECU power-on relay
28black purplesmall plugsecurity link?   Activates fuel pump relay
(d) Power input wires
wirefunction
29brown/pink (1)12 volt input to all functions, switched on by ECU power-on relay in the main relay pack.
The power-on relay feeds via brown/pink to an internal junction in the loom, thence feeds 12V to
29aECU
29bpurge valve, with wire 40 – not required, (can be blanked off or the plug can simply be left free on its short piece of wire)
29cstepper motor (idle air control valve)
29dspeedo transducer (where fitted) – this can be blanked off
29eVVC solenoid valve – increase
29fVVC solenoid valve – decrease
29gcoil pack. If running an original early MGB/Midget electric tacho (loop type), locate and disconnect this wire at the junction
(make sure you have the coil pack feed, not something else!!)
The disconnected wire is then connected to the Midget’s original coil feed wire, and hey presto! the tacho works!
(See note at the end for how we did it)
Don’t cut this wire if you have the later voltage sensing tacho, (identified by a single white/black signal feed
 wire on the back of the tacho – in addition to the green power feed – rather than a white wire which goes through a loop).
29hBrown/pink (2)Injectorsthis one comes direct from the relay pack, not via the above junction.  (Same wire as 54 below, I counted it twice)
(refer (2) below)
(e) common between ECU and sensors:
wirefunction
30pink/black.This wire connects to an in-loom junction, thence to:
30aMap sensor
30binlet air temp sensor
30coil temperature sensor
30dcoolant temperature sensor
30ethrottle sensor
30falso joins to the engine bay temperature sensor
(This sensor is on the MGF bodywork, not the engine, so this wire doesn’t go to the engine, but to one of the other plugs – refer (3) below)
(f) Wires from the ECU to functions external of the engine (in the engine bay or elsewhere)
wireconnects viafunctionRetain or blank off?Comments
31yellow/redblue plugAlarm ECUretaincarries the coded security link between the two ECU’s
32black (4 wires)direct connectionEarth connectionsretainMost ECU functions, and some (but not all) of the sensors work by completing a circuit to earth
33pinkblack plugdiagnostic socketretainA useful socket to get and retain with the system
34blue/slateblack plugcooling fan (1)   102 dec CretainOnly one fan required, but keep both wires for actuate a fan relay in case I mixed them up!
35blue/yellowblack plug??cooling fan (2)  108 deg Cretain – just in case!(Note: As the ECU earths these wires, join them to the earth terminal of the relay primary.)
36slate/whiteblack plugengine bay temperatureblank off(As in 1(e), #30f above.  This sensor is on the MGF bodywork, not the engine, so
30fpink/blackblack plug     ”      ”           “blank offthese wires don’t go to the engine, but to one of the other plugs – refer (3) below)
37blue/redblack plugair conditioningblank off
38blue/greenblack plugair conditioningblank off
39blue/blackblack plugair conditioningblank off
40yellow/orangeown plugpurge valveblank offcan be blanked off or the plug can simply be left free on its short piece of wire
41slate/blueblue plugair conditioningblank off
42green/redblue pluginstrument packblank off
43brown/blackblue plugMGF engine bay cooling fanblank off
44white/blackblue pluginstrument pack, MGF tachoblank off,   OR ….Connect to the later B/Midget Smiths voltage sensing tacho
(This later tacho is identified by a single whit/black signal feed,
rather than a white wire running through a loop.
If you have this later tacho, don’t cut the brown pink feed wire to the coil!
2. Wires from the Main Relay Pack:
(a)  Wires connected to the relay pack via the small plug on the back of it
wiregoes to/comes fromviafunctionretain or blank off?Comments
45WhiteIgnition sw via fuse boxblue plugswitched 12V to actuate fuel pump relayretainjoin to fuse box where other white wires connect
46white/redign sw (starter position)blue plugstarter relay actuationretainjoin to white/red in Midget loom
47black/whiteAlarm ECUblue plugImobiliser link to starter relayretain
28black/purpleECUengine loomCompletes fuel pump activationretain
27white/pinkECUengine loomActivates ECU power-on relayretain
26black/greenECUengine loomoxygen sensor actuationretain
(b)  Wires connected to the relay pack via the large plug on the back of it
48brown, thick (1)Fuse box, 30A fuseown plug12V to ECU power-on relayretainThese two are separate wires coming from separate fuses.
49brown, thick (2)Fuse box, 30A fusesame plug12V via relay to:oxygen sensor heaterretainI used an additional fuse box to service them
starter solenoidretain(Part no 606253A, the common early BMC fuse box)
50brown/slateInertia Switchblue plug12V supply to:fuel pump, via relayretainThe other side of inertia switch is fed from
same fuse as brown (1) above, via a brown wire
The inertia switch is mounted on the body, not the engine.
51brown/redstarter solenoidengine loomretain
52white/purplefuel pumpblack plugmain feed to fuel pumpretainjoin to white fuel pump wire in Midget rear loom.
53blue/red (thick)oxygen sensor heaterengine loomretain
29brown/pink (1)junction inside engine loom12V supply as listed in 1(d) aboveretain
54brown/pink (2)injectorsengine loom12V supply for injectorsretain(Same wire as 29h above, I counted it twice)
3. Other engine functions connecting to the engine bay:
wiregoes to/comes fromviafunctionretain or blank off?Comments
55brown/yellowAlternatorblue plugexciter wireretainconnect to brown/yellow in Midget loom
56brown (very heavy)Altenatordirectmain feedretainconnect to main power terminal (battery, battery feed)
57red (thick-ish)Air conditioningblack pluga/c clutchblank offOR use for power feed to coil pack for loop-type tacho fitted (see note below)
58green/blueunknownblue plugCouldn’t work this one out.blank off!The car works fine without it!   (Temp gauge possibly)
59green/yellowreverse light switchblue plugreverse lightsretainconnect to green wire end of fuse in main fuse box
60green/brownreverse light switchblue plugreverse lightsretainconnect to green/brown in rear loom
61white/brownoil pressure switchblack plugoil pressure warning lightretainretained for possible use (we connected the original pressure gauge)
62brown/blueoil temperature sensorblack plugoil temp gaugeretainretained for possible use (we connected the original pressure gauge)
Part 3:   What to connect
1.  Summary
Connect these
wiregoes to/comes fromviafunctionConnect to
black/whiteAlarm ECU(Imobiliser link to starter relay)Alarm ECU
blue/slateECU to cooling fan (1), 102 dec C(fan-on signal)Earth side of actuating coil of new fan relay
brown/slateInertia Switch(cuts fuel pressure in event of accident)Inertia Switch. The other side of inertia switch is fed from the fuse box
brown/yellowAlternator(exciter wire)brown/yellow in Midget loom, goes to warning light
WhiteIgnition sense wire(ign switched 12V to actuate main relay)fuse box where other white wires connect
white/purplefuel pump(main feed to fuel pump)join to white fuel pump wire in Midget rear loom.
white/redign sw (starter position)(starter relay actuation)white/red in Midget loom
yellow/redECU to Alarm ECU(coded signal to & from alarm unit)Alarm ECU
plus:
brown (very heavy)Altenator(main charging circuit conenction)connect to main powr terminal (battery, battery feed)
black (4 wires)ECU to Earth connectionsearth (make sure it is a good one!)
brown, thick (1)Fuse box, 30A fuseon own plug12V supply to the ECU & harnessNew fuse box
brown, thick (2)Fuse box, 30A fusesame plug12V supply to oxygen sensor heaterNew fuse box
(these two 12 V supplies both go via the main relay pack where they are switched on and off by the white ignition sense wire)
Optional connections
blue/yellowECU to cooling fan (2)  108 deg Crun to fan relay as a stand-by, but don’t connect
brown/blueoil temperature sensor(oil temp gauge)carry through to dash for actual or potential oil temp gauge
green/brownreverse light switch(reverse lights)green/brown in Midget rear loom
green/yellowreverse light switch(reverse lights)green wire end of fuse in main fuse box
pinkECU to diagnostic socketRover diagnostic socket
white/blackTacho connectionConnect directly for RVC voltage-sensing type tacho, for loop type see note at the bottom of this spreadsheet
white/brownoil pressure switch(oil pressure warning light)carry through to behind dash for actual or potential oil pressure light
(Note re reverse lights: connecting as above eliminates the need for separate connections for the reverse lights, but retaining these as original won’t affect anything)
Don’t need
blue/black
blue/green
blue/red
brown/black
green/red
pink/black
red (thick-ish)but may be needed for loop-type tacho – see note at the bottom of this spreadsheet
slate/blue
slate/white
green/blue
yellow/orange(purge valve, on a separate plug)
2.  Plug-by-plug version of the above
(Note:  The wire no’s below are the same as those in part 2 above to aid in cross-referencing if you want to)
(a)  Black Plug
wiregoes to/comes fromviafunctionretain or blank off?Connect to
List sorted by wire clolour
39blue/blackECU to air conditioningblank off
38blue/greenECU to air conditioningblank off
37blue/redECU to air conditioningblank off
34blue/slateECU to cooling fan (1)   102 dec CretainEarth side of actuating coil of new fan relay
62brown/blueoil temperature sensoroil temp gaugeretaincarry through to dash for actual or potential oil temp gauge
33pinkECU to diagnostic socketretainRover diagnostic socket
30fpink/blackECU to      ”      ”           “blank off
57red (thick-ish)Air conditioninga/c clutchblank offOR use for power feed to coil pack for loop-type tacho fitted (see note below)
36slate/whiteECU to engine bay temperatureblank off
61white/brownoil pressure switchoil pressure warning lightretaincarry through to behind dash for actual or potential oil pressure light
52white/purplefuel pumpmain feed to fuel pumpretainjoin to white fuel pump wire in Midget rear loom.
35blue/yellowECU to cooling fan (2)  108 deg Cblack plug??retain – just in case!run to fan relay as a stand-by, but don’t connect
(b)  Blue Plug
List sorted by wire clolour
47black/whiteAlarm ECUImobiliser link to starter relayretainAlarm ECU
43brown/blackECU to MGF engine bay cooling fanblank off
50brown/slateInertia Switch12V supply to:fuel pump, via relayretainInertia Switch. The other side of inertia switch is fed from
same fuse as brown (1) above, via a brown wire
55brown/yellowAlternatorexciter wireretainbrown/yellow in Midget loom, goes to warning light
58green/blueunknownblank off!
60green/brownreverse light switchreverse lightsretaingreen/brown in Midget rear loom
42green/redECU to instrument packblank off
59green/yellowreverse light switchreverse lightsretaingreen wire end of fuse in main fuse box
41slate/blueECU to air conditioningblank off
45WhiteIgnition sw via fuse boxswitched 12V to actuate fuel pump relayretainfuse box where other white wires connect
44white/blackECU to instrument packblank off,   OR ….use this one as the link between tacho and the coil pack feed.
(Refer detail above.)
46white/redign sw (starter position)starter relay actuationretainwhite/red in Midget loom
31yellow/redECU to Alarm ECUretainAlarm ECU
(c)  Direct connection
56brown (very heavy)Altenatormain feedretainconnect to main powr terminal (battery, battery feed)
32black (4 wires)ECU to Earth connectionsretainearth (make sure it is a good one!)
(d)  Other plugs
48brown, thick (1)Fuse box, 30A fuseown plug12V to ECU power-on relayretainNew fuse box, as above
49brown, thick (2)Fuse box, 30A fusesame plug12V via relay to:oxygen sensor heaterretainNew fuse box, as above
40yellow/orangeECU to purge valveown plugblank offcan be blanked off or the plug can simply be left free on its short piece of wire
NOTEConnection for loop-type tacho
This tacho senses the current fluctuations in the primary circuit of the coil.
The original circuit goes:
Ignition switch – (white wire) => tacho loop – (still a white wire) => engine bay => coil +ve
We connected this original coil feed wire to the black plug, wire 57 – which was originally the red air conditioning clutch wire.
This red wire follows the same path within the engine loom as the coil pack brown/pink wire, making it easy to divert to this new function, and is also of a suitable size.
Inside the engine loom, we connected this red wire to the coil pack’s brown/pink wire, which was separated from the junction in 29(g) above
(It’s not the right colour, but it’s simply available in the plug and is the right size)
Although we made this connection in the middle of the loom by the multi-brown-pink junction, we worked out in the end that we could more simple have made this by
joining much closer to the coil pack, or even by diverting the red directly to the coil pack and fiting a new mini-spade to it.
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Paul Walbran Motors