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/connections Engine connections
Main relay pack (2 plugs, large & small) Black Plug Blue Plug Individual 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)
wire connects to Notes
1 Yellow/purple Map sensor
2 Red green    ”       “
3 green brown inlet air temp sensor
4 green/orange oil temperature sensor
5 pink/green coolant temperature sensor
6 yellow/green throttle sensor
7 yellow/purple      ”         “
8 red/yellow camshaft position sensor
9 black/blue       ”            ”         “
10 blue/purple crankshaft postion sensor
11 white/blue       ”            ”         “
12 slate Oxygen sensor
13 light green/slate       ”         “
(b) Wires going from the ECU to engine functions
wire connects to
14 orange/slate stepper motor (idle air control valve)
15 pink/blue      ”         “
16 orange blue      ”         “
17 orange green      ”         “
18 yellow/brown No 1 injector
19 yellow/red No 2 injector
20 yellow/white No 3 injector
21 yellow/black No 4 injector
22 white/black ignition coil 1
23 white/black ignition coil 1
24 black/brown VVC solenoid – increase
25 black/yellow VVC solenoid – decrease
(c) Wires going from the ECU to the main relay pack
wire connects to function
26 black/green small plug oxygen sensor
27 white/pink small plug security link?   Activates ECU power-on relay
28 black purple small plug security link?   Activates fuel pump relay
(d) Power input wires
wire function
29 brown/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
29a ECU
29b purge valve, with wire 40 – not required, (can be blanked off or the plug can simply be left free on its short piece of wire)
29c stepper motor (idle air control valve)
29d speedo transducer (where fitted) – this can be blanked off
29e VVC solenoid valve – increase
29f VVC solenoid valve – decrease
29g coil 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).
29h Brown/pink (2) Injectors this 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:
wire function
30 pink/black. This wire connects to an in-loom junction, thence to:
30a Map sensor
30b inlet air temp sensor
30c oil temperature sensor
30d coolant temperature sensor
30e throttle sensor
30f also 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)
wire connects via function Retain or blank off? Comments
31 yellow/red blue plug Alarm ECU retain carries the coded security link between the two ECU’s
32 black (4 wires) direct connection Earth connections retain Most ECU functions, and some (but not all) of the sensors work by completing a circuit to earth
33 pink black plug diagnostic socket retain A useful socket to get and retain with the system
34 blue/slate black plug cooling fan (1)   102 dec C retain Only one fan required, but keep both wires for actuate a fan relay in case I mixed them up!
35 blue/yellow black plug?? cooling fan (2)  108 deg C retain – just in case! (Note: As the ECU earths these wires, join them to the earth terminal of the relay primary.)
36 slate/white black plug engine bay temperature blank off (As in 1(e), #30f above.  This sensor is on the MGF bodywork, not the engine, so
30f pink/black black plug      ”      ”           “ blank off these wires don’t go to the engine, but to one of the other plugs – refer (3) below)
37 blue/red black plug air conditioning blank off
38 blue/green black plug air conditioning blank off
39 blue/black black plug air conditioning blank off
40 yellow/orange own plug purge valve blank off can be blanked off or the plug can simply be left free on its short piece of wire
41 slate/blue blue plug air conditioning blank off
42 green/red blue plug instrument pack blank off
43 brown/black blue plug MGF engine bay cooling fan blank off
44 white/black blue plug instrument pack, MGF tacho blank 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
wire goes to/comes from via function retain or blank off? Comments
45 White Ignition sw via fuse box blue plug switched 12V to actuate fuel pump relay retain join to fuse box where other white wires connect
46 white/red ign sw (starter position) blue plug starter relay actuation retain join to white/red in Midget loom
47 black/white Alarm ECU blue plug Imobiliser link to starter relay retain
28 black/purple ECU engine loom Completes fuel pump activation retain
27 white/pink ECU engine loom Activates ECU power-on relay retain
26 black/green ECU engine loom oxygen sensor actuation retain
(b)  Wires connected to the relay pack via the large plug on the back of it
48 brown, thick (1) Fuse box, 30A fuse own plug 12V to ECU power-on relay retain These two are separate wires coming from separate fuses.
49 brown, thick (2) Fuse box, 30A fuse same plug 12V via relay to: oxygen sensor heater retain I used an additional fuse box to service them
starter solenoid retain (Part no 606253A, the common early BMC fuse box)
50 brown/slate Inertia Switch blue plug 12V supply to: fuel pump, via relay retain The 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.
51 brown/red starter solenoid engine loom retain
52 white/purple fuel pump black plug main feed to fuel pump retain join to white fuel pump wire in Midget rear loom.
53 blue/red (thick) oxygen sensor heater engine loom retain
29 brown/pink (1) junction inside engine loom 12V supply as listed in 1(d) above retain
54 brown/pink (2) injectors engine loom 12V supply for injectors retain (Same wire as 29h above, I counted it twice)
3. Other engine functions connecting to the engine bay:
wire goes to/comes from via function retain or blank off? Comments
55 brown/yellow Alternator blue plug exciter wire retain connect to brown/yellow in Midget loom
56 brown (very heavy) Altenator direct main feed retain connect to main power terminal (battery, battery feed)
57 red (thick-ish) Air conditioning black plug a/c clutch blank off OR use for power feed to coil pack for loop-type tacho fitted (see note below)
58 green/blue unknown blue plug Couldn’t work this one out. blank off! The car works fine without it!   (Temp gauge possibly)
59 green/yellow reverse light switch blue plug reverse lights retain connect to green wire end of fuse in main fuse box
60 green/brown reverse light switch blue plug reverse lights retain connect to green/brown in rear loom
61 white/brown oil pressure switch black plug oil pressure warning light retain retained for possible use (we connected the original pressure gauge)
62 brown/blue oil temperature sensor black plug oil temp gauge retain retained for possible use (we connected the original pressure gauge)
Part 3:   What to connect
1.  Summary
Connect these
wire goes to/comes from via function Connect to
black/white Alarm ECU (Imobiliser link to starter relay) Alarm ECU
blue/slate ECU to cooling fan (1), 102 dec C (fan-on signal) Earth side of actuating coil of new fan relay
brown/slate Inertia Switch (cuts fuel pressure in event of accident) Inertia Switch. The other side of inertia switch is fed from the fuse box
brown/yellow Alternator (exciter wire) brown/yellow in Midget loom, goes to warning light
White Ignition sense wire (ign switched 12V to actuate main relay) fuse box where other white wires connect
white/purple fuel pump (main feed to fuel pump) join to white fuel pump wire in Midget rear loom.
white/red ign sw (starter position) (starter relay actuation) white/red in Midget loom
yellow/red ECU 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 connections earth (make sure it is a good one!)
brown, thick (1) Fuse box, 30A fuse on own plug 12V supply to the ECU & harness New fuse box
brown, thick (2) Fuse box, 30A fuse same plug 12V supply to oxygen sensor heater New 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/yellow ECU to cooling fan (2)  108 deg C run to fan relay as a stand-by, but don’t connect
brown/blue oil temperature sensor (oil temp gauge) carry through to dash for actual or potential oil temp gauge
green/brown reverse light switch (reverse lights) green/brown in Midget rear loom
green/yellow reverse light switch (reverse lights) green wire end of fuse in main fuse box
pink ECU to diagnostic socket Rover diagnostic socket
white/black Tacho connection Connect directly for RVC voltage-sensing type tacho, for loop type see note at the bottom of this spreadsheet
white/brown oil 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
wire goes to/comes from via function retain or blank off? Connect to
List sorted by wire clolour
39 blue/black ECU to air conditioning blank off
38 blue/green ECU to air conditioning blank off
37 blue/red ECU to air conditioning blank off
34 blue/slate ECU to cooling fan (1)   102 dec C retain Earth side of actuating coil of new fan relay
62 brown/blue oil temperature sensor oil temp gauge retain carry through to dash for actual or potential oil temp gauge
33 pink ECU to diagnostic socket retain Rover diagnostic socket
30f pink/black ECU to      ”      ”           “ blank off
57 red (thick-ish) Air conditioning a/c clutch blank off OR use for power feed to coil pack for loop-type tacho fitted (see note below)
36 slate/white ECU to engine bay temperature blank off
61 white/brown oil pressure switch oil pressure warning light retain carry through to behind dash for actual or potential oil pressure light
52 white/purple fuel pump main feed to fuel pump retain join to white fuel pump wire in Midget rear loom.
35 blue/yellow ECU to cooling fan (2)  108 deg C black 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
47 black/white Alarm ECU Imobiliser link to starter relay retain Alarm ECU
43 brown/black ECU to MGF engine bay cooling fan blank off
50 brown/slate Inertia Switch 12V supply to: fuel pump, via relay retain Inertia Switch. The other side of inertia switch is fed from
same fuse as brown (1) above, via a brown wire
55 brown/yellow Alternator exciter wire retain brown/yellow in Midget loom, goes to warning light
58 green/blue unknown blank off!
60 green/brown reverse light switch reverse lights retain green/brown in Midget rear loom
42 green/red ECU to instrument pack blank off
59 green/yellow reverse light switch reverse lights retain green wire end of fuse in main fuse box
41 slate/blue ECU to air conditioning blank off
45 White Ignition sw via fuse box switched 12V to actuate fuel pump relay retain fuse box where other white wires connect
44 white/black ECU to instrument pack blank off,   OR …. use this one as the link between tacho and the coil pack feed.
(Refer detail above.)
46 white/red ign sw (starter position) starter relay actuation retain white/red in Midget loom
31 yellow/red ECU to Alarm ECU retain Alarm ECU
(c)  Direct connection
56 brown (very heavy) Altenator main feed retain connect to main powr terminal (battery, battery feed)
32 black (4 wires) ECU to Earth connections retain earth (make sure it is a good one!)
(d)  Other plugs
48 brown, thick (1) Fuse box, 30A fuse own plug 12V to ECU power-on relay retain New fuse box, as above
49 brown, thick (2) Fuse box, 30A fuse same plug 12V via relay to: oxygen sensor heater retain New fuse box, as above
40 yellow/orange ECU to purge valve own plug blank off can be blanked off or the plug can simply be left free on its short piece of wire
NOTE Connection 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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