In the last part of the 1.9TDi wiring write-up I covered stripping the unnecessary wiring from the main harness and identifying the connectors etc. which need to be retained for the cabin end of the harness/loom. This time I'm going to list the stuff you should be left with at the other end of the harness i.e. under the bonnet. The pic below shows what you should be left with having removed all of the redundant wiring. As mentioned previously, I have covered all of the connectors in section A below in part 1. The remainder are
B (EGR/MAF/N75)
C (ECU)
D (Engine/Crank sensor/oil pressure/Injector pump/etc.)
So what connectors should I be left with on the engine side of the firewall?
Well as I have a Golf 3 (1997) harness, this is what I found (other vehicles will be similar if not identical). The ECU connector(s) styles may differ if you have a later donor vehicle. The one I have is a Bosch 68 pin ECU so has a single connector later ones have 2 separate connectors. Below is an illustration of the connectors (numbered 1-9) from 'C' & 'D' above at the far end of the harness you should be left with:
1) Engine Multiplug
Numerous items connected here incl. glowplugs, temperature sensors, oil pressure sensors, etc. I won't cover all of the individually connected items as this connector is large and it's purpose is fairly obvious.
2) Inlet Temperature Sensor
Black two pin connector
Pin1 = brown/blue -> analogue ground -> pin33 ECU
Pin2 = blue/yelow -> pin64 ECU
This signal is used by the ECU to determine the temperature of the aircharge entering the engine from the intercooler and is used to adjust fuelling and control other engine parameters.
3) Injector Pump Connector
Black eight pin connector (only pins 1-7 are used)
Pin1 = purple/black -> modulating piston movement sensor -> pin29 ECU
Pin2 = grey/green -> modulating piston movement sensor -> pin7 ECU
Pin3 = white/green -> modulating piston movement sensor -> pin52 ECU
Pin4 = brown/blue -> analogue ground -> pin33 ECU
Pin5 = black/yellow -> pin 23 ECU (ECU sensor supply)
Pin6 = brown/yellow -> metering adjuster -> pin49 ECU
Pin7 = yellow/black -> fuel temperature sensor -> pin63 ECU
This connector handles the fuelling and injection timing adjustments as well as the fuel temp. measurement.
4) Alternator Field Coils
Note that this should be connected to a 2 pin connector that fits the alternator, as I didn't remove the loom from my donor vehicle the person who did cut the connector off in error. Suffice to say that this should be connected to D+ on the alternator itself. The wire is plain blue and is connected to pin 3 of fusebox connector 'F' as shown below.
5) Starter Solenoid
Black single pin connector
Pin1 = red/black -> starter solenoid -> pin1 connector 'F' fusebox
This is the main switched supply to the starter solenoid and is carried from the ignition switch through the fusebox to pin1 of connector 'F'
6) Reverse Light Switch
Black two pin connector
Pin1 = black/blue -> (switched side) reversing lights -> pin7 connector 'F'
Pin2 = black/red -> +12V supply - terminal 15 via fuse S14 (10A) -> pin6 connector 'F'
Self explanatory I think.
7) ECU 68 Pin Connector
Black 68 pin locking connector
Not going to list all 68 of these but will include them later as a list for people to use if required
8) Crank Position/speed Sensor
Black three pin connector
Pin1 = black -> analogue ground -> pin33 ECU
Pin2 = blue -> crank speed sensor i/p -> pin8 ECU
Pin3 = grey -> battery ground -> pin1 ECU
This signal is used by the ECU to determine the crank speed and position. This has a direct bearing on injection timing/quantity and a number of other parameters.
9) Needle Lift Sensor
Brown two pin connector
Pin1 = grey -> pin12 ECU
pin2 = blue -> pin11 ECU
This sensor is used to calculate the actual point of commencement of fuel injection from the time difference between the signal of the needle lift and the TDC signal supplied by the crank speed/position sensor. At the same time, the ECU compares the actual point of commencement of injection with the setpoint stored in the control map and corrects any deviations from that setpoint.
At the other end of the harness and adjacent to the fusebox connectors are three other connectors shown below:
1) Boost Control Valve (N75)
Black two pin connector
Pin1 = black/yellow -> sensor supply +12V (terminal 15) -> pin23 ECU
Pin2 = red/blue -> pin47 ECU
This signal is used by the ECU to regulate boost depending on engine speed, throttle position, and other engine parameters.
2) Mass Airflow Sensor MAF
Black six pin connector (pin 4 unused)
Pin1 = red/green -> pin19 ECU
Pin2 = brown/blue -> analogue ground pin33 ECU
Pin3 = black/yellow -> sensor supply +12V (terminal 15) d -> pin24 ECU
Pin4 = N/C
Pin5 = brown -> pin23 ECU
Pin6 = brown/red -> pin13 ECU
This signal is used to measure the airflow entering the inlet. Fuel and injection timing etc. are then adjusted accordingly
2)EGR Control Solenoid (N18)
Black two pin connector
Pin1 = black/yellow -> sensor supply +12V (terminal 15) -> pin23 ECU
Pin2 = brown/white -> pin25 ECU
This signal is used by the ECU to regulate the EGR phase when the motor is at low/idle engine speeds. It is driven by a PWM signal whose duty cycle is varied depending on a number of atmospheric (baro pressure etc.)/engine conditions.
So do I need to make any other modifications to my wiring harness?
In the old engine harness you removed from the van, there is a pair of wires which are connected to the instrument cluster via a two pin inline connector on one end and the header coolant level sensor at the other. They look like this:
and these are the connectors (top = fusebox end, bottom = coolant header tank end):
.
You need to slice the tape open on the old engine harness and remove this part. Once you have done this, remove the bit shown above, attach it to the new TDI harness and re-connect at both ends.
A useful tip also is not to tape the stripped out TDI harness-up until you have figured out how it is routed around the T4 engine bay, when you are happy then get to work with the tape. This will allow you to take all the curves/bends in the harness in account and make the routing neater when applying your choice of tape - I used self-amalgamating tape but ordinary insulation tape is fine also.
And that's it. I welcome any information which I can use to add further detail to this guide in the form of circuit diagrams for other vehicles/ECUs so that it will in time develop into a more comprehensive source of info. Happy tdi'ing
Additional ECU pin out info:
1.9TDI 68-Pin ECU Pinout (p/ns: 028 906 02X xx)
Copied from a 1997 Golf TDI diagram – note: all pins are included below, but not necessarily used
No code has to be inserted here.
No code has to be inserted here.
B (EGR/MAF/N75)
C (ECU)
D (Engine/Crank sensor/oil pressure/Injector pump/etc.)

So what connectors should I be left with on the engine side of the firewall?
Well as I have a Golf 3 (1997) harness, this is what I found (other vehicles will be similar if not identical). The ECU connector(s) styles may differ if you have a later donor vehicle. The one I have is a Bosch 68 pin ECU so has a single connector later ones have 2 separate connectors. Below is an illustration of the connectors (numbered 1-9) from 'C' & 'D' above at the far end of the harness you should be left with:

1) Engine Multiplug
Numerous items connected here incl. glowplugs, temperature sensors, oil pressure sensors, etc. I won't cover all of the individually connected items as this connector is large and it's purpose is fairly obvious.
2) Inlet Temperature Sensor
Black two pin connector
Pin1 = brown/blue -> analogue ground -> pin33 ECU
Pin2 = blue/yelow -> pin64 ECU
This signal is used by the ECU to determine the temperature of the aircharge entering the engine from the intercooler and is used to adjust fuelling and control other engine parameters.
3) Injector Pump Connector
Black eight pin connector (only pins 1-7 are used)
Pin1 = purple/black -> modulating piston movement sensor -> pin29 ECU
Pin2 = grey/green -> modulating piston movement sensor -> pin7 ECU
Pin3 = white/green -> modulating piston movement sensor -> pin52 ECU
Pin4 = brown/blue -> analogue ground -> pin33 ECU
Pin5 = black/yellow -> pin 23 ECU (ECU sensor supply)
Pin6 = brown/yellow -> metering adjuster -> pin49 ECU
Pin7 = yellow/black -> fuel temperature sensor -> pin63 ECU
This connector handles the fuelling and injection timing adjustments as well as the fuel temp. measurement.
4) Alternator Field Coils
Note that this should be connected to a 2 pin connector that fits the alternator, as I didn't remove the loom from my donor vehicle the person who did cut the connector off in error. Suffice to say that this should be connected to D+ on the alternator itself. The wire is plain blue and is connected to pin 3 of fusebox connector 'F' as shown below.

5) Starter Solenoid
Black single pin connector
Pin1 = red/black -> starter solenoid -> pin1 connector 'F' fusebox
This is the main switched supply to the starter solenoid and is carried from the ignition switch through the fusebox to pin1 of connector 'F'
6) Reverse Light Switch
Black two pin connector
Pin1 = black/blue -> (switched side) reversing lights -> pin7 connector 'F'
Pin2 = black/red -> +12V supply - terminal 15 via fuse S14 (10A) -> pin6 connector 'F'
Self explanatory I think.
7) ECU 68 Pin Connector
Black 68 pin locking connector
Not going to list all 68 of these but will include them later as a list for people to use if required
8) Crank Position/speed Sensor
Black three pin connector
Pin1 = black -> analogue ground -> pin33 ECU
Pin2 = blue -> crank speed sensor i/p -> pin8 ECU
Pin3 = grey -> battery ground -> pin1 ECU
This signal is used by the ECU to determine the crank speed and position. This has a direct bearing on injection timing/quantity and a number of other parameters.
9) Needle Lift Sensor
Brown two pin connector
Pin1 = grey -> pin12 ECU
pin2 = blue -> pin11 ECU
This sensor is used to calculate the actual point of commencement of fuel injection from the time difference between the signal of the needle lift and the TDC signal supplied by the crank speed/position sensor. At the same time, the ECU compares the actual point of commencement of injection with the setpoint stored in the control map and corrects any deviations from that setpoint.
At the other end of the harness and adjacent to the fusebox connectors are three other connectors shown below:

1) Boost Control Valve (N75)
Black two pin connector
Pin1 = black/yellow -> sensor supply +12V (terminal 15) -> pin23 ECU
Pin2 = red/blue -> pin47 ECU
This signal is used by the ECU to regulate boost depending on engine speed, throttle position, and other engine parameters.
2) Mass Airflow Sensor MAF
Black six pin connector (pin 4 unused)
Pin1 = red/green -> pin19 ECU
Pin2 = brown/blue -> analogue ground pin33 ECU
Pin3 = black/yellow -> sensor supply +12V (terminal 15) d -> pin24 ECU
Pin4 = N/C
Pin5 = brown -> pin23 ECU
Pin6 = brown/red -> pin13 ECU
This signal is used to measure the airflow entering the inlet. Fuel and injection timing etc. are then adjusted accordingly
2)EGR Control Solenoid (N18)
Black two pin connector
Pin1 = black/yellow -> sensor supply +12V (terminal 15) -> pin23 ECU
Pin2 = brown/white -> pin25 ECU
This signal is used by the ECU to regulate the EGR phase when the motor is at low/idle engine speeds. It is driven by a PWM signal whose duty cycle is varied depending on a number of atmospheric (baro pressure etc.)/engine conditions.
So do I need to make any other modifications to my wiring harness?
In the old engine harness you removed from the van, there is a pair of wires which are connected to the instrument cluster via a two pin inline connector on one end and the header coolant level sensor at the other. They look like this:

and these are the connectors (top = fusebox end, bottom = coolant header tank end):

You need to slice the tape open on the old engine harness and remove this part. Once you have done this, remove the bit shown above, attach it to the new TDI harness and re-connect at both ends.
A useful tip also is not to tape the stripped out TDI harness-up until you have figured out how it is routed around the T4 engine bay, when you are happy then get to work with the tape. This will allow you to take all the curves/bends in the harness in account and make the routing neater when applying your choice of tape - I used self-amalgamating tape but ordinary insulation tape is fine also.
And that's it. I welcome any information which I can use to add further detail to this guide in the form of circuit diagrams for other vehicles/ECUs so that it will in time develop into a more comprehensive source of info. Happy tdi'ing
Additional ECU pin out info:
1.9TDI 68-Pin ECU Pinout (p/ns: 028 906 02X xx)
Copied from a 1997 Golf TDI diagram – note: all pins are included below, but not necessarily used
No code has to be inserted here.
No code has to be inserted here.