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> Convert back to D Jet Fuel Injection-, Wire harnessess- Injector Ground
young55961
post Jun 18 2026, 02:34 PM
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I have a question about the ECU wiring harness.

There are three pairs of white wires with female spade terminals on the harness. I believe they are the ground wires for the fuel injectors, but I can't find where they are supposed to connect.

Should these wires be connected to the negative (-) terminal of the ignition coil?

If anyone has a photo showing the correct connection, I would really appreciate it. Thank you!
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brant
post Jun 18 2026, 02:46 PM
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There was supposed to be a three prong connector on the rear engine block through bolt

Back center of engine bay
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JeffBowlsby
post Jun 18 2026, 02:46 PM
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2 of the three pairs are injector grounds. The third pair is grounds for the ECU and TPS.

They attach to a Tri-spade male terminal located on an engine case through-bolt at the top rear of the engine case, under the air plenum.
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young55961
post Jun 18 2026, 02:52 PM
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QUOTE(JeffBowlsby @ Jun 18 2026, 03:46 PM) *

2 of the three pairs are injector grounds. The third pair is grounds for the ECU and TPS.

They attach to a Tri-spade male terminal located on an engine case through-bolt at the top rear of the engine case, under the air plenum.


Tks.
Let me check.
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Ishley
post Jun 18 2026, 08:12 PM
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Here is what you’re looking for in the yellow circle.


Attached image(s)
Attached Image
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young55961
post Jun 19 2026, 10:54 AM
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QUOTE(Ishley @ Jun 18 2026, 09:12 PM) *

Here is what you’re looking for in the yellow circle.



Unfortunately I don't have one there. Most likely get delete during the conversion process.


Thank you anyway.
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Jack Standz
post Jun 19 2026, 03:44 PM
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It's easy enough to get one. Here's one example, but there are others available:

https://www.ebay.com/itm/168409193204
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DC_neun_vierzehn
post Jun 19 2026, 03:54 PM
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QUOTE(Ishley @ Jun 18 2026, 08:12 PM) *

Here is what you’re looking for in the yellow circle.


@Ishley What motor is this?

The location of the tri-spade ground is different on my ‘73 2.0 motor.

@young55961 what is the year and motor on your 914?
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Ishley
post Jun 19 2026, 04:25 PM
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Mine is a '72 1.7 that I rebuilt into a 2056. The ground spade is stock and in the stock location.

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young55961
post Jun 19 2026, 08:17 PM
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QUOTE(DC_neun_vierzehn @ Jun 19 2026, 04:54 PM) *

QUOTE(Ishley @ Jun 18 2026, 08:12 PM) *

Here is what you’re looking for in the yellow circle.


@Ishley What motor is this?

The location of the tri-spade ground is different on my ‘73 2.0 motor.

@young55961 what is the year and motor on your 914?

My 75 2.0L
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Dave_Darling
post Jun 19 2026, 09:27 PM
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Mine is further back, right by the flywheel end of the motor. But still up on top. Really, any case bolt should work for a ground.

--DD
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DC_neun_vierzehn
post Jun 22 2026, 05:27 AM
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QUOTE(Dave_Darling @ Jun 19 2026, 09:27 PM) *

Mine is further back, right by the flywheel end of the motor. But still up on top. Really, any case bolt should work for a ground.

--DD


Same.
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robkammer
post Jun 23 2026, 05:38 AM
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Mine is right at the top of the case split at the flywheel. The lower position makes it VERY difficult to get to as it’s under the plenum.
Rob
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friethmiller
post Jun 23 2026, 07:33 AM
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(IMG:style_emoticons/default/popcorn[1].gif)

Observing... learning. I'll be doing this to my LE soon. Jeff B has already tested my ECU but I will be dealing with wiring, the MPS, and other components in a few months probably.
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young55961
post Nov 1 2026, 12:22 PM
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I'm trying to test-run my 1975 Porsche 914 2.0L D-Jetronic engine outside the car, and I have a few questions about the relay board and wiring harness.

Attached Image

The two pins inside the red square both show 12V with the ignition ON. Is this correct? I also tested the other two pins, but neither appears to be connected to ground.

Attached Image

It seems that the wiring arrangement may be incorrect.

From my understanding:
- **#31** should be ground.
- **#24 and #19** should receive 12V.
- **#18** should receive 12V temporarily while cranking the engine.

Am I understanding these connections correctly? I want to make sure I supply power to the correct terminals before attempting to start the engine outside the car.

Also, I'm not sure whether I should start a new thread for these questions or continue posting in this thread.

Any advice would be greatly appreciated. Thanks!
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GregAmy
post Nov 1 2026, 12:31 PM
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From my Microsquirt build notes.

T4-I
.75 and .5mm
Into ECU pin 16 (.75) and 24 (.5)
Circuit 87, powered by engagement of the power relay. Medium-size circuit, relayed from large 30.
#24, .75mm (~18AWG) goes to injector drivers.
#16 .5mm (~20AWG) goes to power ECU and sensors.

T4-II
.5mm
Into ECU pin 18, power from T14-1 (track 81) start power to starter solenoid via 12-6; signal to ECU of start circuit

T4-III
.5mm
Into ECU pin 19 86, ground side for fuel pump relay.

T4-IV
.5mm
Power from T14-1 (track 81) start power to starter solenoid via 12-6; CSV engagement


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Dave_Darling
post Nov 1 2026, 07:04 PM
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I'm pretty sure that #31 should get grounded by the ECU when it sees that the engine is rotating. It does not get a full-time ground.

--DD
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JamesM
post Nov 2 2026, 12:58 AM
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QUOTE(Dave_Darling @ Nov 1 2026, 05:04 PM) *

I'm pretty sure that #31 should get grounded by the ECU when it sees that the engine is rotating. It does not get a full-time ground.

--DD


^That


There are no grounds on the 4 pin. everything with the injection grounds through the tri-spade on the case. #31 activates the pump relay. If you ever want to test your fuel pump/pump relay just jumper that pin to the chassis/ground.
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