944T New Harness Relay Box - Sanity Check

[944m3]

I’ve been really happy with my MaxxECU. Became comfortable enough to wire in extra sensors and EBC. And that’s using the custom adapter harness and using the stock harness. Now I think I’m ready to tackle building my own harness. I would love to afford to purchase a ready built harness but want to save the money for a new AC system for next summer and I’m also replacing all my power steering hoses. Like to have my power steering back.

That being said, I love the challenge and there is something to say for having actually build something yourself. Which I think is the spirit of this board and the 951.

I’ve purchased the MaxxECU relay and fuse box. I’ve done some reading and I think it’s starting to make sense to me. So sanity check, is the fuel pump wiring the only thing I need to replace/move from under the stock fuse box? Or do I need to move ignition wires (from ignition key). Another question, the wiring coming from the DME through the 14 pin connector only powers the sensors? Meaning nothing else in the fuse box is grabbing power from the DME?

I might decide I’m over my head and just use the stock relays. But if I’m getting this right, it should be doable. Or am I crazy.

[fasterfaster]

What is the MaxxECU box giving you that the stock fuse box doesn't? Do you need more circuits?

Seems like there are some big benefits to going to a solid state PDM like the MaxxECU PDM20 to replace your relays (and potentially add direct ECU/CAN control), but that is a different level of expense, and still can't replace the 50+ fused circuits on a street stock vehicle. And ff you're just using standard mechanical relays and fuses, then its no different than the stock box.

[944m3]

I wouldn’t replace all the fuses just what connects to the 14 pin connector. the fuel pump relay being the main one.

The idea is to replace old wiring and connections.

[Bergerac]

Im going to ask you a couple of questions that should help you becuase only you know what your furture plans are ATM (hopefully it doesnt come across as condecending)

- What do you need to power in the engine harness? (12V, 5V, load sizes and fusing requirements)
- What relays do you need and what relays currently exist in the car? (Below questions will help with this, using whats there will save you time and money)
- What does the ECU need to interface with in the car thats not in the engine harness? (Can you use the spare relay locations in the existing fuse relay panel for additions?)
- If youre adding additional components where can you mount them so they are easily accessible when you need to check fuses/change relays? (The Maxx fuse panel looks great but its going to be a PITA mounted under the dash)
- What Ignition system are you planning to use? Stock? Batch fire coil? Individual coil? (If youre drawing additional power is it worth relocating this supply from being powered directly from the IGN switch?)
- Are you planning to stick with the stock fuel system? (Upgraded pumps will need more power than the stock wiring can handle)
- Are you planning to use DBW?
- Please spend the money on a CAN O2 sensor if its not wired directly into your Maxx. (Not even a question, just do it)

Spend a few days with Sheet 7 of the wiring Diagram and the Maxx wiring instructions will help you not make an absoulete mess of the harness which will require hacking up later when you have issues and when things do go wrong. a good fundamental understanding of the harness and correct wiring techniques for your ECU will make problem solving so much easier (The number of people wiring the temp sensor back through MP VIII makes my blood boil).

Im happy to help with drawings, I have the whole set for the 90 model stictched together in PDF, be careful to get the drawings for your exactly year as there are small differences that will trip you up.

PDMs are great but it will multiply the complexity of your harness, the great thing about these cars is that a lot of the ancillary systems are self contained (ie Fans,A/C) and you can save time and money by letting them do thier own thing.

Really have a think about what additional functionality your Maxx has that you can use for engine protection or more acurate fueling, so many people go out and buy the top of the range ECU and then dont use any of the additional functionality. (Fuel Temp/Pressure, Oil Temp/Pressure are just a start)

[AudiSport]

I wouldn’t replace all the fuses just what connects to the 14 pin connector. the fuel pump relay being the main one.

The idea is to replace old wiring and connections.

I just ordered a plug and tapped the 14 pin connector. No reason not to use it, You're going to need it anyway for passthrough wires to keep temp/oil gauges working on the cluster, aux water pump if you want to keep that.. also tapped the AC pin to a DIN on maxx so the ECU knows when the AC is on and can idle up etc. Then I wired out a GPO to a relay so I can have the ECU shut off power to the AC say at heavy throttle...

The only relays I added were for the power hold function.

Here's what I laid out.

Pin 2 12V to Ignition 12 pin
Pin 3 12V to ECU/INJ 12 pin
Pin 4
Pin 5 GND trigger Fuel GPO5
Pin 6 Oil Pressure Gauge Term G
Pin 7
Pin 8 Cluster Temp
Pin 9 Oil Pres Term WK
Pin 10 Cluster Temp Small connector
Pin 11 Aux Water pump
Pin 12 GPO 6 GND Spare
Pin 13 AC IN
Pin 14 GPO 15 12V Spare

Replacing everything the engine harness did is really the only goal you probably need. But enhanced with more sensors.

[944m3]

Thanks for the response.

I completely agree with using the full capacity of the ECU. Which I am, such as boost limit with fuel cut off, RPM limit, oil pressure sensor wired to ECU and Wide Band Sensor with AFR and fuel trimming.

So in short, I’m comfortable with the ECU and wiring. This brings me to why I want to build a new harness. Which then made me think if I should also use new relay box. The purpose being to having all new wiring.

But sounds like perhaps I don’t need it. I haven’t lifted the stock box to see the condition of the wiring, but I can’t say I’m having any issues with the fuse box. I could always add it later if needed. To be clear, I’m not looking to add any new functionality that would require more power.

Any other thoughts/advice is welcomed.

[944m3]

I wouldn’t replace all the fuses just what connects to the 14 pin connector. the fuel pump relay being the main one.

The idea is to replace old wiring and connections.

I just ordered a plug and tapped the 14 pin connector. No reason not to use it, You're going to need it anyway for passthrough wires to keep temp/oil gauges working on the cluster, aux water pump if you want to keep that.. also tapped the AC pin to a DIN on maxx so the ECU knows when the AC is on and can idle up etc. Then I wired out a GPO to a relay so I can have the ECU shut off power to the AC say at heavy throttle...

The only relays I added were for the power hold function.

Here's what I laid out.

Pin 2 12V to Ignition 12 pin
Pin 3 12V to ECU/INJ 12 pin
Pin 4
Pin 5 GND trigger Fuel GPO5
Pin 6 Oil Pressure Gauge Term G
Pin 7
Pin 8 Cluster Temp
Pin 9 Oil Pres Term WK
Pin 10 Cluster Temp Small connector
Pin 11 Aux Water pump
Pin 12 GPO 6 GND Spare
Pin 13 AC IN
Pin 14 GPO 15 12V Spare

Replacing everything the engine harness did is really the only goal you probably need. But enhanced with more sensors.

Right, all I want to do is replace everything the current harness does, and integrate the new sensors I’ve added using auxiliary plugs. But in my mind that would include the relay box. As I said before, just to get it all new.

Now here is where things get fuzz for me. Couldn’t you run the oil/temp/aux pump from the new relay box? Then use the 8 pin flat connector in the foot well passenger side to get the signals to the cluster?

[AudiSport]

The only thing in the 8 pin connector is tach and oil level sensor.

[944m3]

“Then I wired out a GPO to a relay so I can have the ECU shut off power to the AC say at heavy throttle...”

Cool. Was this a separate relay outside of the stock fuse box?

[Bergerac]

I wouldn’t replace all the fuses just what connects to the 14 pin connector. the fuel pump relay being the main one.

The idea is to replace old wiring and connections.

I just ordered a plug and tapped the 14 pin connector. No reason not to use it, You're going to need it anyway for passthrough wires to keep temp/oil gauges working on the cluster, aux water pump if you want to keep that.. also tapped the AC pin to a DIN on maxx so the ECU knows when the AC is on and can idle up etc. Then I wired out a GPO to a relay so I can have the ECU shut off power to the AC say at heavy throttle...

The only relays I added were for the power hold function.

Here's what I laid out.

Pin 2 12V to Ignition 12 pin
Pin 3 12V to ECU/INJ 12 pin
Pin 4
Pin 5 GND trigger Fuel GPO5
Pin 6 Oil Pressure Gauge Term G
Pin 7
Pin 8 Cluster Temp
Pin 9 Oil Pres Term WK
Pin 10 Cluster Temp Small connector
Pin 11 Aux Water pump
Pin 12 GPO 6 GND Spare
Pin 13 AC IN
Pin 14 GPO 15 12V Spare

Replacing everything the engine harness did is really the only goal you probably need. But enhanced with more sensors.

Right, all I want to do is replace everything the current harness does, and integrate the new sensors I’ve added using auxiliary plugs. But in my mind that would include the relay box. As I said before, just to get it all new.

Now here is where things get fuzz for me. Couldn’t you run the oil/temp/aux pump from the new relay box? Then use the 8 pin flat connector in the foot well passenger side to get the signals to the cluster?

Like I said, you need to sit down and understand the drawing, what the relays do and how the engine harness interfaces with the dash and body harness. Audisport has given you the answer.