Custom Wiring Harness Cable Length

[christoph]

Hi Forum!


I am currently in the process of building my first wiring harness for a engine swap project.


Unfortunately i cannot physically mount the engine in the car yet - but i want to finish as much as possible before i rent a space to do the swap.


I plan to locate the ECU/PDM under the dashboard Firewall Passenger Seat. Can anyone recommend me a cable length from ECU to Cranksensor. The Cranksensor on my Swap-Engine is the first sensor closest to the firewall - right behind the transmission adapter - approximately 10cm away from the firewall. And approximately same height as the stock fa20 clutch cylinder - I would measure all the other cable lengths from there.


But how long should the cable be form ECU to Cransensor? - where did you drill a whole through the firewall?


I understand that this question is a rough estimate - pictures of your cable routing would be highly appreciated too...


Maybe sbd has some recommendations...


Best regards


Christoph

[blsfrs]

Are you doing a F24 swap or something else?

[christoph]

no - i am working on a M138/F136 swap

[MX-5RACER]

Sadly, there is no correct answer other than telling you to wait until you get the engine in place so you can finalize the routing, avoiding fuel lines, etc. Without having the engine and all the other things in place like the fuel lines, etc. you are 100% wasting your time. You will either make them too short or too long.

The only other option would be to make a bulk head connection at the firewall to finalize your routing inside the car, but you would still need to have everything in place to route the wiring in the engine bay.

[christoph]

Hi - well as soon as i have determined how long the cable to the cranksensor is - the first sensor after the firewall i can measure all the other connectors from there. It is a fairly simple wiring harness - i only want to controll the engine - for now i am planning 120cm from ecu through firewall to cranksensor - potentialy too long /depending on where i make the hole through the firewall - have you got any experience on how long this measurement is on average ? BR C

[RongTurnRacing]

Originally Posted by christoph

Hi - well as soon as i have determined how long the cable to the cranksensor is - the first sensor after the firewall i can measure all the other connectors from there. It is a fairly simple wiring harness - i only want to controll the engine - for now i am planning 120cm from ecu through firewall to cranksensor - potentialy too long /depending on where i make the hole through the firewall - have you got any experience on how long this measurement is on average ? BR C

The problem with that thinking is that it's not how our wiring harness works. The ECU side of the harness goes to a junction point at the passenger side of the engine and then the engine harness joins from there. Then you have the idea that the crank sensor is the same design between two completely different engine designs. On the FA20, the crank position sensor reads the reluctor wheel on the back of the engine. Is that now the engine you're going to use works? I know that engines like the LS have that wheel on the front of the crank rather than the rear and a 4 cylinder Boxer engine is a lot shorter from front to rear than a v8 engine.

The more I read this thread, the more I wonder what your actual starting point is. Do you have a rolling chassis without any wiring or something?

[christoph]

i know that the cranksensor of my new engine i gonna swap in is very close to the firewall - i am only planning to controll the engine - no other funciton of the factory ecu - i believe if you keep the std. ecu/engine harness you can recover various functions too like abs and power assisted steering - but if not than i don t care too much - so ya my pdm is gonna control next to ignition the fuel pump and the radiator fan and thats it

[RongTurnRacing]

Originally Posted by christoph

i know that the cranksensor of my new engine i gonna swap in is very close to the firewall - i am only planning to controll the engine - no other funciton of the factory ecu - i believe if you keep the std. ecu/engine harness you can recover various functions too like abs and power assisted steering - but if not than i don t care too much - so ya my pdm is gonna control next to ignition the fuel pump and the radiator fan and thats it

OK, I see. So, the engine harness is just that. An engine harness. The ECU is the Engine Control Unit so the wiring from it to the junction on the rear of the engine is still only controlling the engine. The other control modules such as the Body Control Module and SRS Airbag module are not wired through that junction. They appear to be accessed via CAN Bus and you will still be able to retain those items if you choose a good ECU solution. Personally, I run a Link G6 GT86 since it's plug and play. The up side for something like that for your setup is that since the FA20 technically has a total of 8 fuel injectors, you would be able to run your new engine with it. If you're planning on doing something completely custom then you are probably in for a lot of pain and you're probably not going to find anyone on this forum that can really help.