Wire to sensors or patch to OE harness?
 

I am in the process of cleaning up the Haltech wiring mess left by the previous owner of my '94 FD. I tried searching for a thread like this but had no luck.

My question is: do you all prefer to wire directly to the sensors and things under the hood or to patch into the OE Mazda engine harness?

I purchased both the Haltech flying lead and the original Mazda engine harness, so I have both to use.

I can see some of the advantages of each option. As far as patching in, a major one would be keeping more splices inside the car, away from the elements, but that can be counteracted with proper insulation. Another advantage would be brand new connectors :D. However, wiring directly from the ECU would definitely keep things simpler by removing the middle element between the ECU and the sensor. It would also provide the opportunity to make a custom harness to better suit a modified car. Since my car is rather modified, I am leaning towards the latter, but I could use some other opinions.

Some background on my car: I have no A/C, air pump, EGR, accelerated warm up, double throttle or sequential turbo stuff. Ignition coils have been relocated to the fender, so that's all custom wiring. The fans seem to have some kind of custom wiring setup. The car has a GReddy boost controller and Haltech wideband O2. I plan to add three Innovate gauges (AFR, boost, coolant temp).

In either case, it seems the transmission wiring from the OE harness must be preserved, but I would be weeding out plugs from the OE harness anyway, so modifying the harness does not concern me.

Actually, the way to do it is to source connectors and pins for all the various sensors, injectors, coils, etc, and wire them properly to the harness.

That way you avoid splices in as many circuits as you can.

You could have had Chris Ludwig build you a nice Mil spec harness with only the stuff you needed and add any additional sensor probably cheaper that the OEM harness.

Three options as I see it. One, use the OE harness with the Haltech patch loom. Two, do as Vicoor said and build a proper loom with the Haltech harness. We carry all the connectors you'll need. Or three, do as Mamba says and outsource a new custom harness.

Anybody doing rotary harnesses like the guys at Wiring Specialties do for Nissans and Toyotas?

I'm for Option Two, building a fresh harness that is tailor-made to your car's specific modifications and adding in a few logical upgrades. One thing I would suggest is separating the gauge senders', alternator and transmission/starter wiring from the stock Emission Harness, in the same manner as one would do on the S4 when wiring in a standalone.

You mean, like this? I know a guy...


Attachment 551951



Attachment 551955

Well that is top quality work. But i was thinking more along the lines of oem replacement harness, the milspec connector in the middle is a tad much.

Are those your harnesses Chris?

Yes. The mil-spec connector is optional.

Thank you, guys. This is much more feedback than I expected to get!

Vicoor and White Comet (or should I say, Ryosuke?), option 2 seems to be the winner so far. Since I have a fresh Mazda harness, I essentially have brand new connectors with pins and wires that I can splice into, but it seems like what you're saying is to crimp pins/female terminals onto the Haltech wires and insert them into the connectors (no splices). Is that correct?

C. Ludwig, those are some beautiful harnesses. I wish I had talked to you before purchasing the Mazda one, because I'm sure yours is less money, but built to a much higher standard and customized to the car's needs. Sounds like I could have just gotten connectors too.

Thanks for the recommendation. The alternator and starter wiring are part of the battery harness, though, correct?

What is the benefit of separating the sender wiring from the harness? Is it for running separate gauges? I am not familiar with the process on the S4.

Those look like top quality harnesses Chris, I have one of your direct fire harness and it's top notch. Next time I will have you build me a complete custom harness.

Would you be able to PM me a rough cost estimate for connectors and terminals? You probably know what I would need better than I do.

Here's a guess:

TPS
IAT
IAC
Injectors (4)
Knock (not sure if this is in use, actually)
CAS Trigger & Home
Coolant Level Disconnect & Switch (?)
Thermostat (I think these are a green and a black connector)
Fuel Temp
Transmission (3 connectors)

The image I am referencing was taken from here.

Email me. It's a lot less cumbersome than PMs. chris@lms-efi.com

I made the decision to purchase brand new connectors and run the Haltech wiring directly into them. Chris (C. Ludwig) is hooking me up with the complete package. Since my car is far from stock, I think this makes the most sense. Otherwise, I would be eliminating over 50% of the Mazda Harness and splicing into it. That just seems like a waste of a good wire harness.

All wiring is installed with new connectors, and everything works great. The hardest part was laying out the branches and getting everything wrapped up. Thanks again for all the help.