Use a universal harness kit or construct a loom from scratch?

Hi

I've just completed the EFI wiring fundamentals course and found it extremely helpful. Well done on the great content and thanks.

I will be soon be embarking on installation and wiring a Haltech Elite 1500 on my series 3 Mazda RX-7. This is what HP Academy would describe as a modified street or club level car: 13B turbo, around 300-400rwhp with standard interior and full factory road features (AC, cruise control etc).

I'm currently debating whether I purchase the ECU as a kit with the Haltech universal premium wiring harness. This looks to be very good quality, with fused relay box, pre-wired for the critical ECU power etc, firewall grommet, braid and flying leads. But it comes at an additional price - around AUD400 at the time of purchase.

If I'm building a harness at the modified street/club level, the question is whether I use the universal flying loom kit as my starting point, or just buy the terminals, wire etc and build from scratch. I figure this comes down to (a) cost (can I buy the same components for less than AUD400); and (b) whether I can significantly improve upon the design and construction of the Haltech loom for the same cost. For example, the Haltech relay/fusebox might not have enough slots to cover all the relays and fuses I require for my outputs, so I may need to wire in a second one. Maybe some of the power wires aren't sufficiently big enough?

Assuming the universal loom is a good starting point, the next question is whether I would significantly benefit from the club-level advanced course. Most of the power circuits in the universal loom appear to be there already, and it looks like I might be able to apply the knowledge and skills from the EFI wiring fundamentals course to complete the harness for my application. This is hopefully going to be the only harness I ever build, so the advanced course is a bit of an investment if it goes beyond what I need.

Any insight or guidance would be greatly appreciated.

First thing may be to check what functions are integrated with the factory ECU, what would be covered by the new ECU and what, if anything, is going to be a problem.

Second thing is to balance up the cost of the universal loom Vs the costs, and hassles, of sourcing your own loom parts.

G'day Greg. Series 3 RX7? Love it, post pics :-).

I'd say the Haltech harness is going to be a very good starting point for your project. You'll need to go through the power supply design stage for your project though to know if the haltech harness will have all the required relays and fuses you'll need. I'm not familiar with them myself, but AUD400 sounds like a pretty good price if it includes the relays, fuses, mountings, etc... You'll also not be left with a lot of excess materials, if this is the only harness you think you'll be building.

As much as I want to say YES, buy the course, I suspect it might not help you out too much. I will say though that we have a 60 day money back guarantee, so if you purchase it, watch it, and think it wasn't worth the investment, you can get your money back :-).

S3 is factory carb (other than 12at) so it is all pretty basic Gord.

Even if you have to run a couple of extras or tie back into the factory relay triggers/repurpose a couple of power supplies in parallel with the haltech loom it would still save money and I suspect a lot of time compared to assembling an entirely new fuse box and relay set for the car.

Thanks gentlemen for the great replies. Very helpful.

I've taken the time to closely review the wiring diagrams for the Haltech constructed looms in detail and they look to be very good. They have shielded wires where required, branches for sensor and output power and ground wires etc. Having compared to just the basic cost of wire and taking into account time saving, it looks to be good value.

Slides is right in that the factory functions are pretty basic. In reality the only factory wires that need to interface with the ECU harness (apart from power circuit for the ECU itself) are A/C and vehicle speed sensor from the speedometer (from factory cruise control). Everything other input and output I'm using is bespoke.

The other factor I didn't mention is that my fuel system is vapour LPG, delivered via a carburettor/throttle body mixer. The unused injector outputs will be reconfigured as auxiliary outputs. Some of these outputs will require some thought around power supply and relays, but looking at the wiring diagram, they should be easy enough to integrate.

Zac: I've attached some photos. If you're interested, I have a 40 page build log going back to 2006 here: http://www.ausrotary.com/viewtopic.php?f=21&t=89142

I'll be sure to update here when I'm to wiring. I am also going to neaten up and do a engine bay wiring tuck for the factory wiring harness (for lights etc). After going through the fundamentals course, I can see how the same skills can be applied to that task and I now feel a lot more confident tackling the job.