Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

coil and Injector power wiring

EFI Wiring Fundamentals

Forum Posts



Tech Articles

Discussion and questions related to the course Motorsport Wiring Fundamentals

= Resolved threads


I'm going to re do some wiring on my Celica gt4 as a quick fix to get the car running has over stayed it welcome.

I'm running a link g4+ plug in ecu for my st205 celica, last year I converted to coil on plug and while I was making he loom I just used the 12v feed that used to go to the original ignitor and the ground goes to the intake manifold.

While I was building the first loom a friend told me that I should have run the power feed to the coils and the injectors from the main efi relay as on the celica the injectors are powered after the ignition key and don't see the same voltage as the ecu so effects dwell times and such. Is there any truth to this as I'm looking to make up new sub looms for the coils and the injectors to tidy things up and it would be the best time to sort out the power feeds.

any help/info is appreciated.

What coils? Can you draw a diagram (MS paint or whatever) of how its wired now and this other configuration you are thinking about?

G'day Adrian.

Page 314 and 315 of the FSM should give you the info as to what's going on:


The ECU gets its power from the main EFI relay, whereas both the coils and injectors are indeed powered directly from the ignition switch. As long as your ignition switch is in good condition and making good contact, you're not going to see much of a drop across it, so it shouldn't be a problem. Your COP setup will probably be drawing a similar current overall to the original single coil distributed system, so the OEM fuse sizes will still be appropriate.

Are you running the OEM injectors, with the resistor ballast pack still?

I wouldn't power the injectors and coils from the main EFI relay, as the OEM wiring and fuses feeding the relay wont be sized for the extra load, but if you think the OEM setup is causing you problems, you could absolutely add in to two relays, one to power the coils and one to power the injectors.

Post up some details of your car, I love me an ST205 :-).

Thanks for the reply, and i will post uo some info on my car in the morning

I'm running high impedence top feed injectors with the ballast bypassed. I'm just looking to make a better loom for the coils and while I'm at it I thoutho I'd look in to what my friend said about the different circuits.

If you're doing some re-wiring anyway, I'd take the time to add in extra supply relays and fuses for the injectors and coils, it'll give you more flexibility down the line too if you modify things further.

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?