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Wiring Miscellaneous Vehicle Accessories

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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What about the other accessories like wipers, lights, AC etc? How are they incorporated into the electrical system? Is the wiring for those systems run as a separate harness? I looked into my vehicle engine bay (Suzuki Grand Vitara) and the harness seems to include a lot more than just engine components. Everything seems to be included in or attached to a single harness.

It is generally easier, neater and cheaper to run all the wiring together, through common bulkhead fittings and cable routes - check out YT for some of the vehicle production videos and you will see how much difference thatcan make on fitting the harness into the vehicle, and consider what inventory costs would result from having only the specific harness for that specific vehicle's equipment level.

Often these production harnesses include terminations for accessories/equipment not used on all that vehicles product line so you will see unused plugs hanging from them. Depending on application and where the other end is used, you can sometimes use these for your own needs.

I understand that completely but specific to this wiring course no mention is made of including those additional components into the harness construction. I wanted to know how the wiring for those things like AC, lights, wipers etc would connect to the main engine harness.

When i do a re-wire or engine conversion. I find it generally easier to break it down into 2 parts. The engine stuff. And the vehicle stuff.

The engine stuff comprises of the ECU, the wiring run into the engine bay, and all sensors, injectors and coils etc. And anything related to the engine running like fuses or relays specific to the engine.

The vehicle stuff is everything that makes the vehicle work. Eg lights, wipers, blower etc, aswell as the key/igniton switchs, and also guages. Generally this is pretty basic on the cars I re-wire, as cars that get re-wired are either old vehicles with basic systems, or sport vehicles, again, with limited body functions. Modern cars with lots of body electrics, generally speaking, have electrics in better condition which dont need re-wiring, than say a 40 yr old vehicle getting a performace motor swap or something. Whic will probably need a full wire because of the age and extent of the mods.

As said, 2 seperate parts. Which will usually only meet and interchange about a dozen wires or so between them. And for the most part, i try and keep them seperate. Or another approach is to keep them seperate except for a shared relay/fuse board. Where everything meets and interchanges if it needs interchanging.

Thats just how I generally approach things. But every job is different. I dont think there is anything wrong with having a shared run if tge particular application calls for it. And i have done things that way in the past with great results. It really comes down to a case by case basis.

Now I understand. So you can wire the engine separate from the rest of the vehicle components without any problem.

I guess I need to start with one of those older vehicles with a minimum of components as a first wiring attempt. These modern vehicles look a bit too intimidating. I have nothing to work on yet unfortunately.

Thanks for your explanation.

Ah, I misunderstood your question.

Way I figure it is it may just come down to whether the ECU controls other functions - some more modern vehicles have it controlling power windows, waning displays, transmissions, HVAC, etc. If you can, I would suggest running two separate harnesses - one dedicated to the ECU and engine and what is needed to keep it going and a second for the rest of the vehicle's electrics. It isn't essential but I figure that it 'should' make chasing down wiring issues easier, simplifying that wiring design and build and, if required, a spare duplicate can be used to more quickly replace the installed harness if there is a problem - like a short during a race meeting or even a long distance race.

The courses focus on EFI Wiring, but there is a little cross over with OEM integration in the Practical Club Level course. Usually when you're modifying the vehicle, you want to keep the EFi wiring and Body wiring of the vehicle as separate as possible. However, I will say that with modern cars being so integrated, much like its becoming very, very hard to replace and ECU with an aftermarket item, its also very hard to separate out the wiring.