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Common Source wiring.

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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So ....

Your ecu has limited ground, one 5v one 8v etc pin and now you got lets say 8 things that need to be wired to the harness, where do you branch these wires from? The ecu pin is not very thick so I dont think 8 to 10 sensors or outputs can be crimped into one terminal. Soldering is discouraged so I cant run a long wire through the harness and solder every single branch to it either. So what do I do? How are multiple outputs and sensors connected to a common source?

Because everytime its told that this is a topic for another time in the modules and now I am stuck.

If you can't run a common wire, run the ground to a common point. So run multiple wires to the same common place.

It's not uncommon to run into this situation in motorsport wiring. I typically do my breakouts near the connector end. I have one wire from the ECU voltage source go into a splice with anywhere from 2 - 10 breakout wires, if that makes sense.

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You'd be surprised at how little current is required to run 5v sensors. Before you reinvent the wheel find out what the ECU can support and what the draw is for each sensor.

G'day Falah.

You're bang on that limited sensor supplies and grounds are a sticking point when building a harness, it can be a real pain in the backside.

I'll set up a little example here that will hopefully help. Let's say I'm wiring in a Link Monsoon ECU, and I need analogue sensor supply/grounds to Throttle Position, Fuel Pressure, and Engine Oil Pressure sensors. Along with sensor grounds to an Engine Coolant Temp, and Intake Air Temp sensors.

The Monsoon only has one +5V sensor supply pin, and one sensor ground pin, but we need three sensor supplies and five sensor grounds!

For the sensor supplies, I would crimp a short section of wire, say around 50mm, to the ECU header plug pin, and then use an open barrel splice to split this off into the three wires that head off to each sensor. This does mean that you are now running three wires through your loom that are all basically doing the same job, which can be a pain, but it means there is only a small section of wire (that ~50mm) which is carrying the supply current to all three sensors, so the drop across it will be really, really small. This will minimize the effect any sensor's varying load has on any other sensor's supply.

For the sensor grounds, I'd approach it exactly the same way, a short section of wire from the ECU header plug, and an open barrel crimp out to the 5 required wires, heading off to each sensor. I'd stagger the location of this splice though, so its around 20mm away from the sensor supply crimp. You don't want all your crimps on one place, as things get really bulky really fast.

The other benefit I see in doing it this way, is that you reduce the number of crimp splice connections you have in your loom in total, so there are less potential points of failure.

I hope that helps you out. I'm currently working hard on a re-format of the wiring fundamentals course, and you can 100% count on there being a good section on reliably splicing wires as, in my opinion, its the hardest part, and most common point of failure in performance automobile looms.

Zac.Peterson even though i already understood (and agree with you) your technique, that was an excellent write up and tutorial on exactly what needs to be done. What exactly about the wiring course will be changed? I recently purchased and it's not as in depth as i would have liked. I would love there to be an 'advanced wiring' course :)

Also for OP, Zac nailed it. That is the correct way to do it reliably and easily.

G'day Josh.

Just more of everything really, definitely more in depth, more b-roll demonstrations while I'm explaining things for sure.

Once the basics course is sorted, and there is at least one complete worked example in the bag, we're absolutely doing an advanced course focusing on high level motorsport techniques. Can't wait to get into that!

the content of the first revision of the course seemed light on so i didn't purchase it.

will the basic be updated to include alternator and kill switch wiring or will that be included in the advanced? this would be a draw card for myself, also info on ground loops.

Joshua: There is a big focus on the grounding side of things, as its the most common source (pun intended) of electrical mishaps in the performance aftermarket I reckon.

I hadn't thought about putting in anything specific about alternator and kill switch wiring, but its a good idea. I'll put it in the notes for the practical course. If you've got any questions on that though, post em up and we'll help out :-).

Alternator wiring has my curiosity too. I had my car wired twice and none of the time did the guys wire the alternator properly so the battery recharges. It ran flat in the middle of a busy road, making me look like a junk guy. Those guys werent good enough to even understand why the car was suddenly draining too much battery after going stand-alone.