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Starting from Scratch

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals

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Hey guys! I'm trying to start practicing the acquired knowledge on wiring but still same some (to say the least) doubts on tooling and materials to begin with. I'll start with a simple project of wiring accessories (spot lights, led bar, on board compressors, cooling fans, winch etc) in my own car but I'm having a hard time finding recommendations on "best bang for the buck" weatherproof connectors, wires, crimpers, tape, etc.

Do I need shielded wire for wiring the switches and power lines to accessories?

Do I have to sleeve all wires going outside of the car?

Is it really worth using milspec wire for this basic project?

What's a decent brand for weatherproof connectors? Or should even worry about using them? This won't be a baja car or race car but very humid/wet environment.

Any other thing that I'm missing on sourcing materials or jumping into this project?

Sorry for the somehow broad post.


For basic stuff like that you need a spool of wire, a good crimper, a soldering gun and solder, a lot of crimp terminals.

Consider a weatherpack kit, search for the starter kit.

You don't need shielding or mil spec for wiring up headlights, relays and basic switches. Anything like a crank angle sensor or ignition system will be sensitive to shielding though.

Thanks for the quick response. The Jegs kit looks promising. Any recommendations on wire brand? I'm thinking 14-10 gauge for power and 16 gauge for switches to make it more compact?. Locally there aren't options available besides speaker wire so I order everything online. Literally everything.


I would say 18 gauge wire is easiest to work with for unshielded stuff that isn't carrying much current. I don't have a particular brand, we can just get it at a hardware store.

G'day Jahir.

No, I wouldn't use milspec wire for this project, go for TXL insulated wire, its cheap and reliable. I get mine from

No, you don't need any shielded wiring here.

For connectors, weatherpack will be fine for your application, but Deutsch DT and DTP might be a bit more compact and reliable, but you will need specific crimpers for the terminals. This kit: is really bloody great and not badly priced. It'll cover 90% of your crimping applications, including weatherpack if you've already got some of those terminals.

Compressors and lightbars and such can draw quite a bit of current, you'll want to get the specs on this and make sure you size the wiring accordingly.

I'd sleeve any wires exiting the vehicle, yes. Another layer of protection is always good, plus it looks much tidier and more professional.

Hope that's helpful, let us know how you get on, post up some pics of what you're up to :-).

Thank you guys!

Waytek wire seems like a great source for supplies but the MOQ is kinda high. I've found which seels TXL and GXL not badly priced in smaller quantities. For sleeves and relays still Waytek is the way to go.

I'm still trying to decide whether I should go with many different colors for ease of troubleshooting in the future, or just stick with red and black.

Hey Zac, for some reason I can't open the link for the kit. Do you have a kit name that I can search for?

Yeap highest draw I suspect will come from the air compressor and it's around 20 amps. There will be 7 feet of wire from the fuses and relays to where it seats at the back of the car.

I yes, most definitely once I start putting everything together I'll try to document and post as much as possible B-)

Hey Jahir. Try searching for "Toolaid Master Terminal Service Kit 18700", should be able to find them that way :-).

i would stay away from weatherpac. i had nothing but issues and ended up replacing all of them for Deutsch DT and DTP ones. so much nicer.

Well just had my cart ready for other and I got a notification... UPGRADED WIRING COURSE AVAILABLE!!!

I'll be going over this new version while waiting for the supplies to arrive. Hopefully I'm not forgetting anything. I'll end up going with 18awg (as recommended) for wiring switches and 14awg for power lines.

@Zac Found it! That looks like a sweet kit for not a bad price (Amazon $114).

@Raymond is the Jegs weatherpack ($55) kit similar to the one they sell at DIYAutotune ($99) or the Delphi ($152) ones?

@Thank you Shane for the Deutsch recommendation. I know they are among the best brands out there but it may exceed the budget for the "practice build". I'll compare sorting individuals connectors instead of a whole kit and see how it stacks up.

I'll try to draw out a diagram on how I think things could go (wires,connectors,switch,fuses etc) and post it here so you guys can laugh a little.

Due to work and basically... life, this has taken more than expected to start but finally and unvoluntarily it has. I'm adding a picture of what I'm dealing with.

I want to get rid of all those postivie leads going to the battery terminals for which I will connect a single 0/1 wire (used) or buy new 4ga wire from the terminal to a fuse box for the power wires, from there these will go into mechanical relays actuated by a switch panel I will build inside the cab. For power wires I'll be using TXL 14ga and for switches 18ga TXL wire.

For now I don't want switches to bypass the ign switch as so I'm thinking on using a relay with ign switch signal to control the positive lead to the switches. Now, whether is a good idea or not, you tell me. It's either that or adding another switch to the panel for master power.

I do have a few questions before I start splicing and gutting this thing.

% Grounds... should I wire ground leads directly to chassis or should I go for the batt neg terminal? Some of the accesories like air compressor, lift pump etc are about 6 feet to the back of the car so I'm trying to avoid unnecessary wiring done.

%Should I use a fuse boxes for switches leads too?

%What's a good way to find a parasitic power draw? (the whole "project" got bumped up because after 6 days being parked, both batteries died. I use dual Optimas Blue Top 800CCA each. So I'm in the hunt for that issue while I clean the wiring.)

%Would these wire gauges be good candidates for concentric twisting? If so, where could I find a good guide to follow?

I think some of the supplies might be arriving this upcoming week. I'm already getting shipment notifications so... stay tuned.

Attached Files

G'day Jahir.

If you power the positive side of your relay switching coils (Pin 86) from the ignition switch, and have your control panel switched connect the negative side (pin 85) of the switching coils to ground, the relays will only operate when the ignition switch is on. If the ignition gets switched off, all the relays will also switch off no matter the position of their individual control switch.

You should be fine to ground the compressor, lift pump, etc to the chassis. You will need to make sure the ground strap that connects the battery negative to the chassis is in good condition, and making good electrical contact.

I would fuse the supply form the igntion switch that heads to your relay switching coils, yes. Take a single +12 ignition switched wire into a 5A fuse, and then break it out to all the relay coil positives on the other side, that way you only need a single fuse to protect all the relay switching coil wiring.

Finding parasitic draw can be a real headache. From the picture you've posted, you could be there for a long time tracing down all the modifications that have previously been made! To start though, you will need access to a current meter, or 'current clamp' that can read down to tens of milliamps. you then put the battery back in place, and with all the systems turned off, measure for any current flowing in any of the power wires exiting the battery. Once you find which wire the current is heading down, you can narrow down the search for the device that is drawing that current. If you find current flowing down the main power feed that heads to the fusebox of the vehicle, you can try removing fuses one at a time till the current draw stops, letting you know which circuit was drawing the current.

It's possible to twist any harness, but in this instance I wouldn't worry about it. I've never found a really good guide online, which is why I'm currently writing one for our professional motorsports wiring course :-).