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SR22VET MILSPEC harness construction questions

Practical Motorsport Wiring - Professional Level

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Hey all!

i just had a few quick questions while im building the documentation and planning of my personal harness for my project! im using this project to test my skills by OVER doing this harness, budget isnt really an option as its going to be for MY build,

everything will be terminated with AS and ASU connectors, i just had a couple of questions regarding the wire size

in the practical construction of the FD3S harness Zack was mentioning for cooling fans that instead of running a 14AWG wire to the fans you could split the load into 3x20AWG tefzel wires all pined to the power pin of the fans, i can see the sense behind that, id just like to get some more light shed on that process,

my understanding for the reason of doing this is because of the fact most AS connectors share the same size contacts through out that whole receptacle, now would you ideally run the 14AWG wire on the cabin side and terminate it to 3x20 AWG wires behind the bulkhead then pin those 3 through the receptacle and out to the fans? seems like the most logical way in my mind,

i've chosen to go with the AS 100pos connector for my bulkhead, which uses size 20 contacts IIRC,

ill be using r35 coils and ID injectors, would 20awg tefzel be good enough for the power supplies to these items? ive got about a 3ft span from the bulkhead to the coils and injectors, each power supply will be coming from the bulkhead where in the cabin itll be supplied by more likely a 16AWG (if this is the correct way to do so)

also because this is a "street" car, ill need to run high and low beams as well, could i get away with a single 20AWG conductor to power each headlight (factory HIDS, IS300 if that matters) or would i be better off running 2x20AWG for each headlight?

sorry if this sounds noobish or confusing! just wanna get the correct answers before i start my final plans!


There are pros and cons either way, but generally for high powered stuff your proposed method of using a single 14awg through the majority of the loom then spliced out close to the connector and passed through 3 pins is actually better than Zac's example of using 3 separate 20awg wires. With 3 separate wires, if one fails or has a bad crimp or whatever then you suddenly have 50% more current passed through the other two wires (and there is no way to know that one wire just failed since the other two will still be working at least until it all melts). Even if one wire doesn't fail you can still have a situation where if one has higher resistance than the other two then it will heat more and its resistance will further increase in a self-perpetuating scenario.

The downside of a single 14awg is bundle packaging and more splices.

"i've chosen to go with the AS 100pos connector for my bulkhead, which uses size 20 contacts IIRC"

Are you sure - the only 100pos I can think of is size 22 contacts?

A single 20AWG is fine for 4 high imp injectors. But I would probably split the coil power across 2 pins - if size 22 pins.

I have no experience with HID's to know what they draw, but usually the high beams are halogen unless it has projector lenses.

100% correct it is 100 position 22 contact, that is my bad, might have to rethink my strategy,

overwall I’m just trying to avoid having 2 connectors for coming into the bay, but seeing this I may have to rethink and do something similar to the FD, size 20 and size 22 contacts in 2 different connector,

as for the splitting to multiple awg, my theory was a 14 AWG for said cooling fan out of my PDM up to my firewall bulkhead where I’d then terminate to 3x20awg to continue the short 3ft run from the engine bay bulkhead to said cooling fan,

not 100% opposed to having a connector of size 22 contacts for the low current ins and outs, and a second connector which is try to find an option to have mostly size 20 and maybe 1-4 size 16 contacts ( or 14 ) for the heavier stuff. Just trying to weigh my options, you make some valid points about having 3x20awg conductors instead of 1 14awg