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Question on where to splice when using a bulkhead firewall connector

Practical Motorsport Wiring - Club Level

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Just finished to Club level wiring course (great stuff). Ive decided to re make my engine loom again after taking the course due to the fact that I now have the knowledge to vastly improve on my first attempt.

My question is about splices for sensor grounds, 5v and 12v supplies. When using a motorsports bulkhead connector should these splices be placed on the engine bay side instead of at the ecu connector?


G'day Bob.

In that situation, I'll often put the splice on the engine bay side of the harness to save pins on the bulkhead connector. The deciding factor will be the length of run from the bulkhead to the ecu, on the interior side. If this is getting any longer than around 300mm, I'll revisit the decisions, as wire sizes might need to be bumped up a notch to account for voltage drops, which can have the knock on affect of then needing to re-spec the connector to fit the larger wires.

What bulkhead connector were you thinking of using?

Hey Zac,

havent gotten quite that far yet. Still in the planning phase. This is going in a MKIV Supra so the run from the passenger kick panel to the bulk head would probably be slightly more than 300mm. All the wire in my current harness is 18awg and based on you lessons it’s overkill.


does trigger wire shielding typically end at the engine side of the bulk head? Then just non shielded from the bulkhead to the ECU?


You would traditionally continue the shield as close to the ECU as you can. When you get to the bulkhead connector, put the shield through on its own pin, (use something like this: https://prowireusa.com/p-1922-shield-terminator-with-22-gauge-lead.aspx )

Pick the shield up on the other side, with another of the same solder sleeve then continue to run to the ecu.

Ground the shield ECU side to the corresponding pin on your ECU.

Rob is on point here, that's exactly how I do it :-).

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