Where should I run a standalone LS harness into the cab of a 72 without drilling new firewall holes?
Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.
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- E38 ECM; Chevrolet Performance NA LS control kit 19171935; LS2/LS3/LS376/LS7/LSX454; 58x/4x; 2006+: E38 ECM is sealed and underhood-safe but must avoid heat and splash. (Chevrolet Performance)
- E67 ECM; Chevrolet Performance LSA E-Rod control system 19299067; LSA: E38 connectors use slider-bar latches. (Chevrolet Performance)
- 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: PCM mounts inside the cabin through a 2-inch firewall hole. (PSI Conversion)
- Gen III PCM; Aeroflow AF49-1505; LS1/LS6; DBC; 4L60E/4L80E: Starter uses large black ring terminals; heat-sleeve wire under the manifold. (Aeroflow Performance)
- Gen III PCM; Aeroflow AF49-1505; LS1/LS6; DBC; 4L60E/4L80E: Harness splits at the firewall grommet into engine and underdash sections. (Aeroflow Performance)
Confirm against the instructions for your exact parts before wiring. More: Harness and power in our tuning guide.
Use the stock wiring harness hole in the firewall or the unused clutch linkage hole; both get the harness into the cab without drilling. In the builds we've seen, tucking the whole ECM inside the cab, for example in a mount near the glove box, is the usual choice rather than passing only the gauge and ALDL wires through. A PSI standalone harness comes with its own grommet for the pass-through.
Check this first:
- Check whether your harness includes a grommet (the PSI harness does)
- Make sure the hole edges are protected so the loom can't chafe
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead tuner (20 years of LS tuning). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.
Go deeper
Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| Dorman 8-pin Metri-Pack 150 connector (unverified lead) | 926-309 (not independently verified) | Some LS engine harnesses | varies | parts stores | Unverified Confirm pin count/series before ordering |
| Aptiv / Delphi Metri-Pack 150 connector shells and terminals | varies | OEM-style repairs | about $1-5 per shell | Mouser, Waytek | Current production Match series and pin count |
| Generic 16 AWG automotive wire | n/a | Main engine-harness runs | about $10-20 per spool | parts stores | Current production Match factory gauge; don't go smaller |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.
Further reading
Related questions
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- Stock PCM vs Holley Terminator X for an LS swap
- How do I tune an LS swap? (HP Tuners basics)
- How to make a standalone LS wiring harness
- VATS delete: what it is and how to do it
- Drive-by-wire vs cable throttle for an LS swap
- LS Series Engine Control System Guide — Chevrolet Performance (via Scribd)
- https://es.slideshare.net/slideshow/har-1019-vortec-swap-wiring-harness-instructions-efi-conversion-fro/47382494 — PSI Conversion
- https://www.crateenginedepot.com/pdfs/lsa_e_rod.pdf — Chevrolet Performance
- https://aeroflowperformance.com/pub/media/Instructions_PDF/AF49-1505.pdf — Aeroflow Performance