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Speartech LS 58x harness wiring: loose wires & fuses
A Speartech stand-alone harness plugs into the engine and computer; you only wire a handful of loose leads to the car. Here is where each one goes, from Speartech's wiring notes for the LS 58x harness.
4L60E / 4L80E harness
| Wire | Where it goes |
|---|---|
| Batt. @ starter | To full time 12 volt supply (positive battery post on starter, etc.) |
| pink / black | To switched 12 volt supply. Hot in key on, run, and crank. |
| gray | To fuel pump (+) terminal. From fuel pump relay; computer controls the on/off. |
| lt. blue | Brake switch / Torque Converter Lockup: hook to cold side of brake switch where it sees +12V when brakes are applied. Expects ground when brakes released, open circuit when applied. |
| white | Tach signal for electric tachometer. Ignore if not needed. |
| yellow | Speed signal for electric speedometer. Ignore if not needed. |
| orange / white | A/C compressor clutch. To freon switch or dash control. Computer does NOT control A/C during a swap; convenience wire for GM clutch only. Not present on all harnesses. |
| dk. green | Primary cooling fan relay control. PCM control of fan (ground trigger); wire to a relay. |
| dk. blue | Secondary cooling fan relay control. PCM control of fan (ground trigger); wire to a relay. |
Brake switch (light blue): Speartech says it must see +12V with the brakes applied, and ground with them released. With LED brake bulbs you need a 5-terminal relay; Speartech has instructions online.
Manual transmission harness
| Wire | Where it goes |
|---|---|
| Batt. @ starter | To full time 12 volt supply (positive battery post on starter, etc.) |
| pink / black | To switched 12 volt supply. Hot in key on, run, and crank. |
| gray | To fuel pump (+) terminal. From fuel pump relay; computer controls the on/off. |
| white | Tach signal for electric tachometer. Ignore if not needed. |
| yellow | Speed signal for electric speedometer. Ignore if not needed. |
| brown | Back-up lights (optional): take this wire to a +12V ignition source. |
| lt. green | Back-up lights (optional): to reverse light +12V input to bulb. |
| orange / white (older harnesses: dk. green) | A/C compressor clutch. To freon switch or dash control. Computer does NOT control A/C during a swap; convenience wire for GM clutch only. Not present on all harnesses. |
| dk. green | Primary cooling fan relay control. PCM control of fan (ground trigger); wire to a relay. |
| dk. blue | Secondary cooling fan relay control. PCM control of fan (ground trigger); wire to a relay. |
The manual-trans sheet lists dark green for both the A/C clutch ("now orange/white") and the primary fan relay; newer harnesses use orange/white for A/C. The A/C wire is only there if you asked for it when ordering, and the computer does not control A/C in a swap.
Fuse block
| Fuse | Circuit | Color printed on the sheet |
|---|---|---|
| #1 | Battery | orange |
| #2 | Injection and Ignition | pink |
| #3 | O2 heaters | brown |
| #4 | Fuel pump | pink |
Grounding and MAF placement
- Tie the battery negative, engine block, chassis and harness together. Don't ground to the valve covers; they are usually isolated on LS/LT engines. The block or heads are best.
- Speartech has seen bad grounds send all ground current through the harness and ECM and destroy both, and that is not covered by warranty.
- Most 58x harnesses use the LS3 MAF (4-inch tube) unless you ordered otherwise. Point the arrow toward the throttle body and give it at least 4 in. of straight tube on the filter side, or it can cause a no-start.
Other harnesses: Painless 60522 · Holley EFI. Choosing one: Tuning an LS swap.
Wiring questions
- Which factory wire do I tap for the ignition feed on a PSI standalone harness in a 1967 C10?
- Which standalone harness company should a first-timer use for a 5.3 DBW / 4L60E swap in a 67 stepside?
- What's the best wiring approach for an LM7 LS swap: stripped stock harness with stock ECM and fuse block, full standalone harness, aftermarket harness with stock ECU, or a standalone ECU?
- Can I DIY a standalone harness from a Gen IV E38 ECU for an LH6 5.3 swap, and how do VATS delete and speedo calibration work?
- My 1989 Firebird had factory VATS (Pass-Key) - do I need to do anything with the old system when swapping in a 2001 LS1 with a standalone harness and 2001 PCM?
Sources