Wiring harnesses for the 1UZ-2UZ-3UZ engine conversions seem to fall into two categories: (a) modified OEM harnesses like those supplied by Gloverman (of this Forum), or (b) expensive but amazing works of art like those supplied by Chris at Phoenix Engine Management. But I'm wondering if there might be a middle ground option as well: building a new harness using new terminals and connectors where necessary, but using common thin-wall automotive cable instead of race-spec TE "Spec 55" MIL-W-22759/32 wire?
I'm not building a race car, so buying or building a race-spec wiring harness seems like overkill. (See: Motorsports ECU Wiring Harness Construction) OEM-quality should be fine. But, what type of wire does Toyota/Lexus use in its OEM wiring harnesses?
The aftermarket automotive cable available in the UK mostly seems to be PVC-insulated cable (aka GPT) made to ISO 6722-1:2011 (Class B), rated up to 105ºC with "excursions" up to 120ºC. It is commonly available in ten solid colours (at least in the smaller sizes) with up to ten "striped" or "tracer" colours also available for each of these. That makes it very useful for mimicking OEM wiring colours (especially when compared with Spec 55, which is (most easily) available in any colour you want--as long as it's white!) My current favourite supplier in the UK is ALM Solutions, but it is also available from Altec Automotive, Kojaycat, ECS, Auto Sparks, 12v Planet, Car Builder Solutions, Polevolt, AES and Vehicle Wiring Products.
The automotive cable most available in the US (TXL) seems to be XLPE-insulated cable made to SAE J-1128, rated up to 125ºC. There doesn't seem to be much crossover across the Pond between PVC and XLPE, but Eland Cables in the UK does have some information comparing them: FAQ: The benefits of XLPE insulated cables | Eland Cables.
(For reference, "Spec 55 wire is insulated with modified radiation cross-linked ETFE polymer. It has a temperature rating of -65°C to 200°C continuous using a silver plated copper conductor". It also costs 3-4x as much as PVC-insulated cable... Considering a UZ wiring harness uses around 300m of cable, that difference is significant.)
In the real world, there probably isn't much difference between PVC and TXL, although TXL seems to have somewhat better heat resistance (and PVC is readily available in the UK in approximately 100 solid/stripe colour combinations, which is nice).
True, Spec 55 is rated for much higher temperatures than either PVC or TXL, but most of the cable in a custom automotive wiring harness will be enclosed in a protective sheath of some kind, such as the traditional race-spec 2:1 Raychem DR-25 heat-shrink tubing, which has an operating temperature range of 75°C to 150°C. (The standard DR-25 alternatives are 4:1 Raychem ES2000, which is rated for -40°C to 130°C, and 2.5:1 Raychem SCL, which is rated for –55°C to 110°C.) Excessive heat really should not be an issue at the ECM end of things, and the other end can be sealed with moulded boots/RT-125 epoxy on Deutsche DTM connectors, so, sheath your PVC cable in DR-25 and it should be protected pretty well, no?
Ciao,
JZH
I'm not building a race car, so buying or building a race-spec wiring harness seems like overkill. (See: Motorsports ECU Wiring Harness Construction) OEM-quality should be fine. But, what type of wire does Toyota/Lexus use in its OEM wiring harnesses?
The aftermarket automotive cable available in the UK mostly seems to be PVC-insulated cable (aka GPT) made to ISO 6722-1:2011 (Class B), rated up to 105ºC with "excursions" up to 120ºC. It is commonly available in ten solid colours (at least in the smaller sizes) with up to ten "striped" or "tracer" colours also available for each of these. That makes it very useful for mimicking OEM wiring colours (especially when compared with Spec 55, which is (most easily) available in any colour you want--as long as it's white!) My current favourite supplier in the UK is ALM Solutions, but it is also available from Altec Automotive, Kojaycat, ECS, Auto Sparks, 12v Planet, Car Builder Solutions, Polevolt, AES and Vehicle Wiring Products.
The automotive cable most available in the US (TXL) seems to be XLPE-insulated cable made to SAE J-1128, rated up to 125ºC. There doesn't seem to be much crossover across the Pond between PVC and XLPE, but Eland Cables in the UK does have some information comparing them: FAQ: The benefits of XLPE insulated cables | Eland Cables.
(For reference, "Spec 55 wire is insulated with modified radiation cross-linked ETFE polymer. It has a temperature rating of -65°C to 200°C continuous using a silver plated copper conductor". It also costs 3-4x as much as PVC-insulated cable... Considering a UZ wiring harness uses around 300m of cable, that difference is significant.)
In the real world, there probably isn't much difference between PVC and TXL, although TXL seems to have somewhat better heat resistance (and PVC is readily available in the UK in approximately 100 solid/stripe colour combinations, which is nice).
True, Spec 55 is rated for much higher temperatures than either PVC or TXL, but most of the cable in a custom automotive wiring harness will be enclosed in a protective sheath of some kind, such as the traditional race-spec 2:1 Raychem DR-25 heat-shrink tubing, which has an operating temperature range of 75°C to 150°C. (The standard DR-25 alternatives are 4:1 Raychem ES2000, which is rated for -40°C to 130°C, and 2.5:1 Raychem SCL, which is rated for –55°C to 110°C.) Excessive heat really should not be an issue at the ECM end of things, and the other end can be sealed with moulded boots/RT-125 epoxy on Deutsche DTM connectors, so, sheath your PVC cable in DR-25 and it should be protected pretty well, no?
Ciao,
JZH
