Electrical Cable Size and Colours

If all the cables were the same colour and size, it’d make the car very difficult to steal and very easy for the warehouse manager to keep stock.

Of course, there are other priorities which can be boiled down to costs of manufacture, operation and maintenance that make us makes one go the extra mile in the specifications of the electrical system. As the base material of cables, the copper, is now a relatively expensive commodity one automatically tries to keep the cable size as small as reasonable for the application.

Automotive cables are made of several to many strands of finer wire, each typically 0.20mm to 0.30mm in diameter which allows the cable to make tight turns easily. But a thick cable is still a thick cable and keeping the bulk of the cable small helps at the time of assembly and subsequent maintenance.

The necessary cable size is determined by the maximum electrical current that the cable has to carry, without overheating. The size is expressed as the cross-sectional area of actual copper in the cable, in mm² (square millimetres).Designers also have to take into account the voltage drop from the power source to the consumer for the current travelling through the cable. This can be calculated from the cross-sectional area. However, the total voltage drop is often substantially determined by the contact resistance in electrical connectors.This table is a rough guide to appropriate cable sizes for automotive, thinwall insulation (FLRY) cable. Note that the capacity has to be de-rated when multiple cables are bundled, as they often are in e.g. a wiring loom.Up-rating of cables is possible in some circumstances where the duty cycle is small. Applications such as window-winding, which (without children) take less than a minute out of every hour of vehicle operation, have a low duty cycle. Flashing turn indicator lights less so.

Similar de-rating is possible if the cable length is short and/or if there are adequate heat sinks nearby.

Copper mm² Current max O.D. mm Copper mm² Current max O.D. mm
0.35 7 A 1.3 7.0 57 A 5.1
0.5 11 A 1.7 8.5 63 A 5.6
1.0 16 A 2.1 10 70 A 6.1
1.5 20 A 2.3 16 110 A 7.5
2.0 25 A 2.7 16 110 A 7.5
2.5 29 A 2.8 25 170 A 9.5
3.0 33 A 3.4 35 240 A 11.0
4.0 39 A 3.5 40 300 A 11.8
6.0 50 A 4.2 40 300 A 11.8

Cable sizes above 10 mm² are generally considered to be “battery cables” and often have reduced ambient temperature limits such as -40°C to +90°C instead of the higher +105⁰C upper temperature of the smaller sizes.

Always make sure that the temperature specifications of the cable suit the lay of the cable. Short length of cable potentially exposed to intense heat can be fitted with protective sleeve, insulating the cable or even reflecting radiative heat. Copper is a good conductor of heat so it will carry it away to a cooler place. Insulation is however more problematic as most insulation material are good aborbers of radiative heat.

When one is upgrading/updating the electrics of an existing vehicle, the connectors often determine the cable sizes as the connectors still have to plug into the existing electrical devices.

One practical aspect to keeping fewer cable sizes is that it allows for larger quantities of the same crimp connectors, insulators, etc, all of the same size to be stocked. If the cable lengths are short, then the cost and weight differences in going up to the next size are insignificant; especially for sizes of 2.5 mm² and less.

This chart shows the colour and stripe combinations for each cable size, as used in the initial mapping out of the first 126 current tracks of decentralisation. The new colours that became available for automotive cables over the past 30 years are shown as fresh options for new wiring.
Cable Colours and Sizes

This is where each is used. It’s not complete and probably contains a few errors. Some of the cables are (so far) only used in one place at a length of a few centimetres. There may well be some rationalisation!

Colour Stripe Size Signal
Black (sw) 0.35 Supply voltage.
0.5 Supply voltage. Small signal.
1.5 J-Central to N/15. N/15 to N41/4
2.5 J-Front to J293/2
25 Battery A/+ to Starter B/30
Yellow (sw/ge) 0.5 D/X to J-DC
1.0 J169/14 supply via J-Central
White (sw/ws) 0.35 MFA switch J-InstAux to J119/17
Brown (br) 0.35 Chassis and Chassis return
0.5 Chassis and Chassis return
1.0 Injectors N30…N33. Cylinder Head (12) to Engine Loom (85)
1.5 Fuel pumps and J-RBody. N30…N33 common, J169/13 to battery A/-
2.5 J293/2 to J-Front
4.0 (119) common to battery A-, V2 to (80)
6.0 J293/4 to (119)
Black (br/sw) 1.0 J169/19 to (18), Lambda G39 to (18)
Yellow (br/ge) 0.5 J-RBody to V-FFlap. J-DC to F9. J-Front to G17
1.5 J169 to N30…N33
Red (br/ro) 0.5 S Contact D to J-DC. Coolant level G32 to J-Front
Green (br/gn) 0.5 J-Central to J169. J-Central to coolant temp. G62
Blue (br/bl) 0.5 Fuel gauge G to J-RBody. J-Central to brake fluid level F34
1.0 J-Central to G70
White (br/ws) 0.35 E109 to J-DC, J-InstAux to J119
0.5 J169 to J-Central. J-Central sensor common; G40, F81/F60, G62
1.0 G70 to J-Central ??
1.5 A- to N41
Red (ro) 0.35 J-InstAux J119/11
0.5 J-DC to D/30
1.0 J-Front to F18/3. N30…N33 common.
4.0 J-Front to starter B/50. J-HVAC to V2
6.0 J293/1 to Fuse SA2
16 Alternator C/B+ to B/30
Black (ro/sw) 0.5 J-DC to D/50. J169 to J-Central. J-Central to G40/+. N to INSTRUMENTS
1.0 J-Front to F18/1. J-Central to G39/3
1.5 N41 to N. J-Central to Supply N30…N33
Yellow (ro/ge) 0.5 Common supply G23+G6J-Central to J169/3
1.5 J-Rbody to common G23+G6
Green (ro/gn) 0.5 J169/1 to J-Central
Blue (ro/bl) 0.5 J169/11 to J-Central. J-Central to F60+F81
White (ro/ws) 0.35 J-InstAux to J119/9. J-DC to E86/2
0.5 J-Front to B/15a
1.0 J-Front to F18/2. J-Central to G39/3
Green (gn) 0.35 J-InstAux to J119/24. J-Central to J169/16. J-Central to J169/10.
0.5 Sx to J-DC. Sx to J-InstAux.
1.5 J169/25 to N41/6
2.5 J-Front to J293/3
4.0 Sx to supply common (J-DC+ …)
Black(gn/sw) 0.5 J-Front to G8
Blue(gn/bl) 0.5 (engine speed) J-Central to J-Front
White(gn/ws) 0.35 J-InstAux to J119/6
0.5 J-RBody to VFFlap. J169/18 to J-Central. J-Central to G40/o
Blue (bl) 0.35 J-InstAux to J119/16. J-InstAux to J119/21
1.0 J-Central to G70/5
6.0 Sy to J-HVAC
Black(bl/sw) 0.5 J-Front to F22
Brown(bl/br) 0.5 J-Central to F34
Red(bl/ro) 0.5 J169/21 to J-Central. J-Front to G32
Yellow(bl/ge) 0.35 J-DC to E109/3
1.0 J-Central to G70/2
White(bl/ws) 0.35 J-InstAux to J119/25. J-InstAux to J119/1
0.5 J-RBody to V-FFlap. J-Central to J169/9. J-Central to J169/17
Yellow (ge) 0.35 J-InstAux to J119/8
0.5 J169/22 to N71/1. J-Front to F1. E9 to J-HVAC
6.0 SA1 to J-Front
Red(ge/ro) 0.35 J-InstAux to J119/23. J-DC to E109/4
0.5 J-Front to G2
Violet (li) 0.35 J-InstAux to J119/2. J-InstAux to J119/7. J-InstAux to J119/19
0.5 J-Rbody to V-FFlap
Black(li/sw) 0.5 J-RBody to G/1
White(li/ws) 0.5 (LIN) J-RBody. J-Front. J-InstAux. J-DC
Grey (gr) 0.35 J-InstAux to J119/12. J-InstAux to J119/4
0.5 D/P to J-DC. J-InstAux to K7
Blue(gr/bl) 0.5 J-HVAC to L16
White (ws) 0.35
0.5 J-RBody to V-FFlap. J169/23 to N71/2
Red(ws/ro) 0.5 J-DC to F9
Yellow(ws/ge) 0.5 (car speed) J-InstAux to J-Front

Some of the required lengths (so far) are only a few centimetres. A Bill of Materials of cabling will have to be reviewed before ordering and make an acceptable compromise between maintaining “factory standard” colours for cables and ordering reasonable quantities.

The same, but non-standard colour may be acceptable for connecting nodes in close proximity to the connected devices.

In the case of J-InstAux, most of its connections are into the one connector of the instrument cluster. That’s because it’s the network interface to the instruments. It may be possible to construct the node so that it plugs directly into the cluster’s connector.

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