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Secrets of British Wiring.

Coping with that rat's nest of faded and tattered wires under the dash and in the engine compartment of your prized Rover, MG, Jaguar, Hillman, Triumph or other examples of fine British automobilery, or meandering along the frame of your favorite British two-wheeler, can be irritating at best.
Some of you are fortunate that the original colors are still visible and so are easily traced.
The rest of you may not be so lucky.

Do not despair!

Even if you do not own a wiring diagram for your particular car, the following information may be enough so that you can properly connect, repair, or even make a new loom (or harness) to the manufacturer's exact coding. At least, you will be able to identify unknown loose wires.
Also included is a list of places where you may he able to get your harness repaired or replaced with an exact duplicate.

What's in a Loom?

Early wiring looms were covered with a black cloth wrapping interwoven with various yellow or other light colored tracers. Later ones were covered with black or other colored plastic tape.
In the construction of all looms, friction tape is used along the various legs, and at branch junctures to hold individual wires in place while the harness is being wrapped by a special machine.
There are usually three or four different sized wires to carry the current loads of various circuits. The most common sizes are: battery main feed (44 strands x 0.012" (appr. 5-gauge U.S.) - 22 amperes); generator main feed (28 x 0.012" (appr. 12-gauge) - 14 amperes); and other circuits (14 x 0.010" (appr. 16-gauge) - 5 to 6 amperes).
Other sizes include 37 x 0.036" (20-gauge) 0.68 amperes and 61 x 0.036" or 61 x 0.048" (18-gauge) - 1 ampere.
Note that the smaller the number in the American wire gauge system, the heavier the wire. Only these wire sizes were used on vehicles prior to 1967. After that, a number of additional sizes were needed to handle newfangled and sometimes more powerful appliances.

Color me What?

There were only seven basic colors used (solid, or with various contrasting stripes or tracers) during the early years (post-war to 1967). They were:
(1)  Brown - Battery circuit. From the battery or starter switch to the ammeter or voltage regulator (control box), and feeding light and ignition switches, and radio from control box terminal Al.
In addition, brown was the basic color used for leads from the starter switch to the electric clock, inspection lamp sockets and battery auxiliaries fuse (from which are fed the horns, cigarette lighter, interior lights, etc.).

(2)  Yellow Generator circuit. From the generator armature terminal to the D terminal on the control box, and to the ignition warning light.

(3)  White - Ignition circuit. This color is used for all (usually unfused) items that are powered up when the ignition switch is turned on - such as fuel pump, starter solenoid switch, overdrive, etc.

(4)  Green - Auxiliary circuits. All circuits fed through the ignition switch and protected with fuses or circuit breakers such as stop lights, turn signals, fuel gauge, wipers, etc.

(5)  Blue - Headlamp circuits. Fed from terminal S2 (or H) on the headlamp switch.

(6)  Red Side (park), dash and rear lamp circuits (some manufacturers used purple in their dash-light circuits). Fed from terminal S1 (or T) on the lighting switch. Included in these circuits are fog lamps and other lamps supplied with power only when the park lamps are in use.

(7)  Black - Earth (ground) circuits. Used for all devices that are not grounded internally.
Components of each circuit consist of three wires: the feed; the switch wire and the return. The return wire is not needed, of course, if the component is grounded directly to the chassis or through the body of the car, or frame of the bike.
Some variations in fusing, switching circuits, and so on were employed, but the three-wire principal is carried out through all vehicles. I must add, though, that since the introduction of solid-state technology, this last statement may no longer be true for all circuits and/or components. Feed or supply wires are always of a solid color. Switch wires have the main color of the feed wire, but with a tracer. Ground wires are always black.
Be especially careful when fitting wires to any component. Don't mix them up because not all circuits (especially lighting) are fused. One careless mistake could cause your loom to fry all the way from the component to the source of power when you switch on that errant circuit.
In fact, it is recommended that you install an in-line fuse holder (and appropriate fuse) in all circuits that do not contain a protection device. A convenient and out-of-sight mounting place can usually be found somewhere under the dash, or under the gas tank on a motorcycle. You will usually connect one end of the fuse holder to the switch and join the other end to the wire(s) that usually go to the switch. Fuses for headlamps should be 50-amperes, and for park, tail or license lamps, 35's.
When components are controlled with switches in the ground circuit (like most windshield wipers), the fact is noted by a wire that has a black tracer. You will want to keep a sharp eye out when playing with other wires in these circuits because they are "hot" ones, and some of them are not ever "dead" unless the battery has been disconnected.

What's in a Diagram?

Early British wiring diagrams are coded with numbers representing the color of a wire in any given circuit. Later schematics use only letters. If you run across a diagram that is missing the translation, there is a list of the codes for both systems near the end of this article.

Going it Alone

When you are trying to salvage or repair an existing harness, and you can't identify the color of a particular wire because of fading or deterioration, you can usually cautiously cut and peel hack a bit of the cloth wrapping to a point where it reveals a wire's true flavor. It you are careful, you probably won't ruin too much of the cloth wrap. It is a good idea to keep a needle and thread handy to prevent further raveling by stitching up the area you peeled back after you identity wires or make repairs.
If it becomes necessary to completely strip the harness of its outer covering, don't fret; there are several companies who will re-wrap it, just as it was. Mind you, don't fail to save a sample of the original pattern.

The English Connection

Most early British vehicles use an archaic method of connecting wires to their terminal points - they let you fuss with bare wires that have to be held in place while you run down a brass set screw to secure them. This operation can be made a whole heck of a lot easier even when you have as many as four or five wires to cram into the tiny space provided. The secret to beating this inconven-ience is in the proper preparation of the ends of the wires.
If you strip each wire the same amount i normally 4" to 3'8"), you can almost never succeed, except when you are dealing with only a single wire. When you get it almost tight, one or more of the wires will invariably squirt out from under the screw.
By stripping just a fraction more from each succeeding wire, no insulation can get under the screw as you tighten it. You can make a tidy "bed" of the copper, and so allow the set screw to clamp down on only the copper strands, as the insulated portions will automatically move to one side or the other.
Start your securing operation by making sure the loom is supported so that it has enough slack to allow all the wires you are working with to remain in position. If they seem too strained or too short, adjust the loom for a little slack in the area in which you are working, and tie it off with a piece of string so the wires can't move away from where they are to be connected.
If you wish, you may solder the batch of ends all together, inserting a heavy lead in the end of the pack to use as the sole wire to be trapped under the screw. All ends should be sparklingly clean before you solder.
In fact, for the best possible contact at any connection, you should make sure all wire ends are bright and shiny before you secure them.
After twisting each of the individual ends, remove the set screw and insert the wire that has the least copper exposed. Make sure that when the wire is fully inserted, the insulation clears the opening.
Then, carefully take the next two wires and slip them over the top of the first, letting the insulated portions find their own spots.
Follow with the balance of the wires in the same fashion and, while gently squeezing them from top one to bottom and pressing the ends of all of them toward the "hack" of the hole, insert and tighten the set screw. If you still have difficulty, you might try taping the wires together to help hold them in the right pattern while you tighten the screw.
Wiring is really easy if you pay attention to putting the right wire in the right place and remember, BLACK is always GROUND!
With these few hints and accompanying tables, you should be able to figure out where everything goes and how to deal with some of the mysteries of wiring.

Lucas / British Wiring Color Codes.

1.  Blue (U)
2.  Blue with Red (UR)
3.  Blue with Yellow (UY)
4.  Blue with White (UW)
5.  Blue with Green (UG)
6.  Blue with Purple (UP)
7.  Blue with Brown (UB)
8.  Blue with Black (UB)
9.  White (W)
10. White with Red
11. White with Yellow (WY)
12. White with Blue (WU)
13. White with Green (WG)
14. White with Purple (WP)
15. White with Brown (WN)
16. White with Black (WB)
17. Green (G)
18. Green with Red (GR)
19. Green with Yellow (GY)
20. Green with Blue (GU)
21. Green with White (GW)
22. Green with Purple (GP)

23. Green with Brown (GN)
24. Green with Black (GB)
25. Yellow (Y)
26. Yellow with Red (YR)
27. Yellow with Blue (YU)
28. Yellow with White (YW)
29. Yellow with Green (YG)
30. Yellow with Purple (YP)
31. Yellow with Brown (YN)
32. Yellow with Black (NB)
33. Brown (N)
34. Brown with Red (NR)
35. Brown with Yellow (NY)
36. Brown with Blue (NU)
37. Brown with White (NW)
38. Brown with Green (NG)
39. Brown with Purple (NP)
40. Brown with Black (NB)
41. Red (R)
42. Red with Yellow (RY)
43. Red with Blue (RU)
44. Red with White RW)

45. Red with Green (RG)
46. Red with Purple (RP)
47. Red with Brown (RN)
48. Red with Black (RB)
49. Purple (P)
50. Purple with Red (PR)
51. Purple with Yellow (PY)
52. Purple with Blue (PU)
53. Purple with White (PW)
54. Purple with Green (PG)
55. Purple with Brown (PN)
56. Purple with Black (PB)
57. Black (B)
58. Black with Red (BR)
59. Black with Yellow (BY)
60. Black with Blue (BU)
61. Black with White (BW)
62. Black with Green (BG)
63. Black with Purple (BP)
64. Black with Brown (BN)
65. Dark Green (DG)
66. Light Green (LG)



© RWP dec. 2004