The original “torpedo” shaped Lucas fuse type was applied in the two fuse blocks of the XK 140 . This story deals with the difference between original Lucas type fuse with conical ends and the later type with straight ends.

In addition it makes an inventory of the actual maximum power consumption per circuit and the Jaguar prescribed fuse rating, which is not always consistent. Furthermore, with the arrival of the XK 150, Jaguar corrected a number of fuse ratings although the maximum power consumption of most of the circuits did not change.

Original Lucas type fuses

Lucas type fuses are used throughout the 40’s, 50’s and 60’s in British automobiles. The physical length of the Lucas type of fuse was originally 1¼ inch with conical ends and  changed to 1 inch for the later fuse types with straight ends. The change-over from conical to straight ends took place towards the end of the 50’s. The former conical fuses kept their Lucas part number although they now had straight ends. Additional fuse ratings were introduced, receiving new part numbers (188 230 and higher).

The above introduction implies that all XK’s had the original type of Lucas fuses with conical ends installed when they left the factory.

Fuse ratings

Lucas fuses have three ratings:

• continuous current they are designed to carry
• instantaneous current at which they will fuse
• continuous current at which they will also fuse.

The figure found on Lucas fuses is the continuous fusing current which is twice the continuous ampere rating that the system should be using; this can be a source of confusion when replacing Lucas fuses with non-Lucas fuses. Lucas type fuses use a specific colour code for each rated current (see table below using the description of the fuse when the part number was introduced).

Color coding scheme 1958

Color	Lucas code	Type end	Cont. Amp	Instant. Amp	Cont. Amp (50%)
Red on Yellow	188 206	Conical	5	6	2.5
Green on Black	188 211	Conical	10	12	5
Light Brown	188 220	Conical	15	18	7.5
Pink	188 216	Conical	25	30	12.5
White	188 218	Conical	35	40	17.5
Purple on Yellow	188 219	Conical	50	60	25
Yellow on Red	188 222	Conical	60	75	30
Yellow	188 230	Straight	4.5	5	2.25
Green	188 232	Straight	6	7	3
Nut Brown	188 234	Straight	8	10	4
Red on Green	188 235	Straight	10	12	5
Red on Brown	188 236	Straight	12	14	6

Early type Lucas 188.216 with conical ends and 1¼“ length

Later type Lucas with straight end and 1” length

Lucas original Green boxes for conical 1¼ “ fuses 188 216

Later Red boxes for 1” straight end 188 219 fuses of 50A

Later Lucas 188 219 fuses of 50A (about 1962)

Jaguar prescribed fuse ratings for the XK 140 SE

The table below gives an overview of the maximum load per fused circuit and the Jaguar prescribed fuse rating.

Below you’ll find the circuit division for the XK 150. Please notice that for XK 140’s  the circuit with Interior Lights and Cigar Lighter was fused with a 35 Amp fuse placed at the 4th position of SF 4. For XK 150’s this circuit moved to position A2 of SF6 with a 50 Amp rating. Position 4 of the SF4 fuse block of the XK 150 was now used for fusing the Fog Lamps, which had no fuse at all on the XK 140 (although position A2 of SF6 was available). Also notice that the fuse for the  Head Lamps circuit increased from 35W to 50W with the introduction of the XK 150. Even more remarkable: position number 2 of SF4 (side lamps, tail lamps, boot lamp and number plate lamp)  increased from 15 Amps to 50 Amps!