Hah - my replacement bulbs have just arrived... and I've managed to order some 100W ones in error
I might be making some leads very similar to blacktiger's !

Parts for wiring bought... plus a pair of :
Ring TWIN PACK 12V 60W HB3 ULTRA XENON +50% Headlight Bulb RW9905

I'll post results as and when.

phil_h wrote:

Just had both bulbs blow in my new-to-me 13 reg hse, and there's lots to read !
So, as I'm a retired electronics engineer, I thought I'd better pitch in with my 2-pennorth

The service bulletin with fitting instructions was very interesting as it shows the resistive cable being clipped below the lamp with no concern for anything being hot... so that means that there is very little resistance involved !

Note to blacktiger - 10 ohms is a far greater resistance than the bulb so I think you got your decimal point in the wrong place

Now, if LR thought the lights would still be acceptable with the resistance in series, then it will only be like losing less than a volt.
The heat in the bulb is proportional to the power consumed, which is V^2 / R so to reduce the bulb temperature it wont need much voltage reduction.
If we assume 60W and 13V then R(bulb) = 2R8 (2.8 ohms) approx. and I = 4.65A approx.

For 0.5V lost across a resistor in series with the bulb, 0.5V / 4.65A = 0R1 approx (0.1 ohms blacktiger !)
The bulb would then be seeing about 12.5V, and hence consuming about 12.5^2 / 2.8 = 55.8W approx. - a 7%ish power reduction.
And the 0R1 resistance would consume 0.5^2 / 0.1 = 2.5W
That would get hot if its a resistor, so a 10W rated metal-body resistor would be the smallest I would consider, and a 25W rated one would be best, even if it is bigger.
If 2.5W was spread along both wires in a 30cm cable, then it may be fine... but it will probably need heat resistant sheathing ... which may be why they stopped issuing them???

The current when someone fits a 100W bulb to overcome the loss in light will make the series resistance consume 60% more power too! ie that 2.5W will go up to 4W which a 25W metal-clad power resistor will handle fine, but anything else will get very much hotter.

Yep that's what I said!.

Seriously though thank you for the detailed and knowledgeable response  Landrover - turning owners into mechanics since 1948

2014 Orkney grey Freelander SD4 GS.
2004 Zambezi silver Discovery 2 Td5 (Gone)
1963 Surf blue Morris Mini Minor Super de Luxe (my little toy)

Quote:

Yep that's what I said!.

But I said it better :raspberry:

Bobupndown wrote:

Landrover - turning owners into mechanics since 1948

just spotted this... wish I'd known that before we bought it

You could just give up on the JLR type HB3 mod and fit a HID kit

Click image to enlarge

But they're illegal and will fail the MOT. MY13 Santorini Black SD4 HSE

Hmm... maybe less of a problem than a perfectly standard setup's standard defects

Repair immediately (major defects):
Central Stop lamp(s) not working (4.3.1 (a) (ii))
Nearside Headlamp not working on dipped beam (4.1.1 (a) (ii))
Nearside Headlamp not working on main beam (4.1.1 (a) (ii))

blacktiger wrote:

But they're illegal and will fail the MOT.