headlight wire

Hi can i use this wire to repair my headlight wires my bulbs are 55/60 watts H4 each side has its own wiring and fuse i do not think there is a relay in the system.
Conductor Specification (mm) 3 x 14/0.30
Conductor Cross Section (mm²) 3 x 1.0
Current Rating (Amps) 8.75 AMP
Overall Diameter of Cable 7.5 mm

escort14 wrote:

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Hi can i use this wire to repair my headlight wires my bulbs are 55/60 watts H4 each side has its own wiring and fuse i do not think there is a relay in the system.
Conductor Specification (mm) 3 x 14/0.30
Conductor Cross Section (mm²) 3 x 1.0
Current Rating (Amps) 8.75 AMP
Overall Diameter of Cable 7.5 mm

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The car is a 1999 Nisan Micra

If the ~0.08V drop per meter (@55W) for both the +12V and GND paths is acceptable AND that both high & low are not both on simultaneously for too long, and one wire per light/filament from the +12V and GND source, then yes, it should be ok. (A 55W bulb is about 4.15A at 14.4V.)

I'd suggest adding relays if not fitted to reduce the voltage drop and reduce switch wear & strain.   
And to use self resetting circuit breakers rather than fuses.

Thank you oldspark for your prompt reply i will recheck the wiring diagram for any relays.

That's the12volt service for you!


Now, you said "repair" as opposed to improve.
But for comparison, I too have H4 55/60W outers (though they might be 55/100W) but also H1 100W inner hibeams. I use 12G = 1.9mmDia = 2.9mm2 area for EACH filament with the H4 common/GND being two 12G cables with one to battery- and the other to a nearby chassis GND.
The +12V feeds go almost direct to my battery mounted flink (fuselink) box via heavy duty relays (New Era twin relays).
The 12G is OFC (big deal - not) with a resistance 5.9 mOhms per meter which, based on max run of 2m @ 10A, means a +12V cable voltage drop of 0.0059R/m x 2m x 10A = 0.12mV.

That is overkill. Even allowing for the GND & relay and circuit-breaker and master fink drops, it exceeds even my normal design rule of no more than a max 0.5V drop for typical loads (as compared to an industry accepted norm of 3V else maybe 2V).
By comparison, your 14/0.30 cable with 18.1 mOhms/m has an 18.1/5.9 = 3x greater voltage drop, hence assuming a 2m +12V & 2m GND at 10A = a total 0.72V drop (ignoring connection and other resistance drops) which is still well with in the acceptable norm and probably 1V max with typical fuses etc included.
But of course your 55W bulb won't even be half that 10A current so those voltage drops will be less than half.

Hence why I reckon your cable choice is fine - even by my standards.
As I said, mine is overkill, and I designed for up to 130W high beams and even a 100/130W H4 with both filaments on (until the bulb explodes and probably takes the lens and reflector with it!!).

FYI - I have separate flinks of 60A & 100A from the battery to the relays, and the fused relays each have ATS self-resetting breakers of 10A or 15A etc. The intent is that the flinks NEVER blow except for a major wiring problem - eg, a short of the feed cable to GND.


I hope I haven't confused you - your intended wire is fine.
If you find you do not have relays then - like I suggested - they could be added.
Keep in mind that this heavy wiring is only needed for the lamp power path, not from the switches to the relays.