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Headlight volts drop - Printable Version

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+--- Thread: Headlight volts drop (/showthread.php?tid=80145)

Headlight volts drop - Mustang - 09-10-18

i notice when I switch my lights on sometimes the clocks go off then come back on, also if I pull the pass light switch in. I did a test with the lights disconnected and that stopped the clocks going out. I’ve checked the battery voltage and it drops quite a bit when the lights go on, I guess it’s enough to cut the clocks out. Has anyone altered their lights to fire them off a relay? Would it make any difference? Gen 1 2001

Re: Headlight volts drop - Fazerider - 10-10-18


The resistance of a cold tungsten filament is very low so the initial current is huge, easily enough to cause the loss of some volts along the wiring and particularly across any connectors that aren’t as tight or clean as they should be. Always worth a check to see if any connectors are showing signs of getting hot.
Don’t forget to check the path on the “cold” side of the lights/instrument panel too, if the earthing is bad the effect is the same… fewer volts where you need them.
If the wiring and connectors are in decent condition and you still have the problem then you can run in a second wire (fused!) to supply the lights via relays switched by the existing wiring.
When you say you measured the battery voltage, was that directly across the battery terminals? If there is a significant drop there then a new battery may help, though normally the first sign of a dying one is the starter motor struggling to spin the engine.

Re: Headlight volts drop - Mustang - 10-10-18

Thanks mate, I’ll carry out a Few checks, the bike already has relays I’ve discovered same as the r1.

Re: Headlight volts drop - b1k3rdude - 12-10-18

If its a gen 1, these are notorious for
  1. having undersized cables in the sub-loom, sits under the front cowling, connects to the main loom.
  2. the same undersizing on the cables going from the reg-rec to the main loom.
My FZS had a similar issue in that the volts at the clocks was sitting around 10v with the headlight on, I go around this issue by running an extra ground to the clock from the small frame mount above the reg-rec. Then I changed the halogens for LED - I went for a fanless design because rain would just kill a little fan in now time, and where the shaft behind the bulb is the exact same width and length so the rubber headlight boots seal against them keeping the headlight sealed.

These LED bulbs have several benefits over HID but primarily you get proper hi beam and with a much better low beam pattern.


Re: Headlight volts drop - Mustang - 12-10-18

(12-10-18, 08:31 AM)b1k3rdude link Wrote: If its a gen 1, these are notorious for
  • having undersized cables in the sub-loom, sits under the front cowling, connects to the main loom.
  • the same undersizing on the cables going from the reg-rec to the main loom.
My FZS had a similar issue in that the volts at the clocks was sitting around 10v with the headlight on, I go around this issue by running an extra ground to the clock from the small frame mount above the reg-rec. Then I changed the halogens for LED - I went for a fanless design because rain would just kill a little fan in now time, and where the shaft behind the bulb is the exact same width and length so the rubber headlight boots seal against them keeping the headlight sealed.

These LED bulbs have several benefits over HID but primarily you get proper hi beam and with a much better low beam pattern.
Thanks for your reply, I suppose it’s just easier to fit the leds

Re: Headlight volts drop - Andy W - 13-10-18

Hope that solves your problem....great link to some tried & tested LED bulbs - they've been on my wish list for a while now!