Headlight relays

[Biker9090]

It's getting darker now and I forgot how appalling my CBF500 headlight is.

I'd rather avoid the PITA of trying to find an entirely different unit and cram the harness in - LED conversions also concern me re MOT failure.

I've read about fitting relays to the headlight circuit to improve it.

Has anyone done this on another bike and had success?

[KTMsm]

It would have to be pretty poor design that a relay would make an appreciable difference

I'd just get a better bulb or brighter (illegal) bulb, extra lights or go for the LED option but as you say I'd keep the old bulb for the MOT

Although many of the modern / better LED are fine with a clean cut off

[bogie]

As above, get the bulb, you can always change it out each year for MOT. Or look at a new LED headlight. I bought one for my Harley for £100 ish off amazon about 6 years ago and its fantastic, same 5 3/4" size/style as OE, just multiple LEDs. So long as you setup the aim correctly will go through MOT just fine.

[gareth_r]

An LED headlamp bulb is not, in itself, an MOT failure.

https://www.gov.uk/government/collections/mot-manu...

You can buy LED bulbs from the likes of Osram and Philips.

Edited by gareth_r on Thursday 19th September 22:18

[OutInTheShed]

You could measure the voltage drop from battery to bulb, on both switch and return paths.
That would tell you what gain is to be had from a relay.

You could also check the generator/rectifier/regulator is giving a good voltage.

Back in the days when bikes had 7 inch round headlights, someone did me a favour by putting a stone through mine, causing me to buy a cibie, which was very much better than the OE with its slightly tarnished reflector and poor design.

These days, if I rode much at night, I'd get some LED auxiliary lights I think.

[black-k1]

If you are getting enough of a voltage drop to the headlight that a relay will make a noticeable difference then finding out why you have the voltage drop is the priority.

To improve lighting you have 6 options:

Fit a brighter halogen bulb of the same wattage. - Straight swap and easy. No MoT issues. No realignment check required. Will likely make a small difference.

Fit a halogen bulb with a higher wattage. Straight swap for the bulb but check the wiring can handle the addition amps. May also need a relay. Technically an MoT fail but no tester is going to check the wattage of the bulb. will make a more noticeable difference.

Fit an LED "bulb". May have issues fitting into headlight unit but wiring is easy. May need headlight alignment adjusted. No MoT issues if alignment is correct. Likely to make a noticeable difference though it's possible to buy poor LED headlight "bulbs"..

Fit an HID "bulb". Will need to find a location for the ballast but wiring is easy. May need headlight alignment adjusted. No MoT issues if alignment is correct. Likely to make a significant difference.

Fit a replacement headlight unit. Expensive for a good one and will need fitting and realignment. No MoT issues if alignment is correct. Likely to make a noticeable difference though it's possible to buy poor LED headlight replacement units..

Fit additional/auxilary lights.Expensive for a good ones and will need fitting with relay and switch then alignment. No MoT issues if alignment and switching is correct. Likely to make a noticeable difference though it's possible to buy poor auxiliary..

[steveo3002]

fitting a relay to older vw's transforms the headlights

use a multimeter to see what the voltage is at the bulb with the engine on

[Fastdruid]

Biker9090 said:

It's getting darker now and I forgot how appalling my CBF500 headlight is.

I'd rather avoid the PITA of trying to find an entirely different unit and cram the harness in - LED conversions also concern me re MOT failure.

I've read about fitting relays to the headlight circuit to improve it.

Has anyone done this on another bike and had success?

First off. This is the bulb I fitted to my VFR750F. https://www.ebay.co.uk/itm/383193816047 (technically I know it's a car "kit" with two bulbs but I couldn't find a single one of that exact type).

It's literally just passed an MOT with it fitted and the tester commented on how good the headlight was.

Secondly, relays. Yes. RVF400R. For slightly different reasons, mostly because they have a habit of melting the (increasingly rare) hi/lo switch if you fit 60/55 rather than the OEM (and hideously expensive) 60/35 originals. Fitting a relay means you're no longer putting a load of amps through the switchgear and it lasts much longer.

Anyway, fitted a second relay (hi beam was already on a relay) along with another "power" relay for it (ie so *no* significant power was running through the ign switch) and upgrading the wires to both the relay(s). It resulted in a noticeable improvement.

[Biker9090]

Thanks.

Yeah, I'm going by the German market CB500R which apparantly does have two relays fitted and is allegedly better (engine and charging system is identical).

Albeit, I have fitted a much larger stator and reg/rec so the charging system on mine is VERY strong.

I've finally found my multimeter so will have a look and see what the drop is.

Hmmm, maybe do some more research on the other bulb options then. I would fit better spot lights but there isn't anywhere they can really fit on this - you can add engine bars but to do so requires removing the front engine bolt which after 80,000 miles is likely welded stuck....

[Krikkit]

Fastdruid said:

Secondly, relays. Yes. RVF400R. For slightly different reasons, mostly because they have a habit of melting the (increasingly rare) hi/lo switch if you fit 60/55 rather than the OEM (and hideously expensive) 60/35 originals. Fitting a relay means you're no longer putting a load of amps through the switchgear and it lasts much longer.

For this reason alone I'd fit relays to an older bike.

[Jazoli]

Biker9090 said:

Thanks.

Yeah, I'm going by the German market CB500R which apparantly does have two relays fitted and is allegedly better (engine and charging system is identical).

Albeit, I have fitted a much larger stator and reg/rec so the charging system on mine is VERY strong.

I've finally found my multimeter so will have a look and see what the drop is.

Hmmm, maybe do some more research on the other bulb options then. I would fit better spot lights but there isn't anywhere they can really fit on this - you can add engine bars but to do so requires removing the front engine bolt which after 80,000 miles is likely welded stuck....

Just stick a decent quality LED bulb in it and forgot about it.

[OldGermanHeaps]

The way to check if a relay harness , or wiring repairs would help is, digital multimeter set to vdc, in a range suitable for 12v.
Put red probe backprobed onto headlight dipped + terminal with the bulb in circuit. Put black probe on battery +, with headlights on you should see less than around half a volt. Any more and there is resistance somewhere and a relay harness would help.
Repeat for full beam.

Then backprobe red lead to headlight bulb - terminal and black lead to battery -
Should be less than 0.2 to 0.3v, if more you have a bad earth somewhere.

If your bike passes the above tests a relay harness wont make a bit of difference.

But good quality led bulbs or even better full led headlight assemblies are st hot now. They last ages, brighter, more consistent, their voltage regulators and reduced current draw overcome a lot of wiring shortcomings, and they put less strain on your battery and reg/rec

I would try something like this 7" LED Motorcycle Headlight Assembly With DRL Turn Signal Lights For Honda CB400 CB500 CB1300 Hornet 250 600 900 VTEC VTR250 H4 https://amzn.eu/d/3QYYos2

From amazon so its easy enough to return if you dont like it, but i suspect you will be impressed by the difference.

Edited by OldGermanHeaps on Sunday 22 September 22:57