Headlight wiring diode getting very hot. Help needed

[shayne]

Working my way through my project and I'm at the stage where I'm trimming all my wires to length and crimping terminals on etc.

This is a full rewire using aftermarket lights and switches.

My headlight has 3 wires, ground, low beam and high beam. When lights are off and I hit the flasher button it's bringing on my tail light, the tail light and low beam are fed off the same 12v.

12v from the main beam is going back up the low beam wire and switching my tail light on. So I installed a diode on my low beam wire so current can only go one way and it's worked but on testing it with the low beam on as if riding at night, within 30seconds the diode gets bloody hot and I'm worried it may melt through the heat shrink and cause issues.

Any one used diodes before, is this heat normal? Can I get a bigger diode to stay cooler or can I wire it differently? Will confirm what diode I've used later but according to Google and multiple Internet forum sources the diode I bought was upto the job.

Not overly confident with electrical speak, Google got me this far, this is one of 3 wiring gremlins that I have to sort so looking for advice.

 

[mydlyfkryzis]

Is this on a motorcycle? A make, model and year would allow for better help.

You probably have a bad ground or mis-wired the signals. Since we don;t know if the bike is stock wiring or not, it is hard to even guess.

Some bikes have front running lights and signals (dual element bulb) and some have single element turn only. Without knowing the bike and what mods, it is difficult to point you in the right direction.

A diode should not be needed...if wired correctly.

 

[shayne]

Sorry I didn't mention Make and year as nothing from that bike has been used apart from alternator, rectifier, and igniter. But it's a 1979 Kawasaki z650

I'm using a Chinese eBay headlamp with a dual filament head light bulb

Wiring is an ultima small all in one job.

When plumbing this in, I found the ultima powered my tail light all the time so I didn't use that supply and just tapped my tail light on to my low beam feed so my tail light comes on with my headlight.

I have 12v supply to my handle bar switch
Low beam 12v out of switch to ultima box then back to headlight
High beam 12v out of switch to ultima box then back to headlight
I have a momentary switch that I've connected to the incoming 12v supply and to the high beam wire.

I have also wired the headlight without going through the ultima box and it still brings on my tail light when I flash my high beam.

 

[mydlyfkryzis]

You may have the headlight wired wrong....or you have a bad ground. There are 3 connectors for the headlight.

The green is common, white low beam, blue high beam , on my schematic.

So if you have a 3 prong connector, looking from the back, the ground is on the right. If you swap the connectors by mistake, High
beam supplies power to the ground, sending power through the high beam element (to ground) and becuase of the resistance, will also send power through the low beam. So if you hooked High beam to the wrong pin, when you power high beam, the low beam is powered and will also power everything on the low beam circuit.


If you have the low and high beam on the correct pins, then a bad or weak ground will cause the powered beam to ground itself through the other circuit, giving the same effect, power to the high beam, circuit will cause a back feed of power through the low beam.

So:
1. Make sure the ground is good.
2. Make sure the low is on low pin and High is on the high pin.

 

[Sonreir]

+1 to what Richard is saying. A diode shouldn't be needed. Most diodes can't handle the kind of current being pulled by the headlight, so that's why it's getting so hot.

 

[shayne]

The headlight came with no plug just wires.

Red yellow and blue. I'll try a diff wire config tonight and see. Let's hope this works as I don't fancy running the diode.

 

[shayne]

All sorted lads, BIG THANK YOU.

I had wired it up wrong.

Diode in the bin. Wires swapped around and all as normal.

When I first wired the lamp up I thought as I got the bulb to light up dimly and flash that the wiring sequence I had was correct. Oh no. Lesson learnt.

Cheers guys saved me some stress.