phatbenny
New member
Sounds like relays is the way to go then. Was hoping to avoid this because I'm a bit of a beginner, but I guess I need to jump in at the deep end then.
General headlight bulbs
- Thread starter d miller
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General headlight bulbs
phatbenny
New member
OK here's the inevitable question. I've done a bit of reading, what do I need SPNO (Single Pole Normally Open) or SPCO (Single Pole Change Over)? 
I told you I was an amateur when it comes to electronics (.. and cars). I'm going to take a guess at it and say I need SPNO. As in the switch is normally open and therefore off. A bit of power through it and it closes the swicth.
I told you I was an amateur when it comes to electronics (.. and cars). I'm going to take a guess at it and say I need SPNO. As in the switch is normally open and therefore off. A bit of power through it and it closes the swicth.
i have had halfords 50% extra power headlight bulbs in my panda for almost a year, and i have had no trouble, the bulbs i had were the old fashioned round ones, but the new ones are H4 55W bulbs (not sure if they are going to pass the mot though).
John H
Established member
phatbenny said:
Yes.
A pair of these from Maplins should have no trouble with the 10+ amps running current, or the power on surge.
N02AW 40A SPNO Auto 12Vdc 781 in Stock £1.99
One for both dip, the other for both mains.
phatbenny
New member
Ok, so I've got my relays, inline waterproof fuse holders, fuses and 17amp wires.
I've put one length of 17amp wire onto the positive connector on the alternator, and put a 15amp fuse onto it which should be enough for two 60w bulbs. Now my plan is to split down to two seperate wires which go to two seperate relays. One for dipped and one for fullbeam. After each relay output I will have two wires coming out, one for each side of the car. Now my problem is I don't know anything about the bulbs. They are H4 bulbs with three spades connectors coming out of the end. Now, I don't know which one of the three spades is for what. I've tried the multimeter but at the end of the day I can't get my head round the whole negative positive thing, especially not at this time of night.
So, can anyone enlighten me. What goes into each of the three prongs?
Now I'm guessing that the prong at the top is for negative/earth.
So the other two prongs are both positive? With different voltages going to them, one for dipped one for fullbeam. Now if this is the case, what gives the one prong a lesser voltage? And if this is the case then surely putting in 12v relays will just cancel out the lesser effect of dipped beams?
Now I'm hoping that somebody is going to say, "Don't be daft ben, you need a 12v feed to each of the two prongs, the bulb does all the clever step down stuff all by itself." Which brings me back to my origional question, which prong is which.
Anyone who can read and make sense of what I've just written is my hero, even more so if they can answer all the questions hidden in there?
p.s. If I find any of the answers myself, I'll let you know.
I've put one length of 17amp wire onto the positive connector on the alternator, and put a 15amp fuse onto it which should be enough for two 60w bulbs. Now my plan is to split down to two seperate wires which go to two seperate relays. One for dipped and one for fullbeam. After each relay output I will have two wires coming out, one for each side of the car. Now my problem is I don't know anything about the bulbs. They are H4 bulbs with three spades connectors coming out of the end. Now, I don't know which one of the three spades is for what. I've tried the multimeter but at the end of the day I can't get my head round the whole negative positive thing, especially not at this time of night.
So, can anyone enlighten me. What goes into each of the three prongs?
Now I'm guessing that the prong at the top is for negative/earth.
So the other two prongs are both positive? With different voltages going to them, one for dipped one for fullbeam. Now if this is the case, what gives the one prong a lesser voltage? And if this is the case then surely putting in 12v relays will just cancel out the lesser effect of dipped beams?
Now I'm hoping that somebody is going to say, "Don't be daft ben, you need a 12v feed to each of the two prongs, the bulb does all the clever step down stuff all by itself." Which brings me back to my origional question, which prong is which.
Anyone who can read and make sense of what I've just written is my hero, even more so if they can answer all the questions hidden in there?
p.s. If I find any of the answers myself, I'll let you know.
phatbenny
New member
I've found out a bit more.
The terminal deisgnations for the bulb are 56a(High beam), 56b(Low beam), and 31(Ground).
So now I'm still trying to work out if 56a and 56b both need a 12v feed. The Daniel Stern article suggests this is the case.
Now I need to try and find out which is which on the bulb. See what I can find.
The terminal deisgnations for the bulb are 56a(High beam), 56b(Low beam), and 31(Ground).
So now I'm still trying to work out if 56a and 56b both need a 12v feed. The Daniel Stern article suggests this is the case.
Now I need to try and find out which is which on the bulb. See what I can find.
phatbenny
New member
The internet has failed me. I can't find any graphical information about H4 bulbs terminal designations. I did find a few other things.
So, an H4 bulb is a dual fillament bulb. I don't know if the fillaments are the same size, or if they both light up at the same time for full beam.
Either way all my reading suggests that both the full beam and normal beam terminals need a 12v feed.
Tomorrow I'm going to find someone to teach me how to use a multimeter properly, and maybe a bit about circuits. Then I'll come home and find out what I need to know from the car. Then I'll share it with you.
So, an H4 bulb is a dual fillament bulb. I don't know if the fillaments are the same size, or if they both light up at the same time for full beam.
Either way all my reading suggests that both the full beam and normal beam terminals need a 12v feed.
Tomorrow I'm going to find someone to teach me how to use a multimeter properly, and maybe a bit about circuits. Then I'll come home and find out what I need to know from the car. Then I'll share it with you.
John H
Established member
As you've found out, the lamp has two filaments with a common earth.
Three connectors in total.
One filament is for dip (and has a little piece of metal inside the envelope next to it to mask the beam to give the cut off you expect on dip).
The other filament is main beam and is clearly visible.
In normal operation you have one beam or the other running full power.
The only exception to this is "dimmed dip" when the lights are switched to the first position when driving.
Depending on how you've wired it, and the sensitivity of the relay, you may find that you no longer have "dimmed dip", but full power dipped beam on the first switch position.
I'll post later which connector is which, as I don't know off the top of my head.
P.S. You know about not touching the "glass" of the bulbs with your fingers?
"Touching the Glass: the glass envelope of a halogen lamp should NOT be touched with bare hands because the oil from human hands may cause the lamp to fail prematurely. If you should touch the glass envelope by accident, wipe it clean with alcohol."
Three connectors in total.
One filament is for dip (and has a little piece of metal inside the envelope next to it to mask the beam to give the cut off you expect on dip).
The other filament is main beam and is clearly visible.
In normal operation you have one beam or the other running full power.
The only exception to this is "dimmed dip" when the lights are switched to the first position when driving.
Depending on how you've wired it, and the sensitivity of the relay, you may find that you no longer have "dimmed dip", but full power dipped beam on the first switch position.
I'll post later which connector is which, as I don't know off the top of my head.
P.S. You know about not touching the "glass" of the bulbs with your fingers?
"Touching the Glass: the glass envelope of a halogen lamp should NOT be touched with bare hands because the oil from human hands may cause the lamp to fail prematurely. If you should touch the glass envelope by accident, wipe it clean with alcohol."
phatbenny
New member
Cheers John,
yep I know about not touching the glass. I don't knock the glass either. Kills fishes.
Amazing. Thanks for the info. I should be able to work out which terminal is which now. So that means that only one fillament is in use at any one time. Therefore I can:
Bring a single 17amp wire from the alternator,
put a 15amp fuse on it,
split it to a wire for a high beam relay and a wire normal beam relay,
and after the relays split the 12v output further to the two seperate lights,
all without melting my circuit. ?
yep I know about not touching the glass. I don't knock the glass either. Kills fishes.
Amazing. Thanks for the info. I should be able to work out which terminal is which now. So that means that only one fillament is in use at any one time. Therefore I can:
Bring a single 17amp wire from the alternator,
put a 15amp fuse on it,
split it to a wire for a high beam relay and a wire normal beam relay,
and after the relays split the 12v output further to the two seperate lights,
all without melting my circuit. ?
John H
Established member
phatbenny said:
Sorry, no.
On the plug you removed from the bulb, the black wire is the earth connection, which is the lefthand prong looking towards the back of the bulb.
The top one is grey, or grey/black for the passenger side, and is +12 volts here for dip beam only.
Leaving the righthand (green or green/black) which is +12 volts here for main beam only.
Regarding melting things, if the relays are wired in correctly, so that the wires which used to feed one of the bulbs actuate the the relays, and the high current for the 60Watt bulbs is all provided by your new wiring and the contacts of the relays, there shouldn't be any grief.
The relays only take a fraction of an amp to operate, and the old switches and wiring are rated for about 8 amps
Last edited:
phatbenny
New member
Once again, John H, where would I be without you. Amazing source of info.
Tonight I managed to stick a relay and 12v supply on the dipped beam, and the results are awesome. No longer is night time panda driving an extreme sport. Tomorrow I'll finish up by doing the full beam, and probably adding a set of spot lights to the front bumper.
Tonight I managed to stick a relay and 12v supply on the dipped beam, and the results are awesome. No longer is night time panda driving an extreme sport. Tomorrow I'll finish up by doing the full beam, and probably adding a set of spot lights to the front bumper.
phatbenny
New member
Finally finished the job, just thought I'd show you the results. I'm quite please, no fear of night driving now.
Normal beam
Full beam
Full + Rally Lights
Normal beam
Full beam
Full + Rally Lights
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