Reply With QuoteGive me 20 min and I'll have a look. Was in the middle of pulling SWMBO's Ser 2 headlights apart b4 dinner. Will b back out there shortly!
Super Moderator
Can anybody identify the terminals on an H4 bulb please?
High beam
Low beam
Earth
If you don't like trucks, stop buying stuff.
YarnMaster
SubscriberGive me 20 min and I'll have a look. Was in the middle of pulling SWMBO's Ser 2 headlights apart b4 dinner. Will b back out there shortly!
1995 Mercedes 1222A 4x4
1969 (Now know! Thanks Diana!!) Ser 2 Tdi SWB
1991 VW Citi Golf Cti (soon to be Tdi)
'When there's smoke, there's plenty of poke!!'
'The more the smoke, the more the poke!!'
ForumSage
(A) LH lug = Common.
(b) Top lug = Low beam
(C) RH lug = High beam.
when looking at the back of the globe, or your drawing.
Common is not 'earthed' through the metalwork.
Super Moderator
I keep loosing a low beam, high works fine so I must have a dicky connection on T-B, every time I touch the back of the fitting the light comes back to life.
If you don't like trucks, stop buying stuff.
ChatterBox
Can you elaborate? I was working on mine a few weeks ago, and noticed the black wires earthed to the body.Originally Posted by superquag
At any given point in time, somewhere in the world someone is working on a Land-Rover.
ForumSage
"...Can you elaborate? ..."
Yes.... can I ever elaborate !!!!!!
O-Kaaaaaaaayy...here goes:
In a H4 bulb you've got two filaments. Hi and Lo beam.
One end of each is connected to (and each other, obviously) the same pin, in this case the 'common'
The other end of each filament is brought out to it's own designated pin.
The pin called 'common', or sometimes 'earth' is NOT connected to the metal housing and base of the bulb, which is why it is'nt a great idea to call this pin 'earth'.... My mistake in not making that clearer.
This arrangement gives car manufacturers a choice. This is not a Good Thing, 'cos they'll all do it dIfFeRAntLY, even between models.
You can have the common going straight to 'earth' or the body, and feed power down the lines from your beam-switch.
This means a power wire UP to the beam switch...and TWO power wires to feed the H4 bulb. This is the most logical way.
But, a silly way is to feed power to.... the Common. Then, the two wires go to the headlights/beam switch which simply 'earths' the one which needs to be lit up.
This saves ONE piece of wire....
Notice we have'nt used POSITIVE or NEGATIVE, as the same principal applies to Pos. earth systems as well as the (99.9%) standard, Neg. earth.
Enough info ?
ChatterBox
At any given point in time, somewhere in the world someone is working on a Land-Rover.
ChatterBox
No, seriously, that IS very helpful. And I understood it all, too!
At any given point in time, somewhere in the world someone is working on a Land-Rover.
ForumSage
Bugger! - I'll try harder next time....
ForumSage
Which is eaxactly why you get some very funny results when wiring up a set of spotlights to say, a Prado, if you use the traditional method of taking a feed from the "high beam" terminal on your H4 globe to "switch" your relay."...Can you elaborate? ..."
Yes.... can I ever elaborate !!!!!!
O-Kaaaaaaaayy...here goes:
In a H4 bulb you've got two filaments. Hi and Lo beam.
One end of each is connected to (and each other, obviously) the same pin, in this case the 'common'
The other end of each filament is brought out to it's own designated pin.
The pin called 'common', or sometimes 'earth' is NOT connected to the metal housing and base of the bulb, which is why it is'nt a great idea to call this pin 'earth'.... My mistake in not making that clearer.
This arrangement gives car manufacturers a choice. This is not a Good Thing, 'cos they'll all do it dIfFeRAntLY, even between models.
You can have the common going straight to 'earth' or the body, and feed power down the lines from your beam-switch.
This means a power wire UP to the beam switch...and TWO power wires to feed the H4 bulb. This is the most logical way.
But, a silly way is to feed power to.... the Common. Then, the two wires go to the headlights/beam switch which simply 'earths' the one which needs to be lit up.
This saves ONE piece of wire....
Notice we have'nt used POSITIVE or NEGATIVE, as the same principal applies to Pos. earth systems as well as the (99.9%) standard, Neg. earth.
Enough info ?
I learnt this the hard way when I first wired up some lights on one of my work Prado's.
Cheers .........
BMKAL
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