main beam not working

[foxface]

Hi all, I have a fault with the main beam, side lights and dipped beam working, when i switch to main beam the dipped beam turns off and main beam does not come on, it all works if i flash the main beam. Regards Terry

[foxface]

forgot to say dolomite sprint 1978

[MIG Wielder]

Hi Terry, The fact that the headlamp flasher works proves the headlights and the wiring to them is O.K. from the switch as the headlamp flasher is powered from the purple "always live" wire.
So that leaves the column switch which may have dodgy contacts or there is a headlamp main beam relay in the blue/ white wire line that has failed.
The relay switching of the headlight supplies is always a good idea if its not already been done.
HTH,
Tony.

[Carledo]

Has to be the dipswitch really, if a relay (if fitted) had failed, it wouldn't work on flash either, as while the input is different to the switch, the output wire (whether to relay or lights) is the same one on main beam or flash.

Might be a bad contact in the switch, if you're lucky a clean will fix it. If you're unlucky the switch has melted! Not an uncommon occurrence when halogen bulbed headlights have been fitted without relays. Not unheard of, even on a standard car!

But the wiring and dipswitch on a standard car is barely able to carry the load as it is, the increased load imposed by halogen bulbs is a recipe for disaster. With dipswitches being increasingly expensive, harder to source and the quality of the new ones available deteriorating daily it behooves you to futureproof it with more modern tech. If your switch HAS failed catastrophically, don't just replace it, get some relays in there first!

Steve

[cliftyhanger]

I dispute that the halogens are to blame, they only take a max of 1A per bulb extra assuming the car previously had P45T (glow worms) bulbs fitted.
The issue is the switchs are simply getting slowly burnt out. So the solution for ANY bulbs is to fit relays before the switch dies.
LEDs are probably an exception as they halve the current.

[Carledo]

I dispute that the halogens are to blame, they only take a max of 1A per bulb extra assuming the car previously had P45T (glow worms) bulbs fitted.
The issue is the switchs are simply getting slowly burnt out. So the solution for ANY bulbs is to fit relays before the switch dies.
LEDs are probably an exception as they halve the current.

Don't know how you worked THAT out. Math below. But single lamp increase is irrelevant when all 4 main beam's current draw goes through the poor overworked dipswitch and wiring at once and sometimes for long periods.

The Math, when I went to school, amps equals watts divided by volts, so, for 4 standard sealed beams, that's 4x45w or 180w, divided by 12 (volts) is 15 amps continuous load.

Now take a typical Halogen setup of 2 H4s (65w each on main beam) and 2 H3s (75w each) for a total of 280w divided by 12 is 23.3+amps or very nearly 50% more current draw than the stock setup! No wonder the dipswitch melts in protest! OK i've just looked again and in reality that's only just under 2amps per bulb, but that's STILL almost 50% extra load, which is the relevant figure!

Wouldn't be too sure about LEDs either. Whilst I'm aware that one instance doesn't make a statistical universe, on the 2018RBRR, Mahesh's Sprint lost it's dipswitch catastrophically just short of JOG about 7am and just about sunrise. We lost ALL headlights! He'd had LEDs in for about a year at that point! Fortunately I was able to wire round it to give constant dipped lights when headlights switched on and main beam on flash in case of need. Was the only failure of the 2166mile run.

Steve

[cliftyhanger]

The halogen bulbs I have used have always been rated at 55w, hence the circa 1A increase.

[MIG Wielder]

The Ohm's Law calculation is good for the running current of a hot filament bulb but it ignores the peak surge switch-on current which can be around 10 times the running current. To get an idea of the peak current , measure the cold resistance of a filament bulb ( multimeter) and use that for the calculation.
Typically a headlamp sealed beam unit will have a surge current lasting for 100mS.
Tony.

[Carledo]

The halogen bulbs I have used have always been rated at 55w, hence the circa 1A increase.

A normal H4 bulb (472) has a main beam at 65w and a dip of 55w, the same goes for the halogen version of the old 410 Tungsten bulb (can't remember the number) as used in bulb conversion square headlights for Toledos. Most conversion kits use a single filament H3 for the inner headlight on 4 lamp cars which is 75w.

Regardless of all this, the amperage required to fire a relay is miniscule in comparison (less than 1a per relay?) which SHOULD make the dipswitch and the wiring inside the car effectively immortal. I always put my relays as close as possible to the unit they are powering, so, on Dolomites, they are at the front end of the o/s inner wing.

When I rewired the Dolomega to accept the Vauxhall engine, I not only made a loom for engine and transmission management but also stripped and re-engineered the car's original loom to bring it up to modern standards of safety and efficiency. So it now has 24 fuses instead of 2 and 17 relays instead of none! A handful of relays are used on the engine and another handful on accessories like electric windows, spotlights and central locking, but all the high draw components like headlights (main and dip) HRW, starter solenoid, rad fan etc also have relays to preseve the wiring and switchgear for posterity! I'm not suggesting everyone, or even anyone, else do this, it was big faff and took me most of one winter to do it, but it was fun in a way and very satisfying when everything worked as designed when I fitted it!

Steve

[foxface]

Thanks for your replies, no relay fitted on main beam circuit, only on dipped beam. Regards Terry