Odd dipped beam behaviour

Hi All,
Not been out and about in the MG lately. Went out in it to give it little run that required lights on.
So, ignition on and engine running while put the seatbelt on, I switched straight to dipped beam but only the weedy sides came on. Switched off and on again, straight to dipped and they were on. Thinking about it I kinda remember it might have done this before earlier in the year when the days were longer. I seem to remember thinking headlights aren’t upto much but it wasn’t very dark. Is there something I should know?
Cheers,
Michael.

Yes, there’s something wrong.

Sorry I couldn’t resist it, I’m a bit of simpleton.
The switching is done in the stalks & they are a throw back to a Honda pattern, there have been millions of these made. But like many mechanical switches they can oxidise when not used regularly, the action of using the switch wipes the contacts & all is well, infrequent use equals potential problems.
Without getting too technical oxide buildup creates a resistance which causes a voltage drop & localised heating & that burns the contact which creates more of a resistance = more heat. All the time your lights are becoming less efficient.
Running at full capacity the electrical system is enjoying a full 13.8volt feast, stick a few ohms in series with a current hungry device & you’ve lost a whole slice of grunt; your 13.8volts required for full illumination is now 11volts & the first you know that there’s a cow in the middle of pitch dark road is when you drive up it’s arse.
There was a fad a few years ago when Freelander or possibly Discovery indicator/light switch stalks were fitted to our cars & for the older cars this made sense as they were potentially younger, I also think they are more robust both mechanically & electrically.
I have them fitted for the above reason but also because I’d designed a variable wipe compatible with those stalks & as with many of my designs the long suffering f acts as a test bed.
Other experiments around headlights & remaining within the law were high quality relays adjacent to the lamp housing with direct heavy duty cables to them, the coils being switched by the column mounted stalks & latterly power mosfet switching; this is ongoing & probably no great advance over the relay.
Use your switches fairly regularly just to give them an airing, better a few clicks before turning the ignition off than a close inspection of a cows colon.
M

Thanks Mike for that.
I’ll try to give the switch a good exercising before I use it, especially at this time of year. Hopefully It’s not too bad and there’s still plenty of contact surface remaining. If it gets too bad I’ll do what you’ve done with relays, although MOSFETS would probably be cheaper. Might rope in the Arduino for that too. Interesting that you use your F as a test bed; I might be using the Freelander for the ambient temperature widget. Although that needs work - just done the track rod ends after being an MOT advisory and the fuel tank cradle or rather the bars are going to need attention soon as one has almost rotted through.
Cheers Michael.

I was recipient of a number of the tf style relays & they’ve found their way into all sorts of things, the only minor irritation is that the two coil blades & one of the switch contacts are 4.8mm which aren’t as easy to find as the 6.3. The last relay I wrecked in the interest of science had silver flashed contacts.
The mosfet modules I’ve been using are useful enough for me to have order another batch, for more current I simply piggyback a couple. The commoned positive / switched negative takes a while to fix in the memory (70+ problem) as negative ground is so entrenched.
M

What is the advantage of using MOSFETs over relays and is there any downside with them ?

It has been good practice to switch the positive in a circuit although it doesn’t matter whether you switch the positive or the negative, which ever way up you are simply stopping current flowing.
That practice is based on safety. Different traditions describe positive & negative differently, hot/cold, send/return, supply feed, earth ground, etc, if you were dealing with high voltage DC equipment, let us use a valve guitar amp as an example & you isolate the high voltage feed (& we ignore the electrolytic smoothing caps) you could, if you were so inclined poke about with your finger even if you were stood bear footed on an earth plate. If you switch the return (negative) & you did this you would know about it in no uncertain terms, although the equipment would provide a perfect performance to accompany you being electrocuted.
So this is why it’s good practice to switch the live.
Our cars are negative earth & if you didn’t know that maybe you might consider a different discipline That wasn’t always the case, my first car radio was switchable positive earth to negative. Manufacturer changed because having a positive chassis promoted rusting (made no bloody difference in my cars!).
If you look at a circuit of cars with fairly primitive electrics (early Land Rovers) simple positive switching encompassed everything. Move on a few years & electronics starts to weasel it way in & low current electronics is no use for switching current hungry devices like head lights. So the low current circuitry was used to switch relays which switched headlights etc.
Relays are brilliant but expensive & technology has provided us with a device which takes very little driving & can switch the high currents met in car circuitry, they are also fast at switching in comparison to a relay.
And they are cheap. Or at least those that switch the negative are.
Without going into too greater detail there are two types of mosfet P channel & N channel, the N channel is more robust, remaining cool whilst switching higher currents. Obviously they are more of a problem for the lay user, as the electrics you are used to doesn’t switch the negative; the brown/red wire comes along, you cut it & insert a switch, you can now control the load. To use the mosfet your brown/red goes to the load & the return goes through the mosfet to the negative. In this way the electronics can control all your power circuits swiftly safely & silently.
I use simple two mosfet boards from china (where else) I buy them in batches of ten & those ten would cost me less than paying a standard relay & if I need to switch more current than one board can handle, I simply parallel them up & this is the basis of electric car control.
This has had to be simplified, not because you are dumb, I doubt I will have lost anyone along the trail, it’s a rambling journey if you want to touch all bases & as the song goes; if you want any more you can sing it yourself.
M

..i get it about touching all basses but what about the collectors and emitters ?

I think I will install try mosfet switching on the MGB as it has frighteningly rudimentary electrics, few relays and most loads running direct through the dash switches.
You mentioned having to run 2x or more mosfet pcbs in parallel to cooe with higher current handling. What is the rating on the type you usually buy and what is the best source to order some please ?

Just as you fix negative switching in your head why not.
The devices I use are rated at 15a & as I say I buy them in tens for £8-90ish, all in one board & i break them off as required. The picture shows two piggyback boards into a three phase bridge, the bridge is used as a switch, directing current from two medium current supplies at different potentials into one load. It acts as a fail safe as I don’t want the higher voltage feeding the lower & not the load. That would be a big pair of tits up.
M look

I would buy a couple to experiment with first & load them up to their maximum expected degree to assess whether you need to parallel boards.
EBay is my usual source & whichever supplier is charging the least; they all seem to drop out of the same factory.
Look back about five weeks, Max asked about these & I somehow managed to post a picture.
M