It’s so big and so ugly.
Yes, and worse: it is utterly unreliable. There is a better lookalike (much more reliable, slightly smaller) that is much used in campervans aka WoMo’s aka mobilhomes aka campingcars &c &c but then one must redo every single plug and every single receptacle… OK for campervans, but in the air one would wish an alternative drastically smaller and much more reliable.
Funny observation, though: my homebrew electronics get rather shaky power from the standard cigar lighter plug in my Italian made van, but are acceptably reliable when plugged into my Hungarian built microlight.
Why the car lighter outlet is still used as power outlet even in modern car? It’s so big and so ugly. But still can be found in every car instead of (or together with) modern USB… Perhaps, some compatibility reasons?
Apart from cost (which is IMHO barely relevant on the scale of aircraft costs generally, and well worth it to save hassle in years to come) I think the biggest issue with milspec circular connectors is their overall length which, by the time you have added in the cable guides/clamps/whatever can be 75-100mm in total, for the two mated halves, and there isn’t always room for that, or it isn’t easy to secure it to something fixed. You can’t (well you can but maybe shouldn’t) just wrap up the connector into the harness.
One could use these connectors without the accessories, and with just heatshrink over the soldered pins, and then they are much shorter. But that isn’t “proper” 
Also they would not be sealed anymore but in most cases in the real world they aren’t sealed anyway, due to some incorrect practice in the wiring.
Socata have used some milspec circular connectors in the engine area, but curiously they have downgraded to the crappy AMP circular plastic (non sealed!) ones in the landing gear squat etc switch wiring (which is basically exposed to the elements when the gear is down) and downgraded further to the totally crappy Molex ones for things like wingtip lights.
D-conns are popular because they are cheap and light, but it isn’t easy to find cable shells which are compact and don’t have sharp edges, so you still end up with a big connector if you need say 25 ways. I have found some very compact DB9 shells, and Positronic do some nice ones in their outrageously priced connector ranges. D-conns are good because for about 10 quid each you can get heavily gold plated ones.
Re ACF50, I do the whole plane (not cockpit areas, due to the smell and mess) every year or two. They recommend every two years. The total used is about 1 litre, which is maybe 50 quid. I bought the proper spray kit from a guy with an R80, Aston Martin and a Maserati and 3 planes who bought it and then couldn’t bear to make his planes dirty with it
Those white plastic connectors a used quite often, they are not too bad on aircraft which sleep inside. Corrosion often happens to aircraft which stays outside for long periods of times. Leaving your aircraft outside is not such a good idea anyway if you would ask me.
I think keeping a plane inside can save money on the long run, on corrosion, paint, electronics etc.
On these white, and SUB-D connectors often the weakest point is the support of the wiring. It is very important to support the wiring, as Peter indicated before. This is the number one failure on wiring.
The MIL SPEC connectors are bulky and heavy. They can be fine when used on a bulkhead, but not for inline connections. These white ones are used as inline connectors all the time. MIL SPEC are therefore not a good alternative.
I do prefer good quality SUB-D connectors, which are quite common in aviation / avionics nowadays.
There is not the slightest bit of corrosion, that would be too bad only three years from new.
ACF50 is new to me, I will certainly give it a try. Not cheap, though, at some 15 quid per can.
But the mil spec connectors look like massive overkill – do not forget this is minimalistic technology, and NO electricity is required neither for flying nor for landing. Motorbike components are used for ignition (Ducati) and for the starter (Suzuki, I believe), and everything should be more or less at the same level.
Curiously I have never seen these before so I must revolve in the wrong social circles.
I would chuck them out and put in some milspec circular ones. They come up on Ebay.
OTOH if they are not actually corroded then spray some ACF50 on them.
Thanks very much, you are a better www-searcher than myself apparently… They quite look like less-than-brand-new telecom equipment, and as my machine was made in Hungary the Comecon connection is not unexpected. But if they seem reliable enough there is perhaps no real need to replace them.
Karel, as far as I know, these connectors are originally from the telecom industry – electromechanical telephone exchanges used them by the thousand. Judging by the fact they occurred on both sides of the Iron Curtain, they were quite popular in their heyday. I seriously doubt they are still being made, but you may be able to find some new old stock.
Update: they seem to be still made in Russia, but only in 5-, 10-, 16- and 30-contact versions. Contact pitch lengthwise is 6.1 mm. They are also available in an IP54 version.
Removed the instrument panel from my own pride and beauty and found no less than four couples of M/F connectors of a type called DS121, the 12-way model. Are these still currently available? What do people think about them?
They are obviously not designed for the aero environment, seeing the spec they carry: 350Volt 10 Amp (but no mention whether that is DC or AC)
They look quite good to me, but they do require soldering which we (well, at least some of us…) prefer to avoid.
For a picture: see http://www.ebay.com/itm/30-PIN-INDUSTRIAL-RECTANGULAR-CONNECTORS-350V-10A-SET-DS121-130-1-01-DS121-130-2-/151127197216 which shows the 30-way model with 3 rows of contacts, mine have 2 rows.
The milspec circular ones are usually sealed.
I'm not convinced about these connectors. I have a MS3116 connector in the cockpit. That flimsy bit of rubber neither aligns the pins properly nor does it hold them in place securely. Connecting it is always a hassle and I regularly have to reinsert pins.
They might somewhat work if you build your own cables out of individual wires and mesh or hose but they certainly don't if you use ready made cables.
I'd prefer a good D-Sub (with gold or berrylium bronze plated machined contacts) over the MS3116.
