Wazuans, I have a weird problem with my headlamps(dim ones-xenon(Premio new model)), I have tried several mechanics but nothing is working. These lamps turn on ok at night, but one goes off after like 3 mins even if just idling. When you switch them off and back on, they light and then one again goes off(random bulb). Also when they cooperate and light for a while, while driving, then you apply emergency brakes, they go off. But when I hit potholes etc they don't. I have even changed one bulb -for 2500- but turned out not to be the issue. They are not loose. The full lights(normal halogen and different set of bulbs) work OK but you cannot drive always with full lights. Any good wiring mechanic anywhere? I am contemplating Toy E.A but I believe I can get it fixed somewhere without incurring the huge bill (imagined) at Toyota EA.

I had this very problem with one HID lamp, white, would go off after 10 minutes of switching on. It so happened that the lamp had reached the end of its life, the crystals inside had turned milky white (instead of the usual brown color). The remedy is to buy a new one. Go for Philips d2s/d2r depending on the housing. German, will last a good long while.
If the crystals are ok and the bulb has no fractures, then have someone check the ballasts. Well functioning ballasts produce a loud cracking electric arc when the lights are turned on with the buld removed, accompanied by an acrid smell of air being ionized. If its the ballast you might have to buy an entire lamp. All the best.
Caveat: I am not a mechanic, I got this as I watched mine getting fixed.

Thanks @quicksand
Kindly share the contacts/location of your mechanic... Interestingly one bulb is new, but still also goes off, but the older one(came with the car is more notorious). I don't have money for a new headlamp, kwanza hii May - a mech told me its 60k.

0705361206 His name is Evans, based hapo Baricho road.
As for the lamp costing 60k....ingia OLX. Lots of stuff on sale, very good bargains...and the car parts you will find its a parts shop. I am sure you can find one for much much less....if the cost of replacing ballasts is comparable to buying a used lamp, go for the lamp..just have it tested thoroughly first.

It could also be a naked wire touching on the car's body thus short circuiting the system ... had a similar problem the low beams would short circuit but the high beams would not ... it could be a wiring problem or the metal cases holding the light acting as a ground thus short circuiting the system ... good luck as you sort it out