2006 mitsubishi endeaver ECU goes out withing 500 miles of being replaced. has had 8 ECUs in 4 years and no high beam head lights when it goes out. What is cause?

BUT NOT TOLD DO HEADLAMPS FAIL TOO, LOW AND HIGH BEAM
seems the battery in car is weak to me.
CHECK FUSES FIRST?
THE CARS FRONT ECU CONTROLS HL RELAYS.

HL dead is big problem. IF TRUE
got DLR,????? daylight running lamps option., say in CANAda?
so engine runs, ok?
HL failing , ? so key off, do head lamps work
HL work ,key on and key off even lost the key HL work for safety max.
CHECK THE BATTERY VOLTAGE RUNNING,(DMM METER CHECK)
13 TO 15VDC IS NORMAL.
BELOW 13V the BCM BODY BRAIN GOES MAD.(CALLED FRONT ECU ON THIS ODD CAR)

you posted only what fails not the good, what things do work;.
engine and all other things. (most)
i bet alternator died or battery is bad. the first caused the second..

This is reminiscent of a Volvo I tackled a few years ago where the lighting was controlled by an electronic control unit buried behind the centre of the dash. The owner was unwilling to part with the hundreds of pounds a replacement would cost and planned to change the car instead.
I managed to rig a temporary switch that made the lights work, though can't remember quite how.

Modern cars using CAN-bus networks work in a similar way to that older Volvo where the various switches do not turn on lights, wiper, heater, etc. but tell a local ECU to send a signal out on the network instructing various other ECUs local to whatever needs to be activated to do the duty and switch on.
If this describes your car it will need investigating with dedicated diagnostic equipment before examining a wiring diagram.

If your car is of an older vintage it would be wise to begin with the wiring diagram.
Good luck!

When either the high or low beam light is out in either side, DRL (daytime running lights) indicator will come on. When one bulb goes out, that's a clue the opposite bulb will burn out soon, so its best to replace both bulbs. If it was a fuse issue, both left and right side would be out. If driver side is OK but passenger side is not, then its a bulb issue. A 2006 Honda civic takes 9006 (HB4) low beam bulbs and 9005 (HB3) high beam bulbs. Cheapest is online from Walmart site-2-store. After procuring, wear latex, vinyl, or ANY gloves to keep your (corrosive) oil skin from coming in contact with headlight glass bulbs. Your skin oil will chemically react and cause shorter life span on glass bulbs. Instruction don't tell you this, so you handle with your hands, then need to replace bulbs 3 years later instead of 5 years (or more) in the future. With gloves on, pop the hood and look behind each headlight. Turn counter clockwise to unlock headlight bulb holders. Its a quarter to half turn to unlock bulb holder lock. Replace one bulb at a time so you don't confuse high beam from low beam. The wire has a tab you need to lift to pull out & disconnect wire connector. You might need a slim narrow-**** (NOT phillips) screwdriver to lift the tab; or use your house key. Snap the wire connector to the new bulb, then twist into headlight housing to secure bulb holders, then move on to the next bulb to repeat the procedure. Pict below, 9005 high beam is on the left, 9006 low beam is on the right. Handle by grasping the plastic base, not the glass bulbs. The raised potrusion on the bottom center is where the tab locks onto wire connector. Replace all 4 bulbs now, but in the future, its likely the low beam will wear out before the high beam. In the future, replace only the pair, not all 4. The factory installs inferior bulbs that go out sooner, hoping you'll take to dealership and they ******** you with higher parts-n-labor fees. As opposed to Walmart online site-2-store, it would cost you AT LEAST triple in parts & labor from dealership to replace all 4 headlight bulbs :-(

Could be a defective headlight relay, Located in the fuse block in engine compartment,

I would start by checking the bulbs, if the bulb goes bad you can still have high beams, so start by checking the bulb and the fuses if they dont light up after replacing the bulbs , hope this is helpful,

I believe that relay is up under the dash by the passenger's side (above where on eplaces their feet) Just a heads up though; if you're not getting fuel I'd check for injector pulse. Given the year of the truck there is a good chance the ECU has failed. Early 90"s Mitsubishi's had poor capacitors in the ECUs. Remove and open up the ECU look under the three (3) capacitors, if they'er leaking you'll see a light liquid on the circuit board under the caps, often with a green hew to it.

I hope this may have assited,
Tom

It seems like you have a bad ground wire or a short.

The quckest way to fix this is to fit a relay to your high beam light circuit. This will feed power directly to your high beams and cut out the high resistance of switch and wiring.

sounds like the problem is the dimmer switch, get a price on the dimmer switch. If you have to, get one at a junk yard . It's cheaper.

Check for headlight relay and fuse. Some cars have separate circuits for head light flasher and normal high/low beam. From your description, I would suspect a bad connection to/from relay or relay itself.