New DDM HID turns off itself if I turn headlight on first.....

Since the Prius doesn't have a starter, the initial power up is only 30-40 amps. This is not enough discharge current to drop the voltage significantly to cut out the HID. My advice is to add a relay with heavier guage and power it from the white primary wire in the fuse box.

 

Yes I mean the initial power up. Some ballasts react differently when there's a voltage drop. There's a 6awg white primary wire in the fuse box that's connected directly to the battery in the hatch. There's no need to run another wire to the battery.

 

I have the same brand and wattage setup as in your car. I never turn on the light before starting the car but usually was the driver's side didn't turn on (didn't have relay harness at that time). I live at San Diego, so I drove to the DDM's store and spoke with the technical support in person. He said there wasn't anything wrong with both ballasts (even thought it was always on the driver's side). I was doing some troubleshooting so I bought the $12 relay harness to hook up directly with the accessory battery from the fuse box under the hood. However, the problem didn't completely go away until I swapped the bulbs with the passenger's side. This made me feel like there is some problem with the left ballast. DDM products have lifetime warranty, but they try hard not to exchange you a new one unless problem keeps happening in a roll or failing their tests. I use DDM on 2 of my cars and they seems to be find with the price I paid ~$55 include harness. Wiring is not difficult at all. Just open up the under hood fuse box, use a 10mm ratchet wrench to loosen the (+) from the accessory battery underneath another black plastic cover (not the big fat white wire I mentioned before) and ground. I can take some pictures of my setup tomorrow if you like.

 

Question-DDM has HID 55 watt bulbs. Would a battery harness be needed with these? Have asked Toyota dealers and they don"t know.

 

I purchased the relay harness just to be safe. I have not installed the head light kit yet because I have factory HIDs and that complicates thing s. My 35w Hids for foglights installed very easily once I figured out the Prius uses reverse polarity.

 

The OEM H11 bulbs are 55 watts but I am afraid to go for a 55W HID although it may be compatible. A 35W HID set is already 3 times as bright as the 55W halogen bulbs, using a 35W HID may be able to save some juice for the motor. Following pictures show where I put those DDM ballasts.
Under hood fuse box (Don't connect to the big fat white wire but the terminal under the cover)


Driver's side ballast location (why didn't I hide it next to the left fender similar to the one on the passenger's side, I don't remember. Location is totally up to your choice.)


Passenger's side ballast location


Relay harness

 

I just finished installing the DDM Tuning 55 w HID kit in place of the stock 35w kit. I'll keep you posted if I end up with similar problems. I installed the relay harness so I should be trouble free. I went with the 6000k bulbs to try and match my foglights.

 

I've got the exact same problem. I'm using a DDM 35w kit for low beams. Using a DDM wiring harness too. Periodically, passenger side goes out. I cycle the headlight switch and they come back on. Sometime they stay on other times they'll go out after a while. Did you (does anyone) have a verified solution to this issue? Thanks.