We've been driving around with Volt HID kit for several months without major issues, but I've come across several threads where people recommend relay kit with HID kit.... Ordered a relay kit ($40), but learned that 2 sets of wires must be connected to the battery. This makes engine bay a little messy... Is relay kit really necessary?
Yes, to protect the wiring & get maximum brightness from the bulbs. I just did a HID retrofit on my 09 Corolla & wired in the harness with relays. You can see the relays in this pic.
Necessary? I would say no since the stock wiring provides enough power for the bulbs. I think the Volts would look exactly the same whether the power came from the existing wiring or from a relay since they are a quality set. Not sure what a Corolla draws power wise, so can't really compare what a Volt set would do on there. That being said, I think for piece of mind the relays would be a good idea. I was thinking about it on my set, but I think I am going to weight until they finally die (if that ever happens) and upgrade to the Xtreme Digital Kit since they have a 5000K bulb option.
If your kit is 55 watt then you don't need a relay. The Prius "expects" 55 watts, if it doesn't sense 55 it may think the light has not been switched on and won't supply power or supplies it intermittently. If you have 35 watts then you may need relays, however if you are experiencing no problems then why worry?
Kit is related for 35 watts.... I've had an issue with module going bad, which resulted in passenger side bulb being on all the time (even with power off). Module was replaced by dealer under warranty. Not sure if these issues are related or not... Volt HID Digital+ HID Kits
Though it may not be "necessary" the start up of an hid bulb draws a huge amount of power. The stock harness may handle it just fine. However, if something goes wrong, I'd rather melt a relay harness than my oem harness any day. The harness serves as cheap insurance. Clean it up with a bunch of zip ties if you are worried about it being messy.
I'm running the Volt HID Digital+ kit, too. The inrush current at startup is spec'ed at <6 amps (each ballast), so there shouldn't be any problem with running without a relay harness. Steady state draw is about 3 amps, so we should be fine. The fuse protecting the low beam circuit is a 40 amp, so we are well within the design rating of the factory wiring harness.
