250-500cc What's this part?

In the pic, what's the silver part with a built-in heat sink? I assume the black plastic part above it is the coil? 2009 WR 250.

Looks like the voltage regulator to me?

Yup, and hopefully on your WR it's a regulator/rectifier

I wonder if it is a rectifier (8000H3964)? Correct me if I'm wrong, but that would be converting to DC somewhere in the circuit?

If it's a rectifier it should have four wires? And a regulator would have three?

If you look here it seems on your bike it only has 2? and the part # is 800075343
http://www.motosport.com/dirtbike/oem-parts/husqvarna/2009/wr-250/electric-part?fam=
The "enduro kit" page has the rest of the wiring harness and other bits. My understanding is all WRs should have a R/R, but maybe some didn't
Seems like mine has 3, ground, line from stator and output which is yellow, but I'm not home yet and can't look.

800075343 is the CDI Ignition Part number. I wish I knew more about multi meters. I think there's a way to check if AC or DC is coming out of the box.

EDITED.

If you have a multimeter set it to dcv, have the R/R wire (yellow?) hanging out where you can get to it, start the bike, black lead from the meter to bare metal, red lead from the meter to the connector from the R/R, should read @ 12v

That is the standard Husky WR regulator. Not a rectifier.

This site never ceases to amaze!

you arent kidding when you say standard. looks like the same one on my 95!

Yep, I have a brand new one sitting in a box in case I ever need it.

If it ain't broke don't fix it! It's the KLR of 2 stokes!

Wally's right!
The WR's run approx. 12V AC for the lighting circuit

An those OE husky regs are pretty sturdy unit too!!

BTW folks, the reason I ask is because I'm attempting to install a "factory" enduro kit -- without instructions. The only thing is that I want to replace the bulbs with LED, so I need a rectifier. I've seen in the parts catalog that some of the non-usa enduro kits came with a rectifier that looks almost exactly like the regulator in my picture, so I was hopeful that mine was a rectifier. I suppose I can get one off ebay, I'd just have to figure out the specifics in terms of voltage and current. Unfortunately I know very little about electricity.

This reminds me of a project I did to convert my $90 harbor freight A/C flux core wire welder to D/C. I had to put a rectifier in after the transformer and run that to a capacitor. It was an easy project but all the parts were listed on a forum so I didn't have to figure out the sizes ;-)

Well, now I'm doubting mine is an R/R. I've got an LED headlight to add as well and assumed mine was an R/R.

This thread may help you a little, last post has a link.
http://www.cafehusky.com/threads/wr-250-lighting.21742/