Replacement flasher unit for Series IIA - replacing Tridon F550

[IIA]

I think I need to replace the flasher unit in my 1970 IIA (or if anyone knows how to test the old one, please explain). The one I pulled out is a Tridon F550. Does anyone know what an equivalent replacement would be? I don't see anything obvious form our hosts.

[Les Parker]

Is the Flasher a 2 pin or 3 pin relay?

Here's the 3 prong style :-

http://www.roversnorth.com/ProductDesc.aspx?code=PLC158

[IIA]

Is the Flasher a 2 pin or 3 pin relay?

Here's the 3 prong style :-

http://www.roversnorth.com/ProductDesc.aspx?code=PLC158

Mine has 3 prongs on the bottom and fits top-first into a clip in the dash panel. I can't tell from the picture whether the one from RN has 2 or 3 on the bottom. Is the thing on the top just for attaching it?

[stomper]

Napa part number NF 550.

[IIA]

Thanks for all the responses. I ended up going with a NOVITA EL13 because my local auto parts store had one and I like the see-through case. (Obviously the most important feature - [sarcasm])