Transact-sql Code Does Not Work. HELP!

Hi all, I am new to transact-sql and hoped that someone here might be able to help. I have a db with a field called "part" ... part contains text in the format:

xxxxx-xx-xxxxx

(the number of x's before or after each hyphen vary) such that I could have xxx-xxxxx-xxx as the part.

Someone wrote this transact-sql to take my current "part" field and move it to three different part fields ... a,b,c

If xxxxx-xx-xxxxx was the part in the original db, then a would contain xxxxx .. b contains xx ... c contains xxxxx

Make sense? Here is the code. It doesn't work and I can't seem to figure out why! It looks like it is just trying to find the hyphens and cut out the text from that... but it fails with an error that says "invalid length parameter passed to the substring function". Note, if I take off the "-1" from each line below... then the function works but produces the wrong data.

char(45) = "-" (hyphen)

UPDATE [dbo].[parts] SET
a = SUBSTRING(part,1,CHARINDEX(CHAR(45),part)-1),
b = SUBSTRING(part,CHARINDEX(CHAR(45),part)+1,CHARINDEX(CHAR(45),RIGHT(part,LEN(part)-CHARINDEX(CHAR(45),part)))-1),
c = SUBSTRING(part,CHARINDEX(CHAR(45),RIGHT(part,LEN(part)-CHARINDEX(CHAR(45),part)))+CHARINDEX(CHAR(45),part)+1,LEN(part))
GO

Does anyone know what I can do to fix this or is it much more difficult to do than what it seems?

Thanks!