How to calculate the position of the sun in long/lat?
By latitude and longitude of the sun, I think you mean latitude and longitude of a point on the earth's surface where the rays of the sun fall perpendicular to the surface. 

In astronavigation, this point is called the Geographical Position (GP) of the sun and terminology to describe this point is slightly different:-

Latitude of the GP is called Declination, and it is numerically equal to what one might call "Latitude". It is measured in degrees North or South the equator. 

Longitude of the GP is called Greenwich Hour Angle (GHA). Just like longitude, GHA is measured East or West of Greenwich Meridian. 

Describing the sun's position in this way is called the Equatorial Coordinate System.

The Wikipedia page you have used gives the additional formulae below to convert from Ecliptic Coordinates (the steps you followed) to Equatorial Coordinates. 



Follow these steps to determine Declination $\delta$ (Equivalent to Latitude).

To get the sun's GHA, you need to first calculate $RA$ (Right Ascension) as shown above and then convert this to GHA by these= rules...

$SHA° = 360 – 15 · RA[h] $

$GHA_{Aries}° = 15 · GST[h] $

$GHA = SHA + GHA_{Aries}$

For the second step, you will need $GST$ (Greenwich Sidereal Time) which is you can calculate if you know UT (UT can be obtained from the time shown by a clock). Use this link to convert directly from UT to GST

If you want a simple, concise way to be able to calculate the positions of all manner of celestial bodies, the sun, moon, planets, stars, then I highly recommended the book Astronomical Formulae for Calculators by Jean Meeus. It is the simplest, most comprehensive collection of astronomical formulae you are likely find anywhere on earth.