Where exactly are the heating elements in the PA-28-180's pitot mast?
You don't actually need to get into the mast to know if the pitot heat is working. I fly a PA-28 and during your preflight check if you engage the pitot heat and allow it to run for a minute or two the pitot tube should be warm to the touch. If it is not your pitot heat is not working (or is not reliable enough for flight).