Mechanical fuel valve, you can find these on Ebay in "boat parts". Also look at "marine parts" stores on the web. At Ebay, simply use "fuel valve" for a search, then click on "marine" or "boat" whichever Ebay provides on the left side. On the web, you will have to go right into web sites then search for this valve inside the store. Lots available, just have to search a bit in Ebay or inside an online marine parts store.
Electric fuel valve, well, just pick a truck brand and go to an authorized dealer on the web. Ford has a nice unit, single wire operation. GM, Dodge, have their units, just as nice. Best to go straight to a dealer, like Ford, then search inside their store "fuel valve" to get returns. You can buy directly online or pull a part number then order from Auto Zone, whatever. Easier to buy on the web.
Takes a bit of searching but you will find what you need. Just aggravating to have to sort through so many parts.
Billyray
