f350 glow plugs and ignition switch

You'd probably be best served to subscribe to a service such as this:

http://www.chiltondiy.com/

I changed my share of glow plugs on the 6.9-7.3 series motors. On the engines before the electronic unit injectors, you could just get a thin wall 7/16" six point socket and a 6" extension connected with a flex joint. The angle of them was almost straight up. Caution, use lots of penetrating oil. These plugs are going to be rusted in there. Another word of caution. As the glow plugs overheat, they will blister and swell. They may get wider than the hole they need to come out of. That is where the penetrating oil helps. You just need to keep twisting and pulling till it comes out. After you have the plug out, turn the engine over to be sure all the penetrating oil is out.

You can test the glow plugs a couple of ways. The first is with a timer. If the glow plug timer is cycling them faster, it is because there is less total resistance in the glow plugs. The other way is to pull the wire off of the glow plug, and testing the resistance between the glow plug wire terminal, and ground. If my memory is correct, it should be 1 ohm. Test a new one to be sure. Good luck.