Truck Repair: engine/electrical, ford f 150, seatbelt light

Question
I have a 1980 Ford F-150 4X4 351M. Let me try and explain this problem the best i can. My truck quit starting, all it would do was click, the lights wouldnt even come on. Howerver the seatbelt light would. so I repalced the solinoid, Battery, Battery cables, and today put in a new starter. it seemed like this fixed the problem though. The truck finally turned over but the plugs didnt fire. The plugs however were really dirty. So when i went to start it tonite in hopes that it would start, the engine fired for about 2 sec and then quit again. once again the lights dont work, you turn the key and nothing happens the truck will not start. Where is the connection that affects the lights and the ability for the engine to start. I know the igniton module is good. but for it to seem to work and then fail again has me baffled. i hope you can help. Thanks

Answer
Hi Greg,
The ground cable from the battery goes to the engine block, but there needs to be a good ground to the firewall or fender, prefferably both.
They can be from the engine, or from the battery, but they also need to be good, clean, and tight.
The positive cable has a wire through the firewall that needs to be in good shape also, but your description sounds more like a ground.

Van