Glow PLugs and Relays

the fuel pump and timing belt are not components for spark did you check distributor- points -coil -plugs-wires ignition switch -fuses and relays ----didnt specify engine if diesel need to check glow plugs

The wire that runs to the glo-plugs comes from the relay and as it is a heavy gauge wire (colour coded ) try tracing it back to a relay. IT may be completely separate to all the others.

I would be inclined to replace the relays as it appears that there is a shorting fault in the relay coil that is not allowing the points to be held together for the correct time period.

Does the engine start and run ? There is a fairly easy way to check all glow plugs.

http://www.youtube.com/watch?v=4TcuJDd9Hho

that must be the automatic relays that control the glow plug supply. determine the relays condition.

there is a glow plug relay mounted to the rear of the engine try jumping across it to run the glow plugs and see if it will start then (these relays fail quite often)

This could most likely be one of 2 things, 1. if it is your maintainance light, it is probably one of your sensors, possibly the mass air filter sensor, oil pressure sensor, and 2. If it is a diesel engine and its the glow plug light, you would need to replace your glow plug relay because it telling you that the glow plugs are still on when the engine is running, which you should take care of asap before you have to replace the glow plugs themselves.

no this will not improve the performance of your diesel, the glow plugs are used to ignite the fuel at initial start up and then they turn off.

The relay should cost about $35-45. A common Ford Starter relay can be used in place of the official glow plug relay. All that is required is a relay with terminals that have 5/16 or 3/8 terminals and can carry about 150-200 amps. When all 8 glow plugs turn on, it draws about 150 amps is all. There are two relays for the 7.3 diesel. One energizes the glow plugs and the other energizes a heating element in the air intake. That one is used to help eliminate white smoke while warming up and is turned on and off by the engine computer. It is usually only called for when the temperature is 20 degrees F or lower.
Otherwise only the glow plug relay works.