test on truck's ign.coils good or bad?

My 1998 Ford F-250 truck broke down. I suspected that the two ignition coils are bad. How I can test it if the two coils works or bad? I use strobe light goes to coil where the spark plug cable tip at and other clip to negative battery while I crank-up, is it works? I did test and not flash light on while I crank-up. It means bad coil, Correct?

I usually test by removing the coil HT lead else a splug lead and holding its end ~10mm from the grounded engine or body whilst cranking the engine. BE WARNED however that that can damage certain (primitive) electronic ignition systems, and the HT lead must be suitably insulated from the holder (its 40-80kV kick is somewhat higher than the 0.2kV from a mere relay coil!). Both above can be hazardous - both to equipment and people. Some have been killed by ignition systems. If there is no spark, it might be a power or trigger situation and that has various checking steps and procedures. Note however that these tests may not detect intermittent coil failures - eg, open coil winding when warm/hot, or internal shorts etc. A good spark should jump at least ~6mm in free air. (A sparking free-air splug does not mean it sparks under compression.) My system sparks well over 20mm in free air (at the splug ends, ie, after the distributor).

Is it a gasoline engine?

Well since he mentioned spark plug wire. It is just rare to see a 3/4 ton gas burner.

Yeah. I can't say I can recall any diesel ignition coil problems - even on 2 strokes. But my ute is under one tonne (yet can legally carry a load of 1400kg) and it's a gasser. I'd assume it's a V8 F250, hence maybe the twin coils...

yes 5.4 triton gas.

yes, it is twin coils...