If this is the standard Mopar electronic IGN system, check three things.
Ballast resister: You should have .5 ohm resistance on one side, 5.0 on the
other, wires disconnected.
Harness to the ECU (five pin connector with phillips screw) must be
disconnected while ign is OFF.
Pickup coil: resistance across this should be 150-900 ohm, measured at
cavity 4 and 5 in the harness connecting to the ECU, 1 being in the pointed
end. If it fails, repeat test at distributor connection, if its good,
suspect wiring, if bad, replace. Air gap is set using a brass or plastic
feeler (NO steel) to .008".
ECU Harness: IGN ON....Cavity 1, 2, and 3 should show battery voltage +/- 1
Check ECU ground by finding no resistance to ground on number five pin, 1
is in the pointed end. A no ground condition when ground is known to be good
indicates ECU failure.
A bad ballast resister can cause a crank but no start conditon, and cost
very little. ALWAYS carry a spare in the glove box as insurance.
A pickup coil can do this, and it may also cause a hard start when engine is
warm. NEVER use a steel feeler to set airgap, as it magnetizes the reluctor,
causing a no start condition. Brass feelers are available from KD tools,
among others, sold in bubble packs at auto parts stores.
The ECU is usually not the cause, unless it fails to ground. Check ground by
making sure bare metal is on both the case and the mounting point on the
truck. An ECU cost around $25 IIRC, and is also cheap insurance.
Biggest tip: If you don't already, get a cheap but decent multimeter, they
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