My truck starts but will not run. New ignition switch, pickup coil, plugs, wires, cap, rotor, coil, ignition module. There is voltage to the coil with the key in the run position. The engine will start and continue to run as long as the key is held in start position, then dies as soon as key returns to run position. The voltage to the coil reads 12 volts with the key in the run position. I am getting fuel to the carb, and can actualy drive the truck as long as I keep the key in the start position. It was thought that a new ignition switch would solve the problem but it didn't. Does anyone have any idea what could cause this?

DC

 

well when u start your truck with the key on the start position it i giving the coil full 12 volts and when u release the key to the run position it would give 8 volts to prevent the coil from overheating i'm not sure where the resistor is or if there is a resistor like the old dodges used to have or not. i would try to get a wiring diagram to see what all connects to the coil positive wire

 

Check out the starter relay and wires going to it, an open/short in the starter circuit can cause what you're describing, especially since it will stay running in the start position.

 

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Sounds like the resistor to the ignition is open. Check it at both ends with a test light and the ignition switch on.

 

Does your radio operate? Your heater? all of the stuff that normally is on in the run position, guages etc? If so, then I would guess that either the resistor wire from the ignition switch run circut to the coil is bad, or broken, or you have a bad ignition switch, or the ignition modules run wire is broken or you have a bad ignition module.

If none of the stuff, radio, heater, etc, works then I would guess that the ignition switch is bad, or you have a bad fuse link somewhere.

When the ignition switch is in the start position power is supplied to the starter solonoid, the ignition module's start wire, computer if applicable and the coil, the brake warning light, oil and amp lights if applicable, and that's about it.

When the ignition switch is in the run position. power is supplied to the same components but along a different wire or wires to the ignition components, except the starter solonoid. It goes through a resistor wire to the coil, and a different wire to the ignition modules run wire, computer, the heater blower, etc.. Then yet another wire supplies the radio, windshield wipers, guages and turn signals etc. It has several run wires so when you put the ignition switch in the accessory position, only part of the run circut is active. Radio, guages, wipers etc...


Think of it this way. In the start position only the components that require the engine to be started is active.

In the run position, everything is active.

And in the accessory position, only selected parts of the run circut is active. I.E. not the ignition portion for one.

Isolate which part of the run circuts still are active, and which ones are not, and you can narrow down your problem quite quickly.

Another very slight possibility it could be is that one of the hot wires from the starter solonoid that powers the whole truck has been put on the wrong post of the solonoid. Does your headlights work for instance, or do they only work with it in the start mode too? I've also seen this happen. Turn the key to start, and the lights and truck runs, put it in the run position and it tries to start, etc...

Hope this helps.

 

turn signals not working in the run position indicates no power in the ignition switch. A remote starter trigger will help in diagnosing this too.

 

Ok You have helped me narrow it down. I have eliminated the starter relay as the problem. The relay, connections and wiring to and from all check out. I ran numerous tests today and everyrhing seems to be pointing to the resistor lead. Fords after 78 with the duraspark II ignition no longer used a balast resistor, replacing it with a resistance wire. Getting battery voltage at the coil is a good indication (so the manual says) that the resistor lead or the coil are bad. The coil is new but as Bdox points out new just means new, it doesn't mean good.

Thanks for all the input. I'll let you know how it goes.

 

All you need to do is to check the voltage at the +side of the coil with the key on. No voltage there leads directly to an open circuit. The first componant back from the coil + is the resistor wire. If the coil + shows no voltage, locate the resistor wire and read the voltage (key on,) at the other end. You should have voltage there. If not, the next place to check is the ignition switch connector. That could be loose or corroded.