1981 ford f350 New duraspark kills the power

Question

Tried starting my old 81 ford f350 box truck,but turns over won't start,has gas,tried staring fluid etc.

Noticed goop on fender well from duraspark ignition module.Put new one on,turn ignition on,the seat belt light comes on,turn ignition to start,seat belt light goes almost out and engine will not turn over,starter doesn't click,nothing.

Acts as though the battery is practically deas anytime I put a new module. Take the new module off,put old one back on and engine turns over as normal,but no fire.

I have put 4 different new ignition modules on it,will not turn over,acts as though battery is almost dead. NOTE:With old ignition module connected I can turn the headlights on,parking lights,turn signals,etc. Engine also turns over normal with old module installed.

Put a new module on,the headlights nor any other lights will not come on,turn on the ignition switch turn signals wont work either.

It acts as though the battery us practically dead everytime I put the new ignition module on. Four different new modules,same problem.

I've put yellow tab modules and blue tab modules,the truck does the same with all of them The module that was originally on it,when it ran before has yellow tabs and three plugs,one of which doesn't plug into anything,never did.

I've tried same type three plug yello tab modules and two plug blue tab modules(which Orieley's shows is correct) Put the old module back on,lights work,engine turns over,but no fire. Tried jumping the coil,replaced the coil,still same problem. Guessing I'm not getting fire due to bad module,but new module kills all the power.If engine won't turn over with new module,then what? Please Help, Thanks

Answer 1

It sounds like you have got a bad connection some where. The old ignition module is drawing no current, so when you turn on your ignition there is enough voltage to operate any relays you are turning on including the starter relay.

However with the new module connected, it is obviously drawing enough current to cause a large voltage drop across the bad connection which means nothing else will operate.

You need to use a voltmeter to check the voltage on the various circuits to try to work out where the bad connection is. This will need to be done with the new module connected and the ignition on.

I would make a start checking the voltages at each of the fuses. For it to affect so many circuits, it should be easy enough to find. It is also possible it is a bad earth connection, but I think more likely on the positive side. The battery connections are obviously ok because the starter works.

It is also possible that the ignition switch is not making a good connection, so you could check the voltage both sides of the switch.