Voltage to + side of Coil?

[Horny Toad]

I am having problems with my rig starting. It turns over fine, but will not fire, no spark to the plugs, unless I jump start it. I thought it was the coil, but I replaced that, still no go. Used the voltmeter to check the voltage to the positive side of the coil & it only read 5.9 volts with the key on. Same voltage to the starter solinoid. I then ran a jumper wire to the plus side of the coil from the fuse box to get 12volts to it & it started and ran fine.

Is it supposed to be 12 volts to the coil? :confused:

I also discovered that there was a Black Widow alarm system wired under the dash & was wondering if it is limiting the voltage to my ignition system? It is a jungle of wires under my dash!!
I plan on removing the alarm ASAP!!

I have a MSD ignition box & Mallory Unilite distributor, so it is bypassing the factory ignition system.

Thanks,

HT :D

[tuckers89GW]

I'm no expert on ignitions, but I believe you should have 12 volts to the coil.

I wonder if you have corroded connections. when you mean jump start, you mean from another vehicle? Where are you attaching the jumper cables to?

I would start by getting rid of all unessasary(man my spelling sucks) aftermarket wiring you don't want to keep.

Man someone with more expertice will have to give better info.

[Bob Barry]

The coil is powered by a resistor wire, so that it sees less than 12V when the ignition is in the ON position, but a full 12V when the ignition is in the "start" position.

It could be that your non-resistor wire to the coil is shot, causing it to get less than 12V while cranking, which wouldn't be enough to start it.

[Horny Toad]

Will it hurt to have 12 volts to the coil all the time?

Thanks for you help,

HT

[will e]

Yes. You do not want 12 volts to the coil all of the time.

On my 73 ford (same starter silinoid as my jeep) the small post near the big starter side post is used to provide 12v to the coil while cranking. After that it drops to a much lower amount. (Once cranking is stopped no power is sent to the small post.)

P.S. this is how you can 'hot wire' you truck. Run a wire from positive on battery to positive on coil. Jump the battery post to the ign post of the starter silinoid and 'ta da' your rig is running. Stearing and Transmission lock outs are your problem.

This is a good fix if your ignition switch is broke, it will get you home.

[tuckers89GW]

guess you learn something every day. ok, can someone explain why the coil doesn't see a full 12 volts all the time? wouldn't it put out a higher voltage?

[Michael F]

The stock coil is not designed for 12v all the time and will overheat and fail over time. To install a 12v coil will cause the ignition module to overheat and fail over time, it cannot keep up with the coil with the extra voltage load. To do the TFI upgrade and run a full 12v to the coil will also kill the module, ford runs a resistor wire to the TFI coil.

If you have a good resistor wire and battery the engine will start (be it not as well) without the full 12v. Not all ford systems have the 12v jump from the solenoid.

Notice I said fail over time, the failure will happen some time it all depends on the condition of the parts and run time. I have had parts fail this way. ;)