Low Voltage to Coil. No start (1 Viewer)

[ChristmasMud]

I am having a very difficult time with my '73 1F. I had it running a few weeks ago and then it stopped working. I had burned the points at this point as well so I decided to upgrade to electronic ignition at that time.

Now I have minimal voltage to the coil +/- 4 volts with the key on. Battery has 12.5 volts. Engine cranks but no spark at the coil or wires.

Current setup is a Pertronix II coil and electronic ignition. I also swapped in a spare ignition switch but no change.

I've checked the grounds for the battery and they're good.

Help!! I'm at a complete loss for this.

Update:

I was able to get the truck started by running a hot wire from the + battery terminal to + terminal on coil. I also replaced the ignition fuse before hot wiring it and it didn't fix the issue.

 

[CHCP]

you must have a pinched wire between the 15a ignition coil fuse and the coil. In the 1974 wiring diagram it shows a direct wiring from the fuse to the coil. I'd also take the fuse out and read voltage on the hot side of the fuse holder just to make sure you are getting 12vdc to the fuse, put the fuse back in and take a voltage again if its low then it would confirm a partial ground.

 

[JAFO2014]

Disconnect the wire going to the coil. Measure the voltage at that wire. If reading the low voltage ( +4 v or so) then as said, something is acting like a resistor causing a voltage divider. Pinch or corroded connection acting as a resistance to current flow. Track it down.

 

[edwjmcgrath]

How is this wired? Do you have a bypass resistor? Not needed if you have the pertronix coil and ignitor.
Post a picture or drawing of how it is wired.

 

[ChristmasMud]

Thanks guys for the advice. I'll start to trace the wires tomorrow.

@edwjmcgrath it is not running an external ballast resistor. I'll take a picture of my current setup tomorrow. You'll note in that picture it'll have the temp hot wire from battery to switch to coil so that I can drive the vehicle for now.

 

[edwjmcgrath]

The wiring should be pretty simple. If it's the original wiring, there should be a BY colored wired going to the coil positive. When you removed the points, you should also remove the wire running from the coil negative to the distributor. The pertronix comes with two wires. Red connects to the Coil + (where the BY is) and Black connects to Coil - (Where the wire you removed was).

When you measured the voltage, what did you use as your ground reference? Was it the engine or frame or battery terminal?
When you checked your ground wire did you check both the battery negative to frame AND the frame to starter/engine wires?
People often forget about the second one and that can cause some unusual effects when faulty.

 

[ChristmasMud]

@edwjmcgrath I will have to double check the ground at the frame/starter. I had thought since it was engaging correctly that that ground was fine.

Also, you pointed out something I missed in the install. I had attached the black cable to the negative side of the pertronix coil thinking it was the needed ground. It doesn't run directly to the distributor and used to hook to the - side of the old coil. Is that causing my resistance?

 

[edwjmcgrath]

I'm not following you on the black wire but it sounds like it may be miswired.

The way points wiring works is that you put 12v on the coil positive and connect one side of the points to the coil negative.
The other side of the points is grounded through the body of the distributor. When the points are closed, the circuit is complete and current flows through the coil.

You can think of the pertronix ignitor as a set of points that also needs power. The black wire on the pertronix goes to the coil negative and the red wires is the power to operate the pertronix.

The old black wire that used to connect to the points goes away and is replaced by the new black wire that is part of the igniter.

 

[Pin_Head]

Don't bother measuring the voltage on a disconnected wire / open circuit. It will always read battery voltage because there is no current flowing.

Run a hot wire directly from the battery + to the coil + temporarily and see if it will make a spark. If so, the wiring from the ignition switch is bad. If it doesn't run, then the coil or ignitor is the problem. You can test the coil by disconnecting the wire on the - side of the coil and momentarily grounding the - lug of the coil. You should get a fat spark every time you interrupt the ground.

 

[edwjmcgrath]

Pinhead, he already did what you suggested (see his "update" in the original post).
It runs while hotwired, so there's something wrong with the ignition switched power wire (or the way he's connected it up).

 

[Pin_Head]

OK. It is pretty simple then. Bad ignition switch or bad wire from switch to coil. There is no ignition fuse. The engine fuse is not for the ignition.

 

[edwjmcgrath]

I didn't think there would be a fuse either, but this schematic on coolerman's site shows one on the 73.

http://www.globalsoftware-inc.com/coolerman/fj40/schematics/FJ40/1973FJ40/73JF40.jpg

 

[Curt]

He said he replaced the ignition switch with a spare hmm.

I want to see pictures of how the dizzy is setup