I have an issue with blowing the fun projects fuse. There is nothing wrong with the fuse holder, but I cannot figure out why it blows and stops the engine. Here is what I can tell you.
The car is a 25 coupe equipped with a dizzy. The car will start and run for various periods of time. Some times when the ignition switch is turned on, the amp gauge buries and then the fuse blows. When driving, the amp gauge will begin to flutter and the blow the fuse. All the wiring has been replaced and I cannot find any rubs in the wiring. I have disconnected all wiring going to unneeded components not needed for the car to run. The switch has been replaced I have not any issues with the starter. The 6 volt Delco alternator works fine and charges at normal rates and steps down as designed. So basically, the only components I have connected are the dizzy and alternator.
The car ran fine until just recently and I have changed items I thought could be potentially problematic.
One question. If I disconnect the wire that comes from the starter switch that goes to the terminal dash strip and use a test light form that wire to other terminal screws, the light comes on as if these wires were grounded. But for right now, sitting in the garage, the fuse does not blow and when reconnected, every component connected to those terminals works as it should. I got to be missing something and any ideas would be welcomed.
Many years ago one of my mentors told me that when electrical stuff is wired correctly, it works. When it is wired wrong it fails. .....
You have an intermittent fault. They can be a bitch to find. One approach is to replace the fuse with a high wattage bulb, with same voltage rating of your system. Then run the car. Eventually the short will show up and the bulb will light brightly. Then start touching wires, looking for the bulb to go out. Eventually you will find the short.
OK: as to using a test light as you described or as I understand it : you're taking the hot or feed wire off the terminal block clipping one side of the test lamp to it and probing the other terminals on the block with the other end. So you're actually powering those circuits. Ignition, lights whatever at a slightly lower voltage because of the bulb/resistor in the circuit. This tells you nothing. These circuits run to ground anyway/normally. Wiring: good. Many replaced parts. Everything disconnected except the dist. and alt. Going by the gauge action mentioned I'm leaning towards the alt going in and out. Disconnect that at the alt. run the car and look for dicey gauge action. If you get none it's probably the alt. I just hope that if you have a working magneto you didn't flash it with your test lamp probing.
No magneto or magnets in this particular car.
Thanks for the suggestions. I will continue to check. I had the alternator checked by a respectable auto electric shop and they said all was well. Bearings were replaced and that was supposed to be the only issue.
A likely cause is a bad coil or coil box wood area that lets some spark wire current/voltage short to the battery + voltage.
No coils in this vehicle as I am running a distributor. ( dizzy)
He has a distributor. No coils or coil box in play.
Tom, I suspect you have a frayed wire after the ignition switch. Check from the BAT lead on the switch to the Coil and from the coil to the distributor. Since it is intermittent it will be difficult to find. It may be easier to just replace those two wires.
The wire loom from the switch to the terminal block is new. Today, I replaced the wire from the terminal block to the dizzy, thinking the same thing you were John. I have not taken the car for a ride after these changes. Be the weekend before I can check it out. For grins, I put a ground wire from the distributor head to the block. May not fix anything but can't hurt either. I just wish it would go to ground once and for all some I can fix the darn thing.
I didn't know the model t ford had a "dizzy" Some people replace a perfectly good ignition system with a distributer because they can't understand the model t electrical system. I have learned the hard way that nothing works as well the original model t components. Check for problems associated with the "upgrades" first. A previous poster said that most of the breakdowns during tours was the result of "upgrades".
Connect a test light (not a led) over the fuse connections without the fuse installed. If you have a short the light will light up. Now move and disconnect each wire one at the time. As the light go out you have found your short.
Maybe this helps
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I would check the ignition switch internally. The re-pops can short out on the casing and the originals can have the same problem. I lined the inside of the casing with electrical tape to prevent this. Just a suggestion but it would explain this sort of problem.
My problem was a loose terminal screw on the ammeter.
It took me a long time to find that problem, as it was so intermittent.
The cardboard insulators had dried out and shrunk.
That also results in a lot of Model T fires, when there is no fuse to blow and stop the current flow.
I put the dizzy on due to issues with the mag. Normally I don't any issues with ignition. Or wiring. This is just a short I've got to figure.
If your car has a steel firewall, check the screws on your terminal block. If they are too long, you might be grounding out at that point. The screw could be very close and only ground when the car is vibrating.