Blows a fuse when starting

G

G Bennett

New member
My 1929 A has a 20 A fuse on top of the starter. It has started fine but now blows the fuse as soon as the engine starts cranking. Where do I look?
 
G Bennett said:
My 1929 A has a 20 A fuse on top of the starter. It has started fine but now blows the fuse as soon as the engine starts cranking. Where do I look?
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`20 amp not much- I use a 30 amp. maybe to small? Did this just start blowing the fuse? Could be the starter switch also?
 
Running the starter shouldn't blow that fuse.
Maybe its your brake light switch.
Do you put your foot on the brake at the same time you start to crank the motor over?
 
As crosscut said, running the starter should not blow the fuse. As Gary said 20 amps is too small. Use a 30 amp fuse. Do you have the original foot starter switch or a more modern solenoid? If a solenoid then there may be a problem there. What current does the ammeter show when you turn on the ignition switch?
 
Building on what crosscut and nkaminar said, the starter is not blowing the fuse because the fuse is not within the starter's circuit. The amps for the starter runs straight from the battery to the post on the starter switch through the starter to ground via the engine block. While the fuse is mounted on the starter and the wire attaches to the post on the starter, the amps the starter draws does not run through that fuse. The fuse is always hot, so if it isn't blowing before you start the car that indicates that there isn't a problem with the fuse holder itself. I suspect that you have a short in your ignition circuit and the fuse actually blows when you switch on the ignition. Places to look: the wiring for the ignition switch may be frayed and shorting against the gas tank, the pigtail connecting the lower plate in the distributor to the points may be frayed and shoring against the distributor.
 
Will N has the straight skinny on the ignition. The power usually connects straight from the terminal box to the coil but the ground circuit runs from the switch down to the distributor breaker set through the lower connection to the condenser. This is if it's stock. Several modifications are common for new type switches and such. Some switch the power and others switch the breaker points like original. A short can happen anywhere but keep in mind that the breaker points are also a switch which only powers up the coil when the points are closed. The circuit is dead after the points open and the condenser peters out. The ammeter is also in the circuit. I've had the dash light short out against the tank and burn up the ammeter so there are possible checks behind the dash as well.
 
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Thanks for all the good information. I am new to the Model A world and it seems like a giant puzzle. BUT,
I think I found the problem. Just before the fuse started blowing, I noticed a head light was burned out. I had pulled the old bulb and ordered a new one. One of the bulb connections in the socket was leaning over and touching the side and shorting out.
I cut a plastic straw into 1 inch pieces and slid over the contacts so they couldn't touch the side and the engine fired up and no more broken fuse.
So, with a 6 volt system, is my 20A fuse heavy enough? A couple guys suggested 30A.
 
As you found out, a short will draw a lot of current. I would continue to use the 20 amp fuse but carry spares and a couple 30 amp ones. A short will blow a 30 amp fuse.
 
This is the first time I have tried to use the Ford Barn site and not sure exactly what I am doing. After posting my question, I couldn't figure out how to get back in and see any replies. Obviously the system works. Just seems a little intimidating at first. I just need to look around and figure it out.
I think I posted a reply that is visible to everyone now.
Thanks for your help.
 
G. Bennett, Welcome to the Barn. When you can post some photos of your car. Also, please add your location to your signature. Have you joined your local Model A club?
 
Self inflicted wounds, it was running before I did this and that, what did I do before now it won’t start, I adjusted the points and put the back together ( without the rotor ) found the rotor setting on the coil where I put it ! LOL happened when working in a dark shed and black parts and pieces seam to disappear !
 
I suspect that the wiring in your car is "not factree" (as Derek Bieri likes to say) In other words, non-standard. The headlight wiring would only be energized so that a fuse could blow if you turned on the headlight switch. Were you turning on the headlights before attempting to start the car? Are your headlights somehow wired into the ignition circuit?
 
G Bennett - When you’ve posted, scroll to the very top. Just below the thick black line, click on “Model A (1928-1931)”. This will show the entire forum again, now including the thread you posted to (or originated).
Click on New Posts within the black bar if you want to see all new posts across all the forums.
 
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