I am a bit concerned about the lack of fusing on the wiring. My thought was to add a fuse to the that wire from the starter switch to the fuse block. What would be the correct amperage for this. Also a fusible link from the battery to starter switch in case the switch grounds out from the insulators failing...Thoughts?
The Model T needs one fuse and it should be a 25 amp in the main load feed yellow from the starter switch as near the switch as possible.
FunProjects makes a neat waterproof fuse kit for this purpose.
The attached wiring diagram will explain further.
In my opinion there is no need for a fuse in the starter circuit.
Ron the Coilman
Fun Projects offers a nice weather-proof fuse holder kit.
More trouble than a water pump.
I have never seen a fused starter circuit on any car.
There is a fuse kit sold for the Model A that goes in the wire after the starter for the lights, ignition etc. I have seen so many give trouble on tours that we sometimes joke about model A drivers not being able to keep up with the T Fords.
The most trouble free way to do it would be to put a fuse in each wire after the junction block.
One in the tail light wire (15 amp), one in the wire to the high beams and one in the low beam wire. Fifteen amps for each should do.
The wire going to the stop light switch would also use one.
In-line fuse holders would probably be best.
Or you could mount a fuse panel right below the junction block.
Now to make it stop better and go faster you get a Chevvy V8 and.......never mind.
Sorry Ron, I didn't see your text above the wiring diagram before I typed out my post.
If I had I would not have commented at all.
I did not know about the Fun Projects fuse.
So if that fuse let's go or burns out or the connection goes bad you burn out the gen.?
Article from back in the day with fuse block for the T.
And the 'kit' sold by FunProjects, using Marine grade parts for waterproof placement when mounted at the 'recommended' spot by John, nearest the hot battery.
This may be the best place electrically speaking, but a pain if you forgot where you spliced in the fuse holder, and you have to get out and get under to fiddle with that 20amp fuse
For me, the easy way is fuse off from the yellow wire on the firewall. For this install wanted a period looking metal fuse holder with wood screw mount, easy to access and looks 1920's
I have traficators that pulls quite some amps, so as the traficator + highbeams + wiper use 35 - 40 amps, I'll need a 50 amps fuse. However, when the engine runs and so the generator, the pull of amps are lower, but the fuse must be able to hold the current if the engine stalls.
A fuse is not a device that you should have to routinely replace. It is a safety device that should ideally never need to have service. All connections in the wiring of a 6V system (or even a 12V system for that matter) can cause intermittent problems and thus I do not advocate the "more is better" idea again when installing a fuse in the T. A single 25 amp fuse placed at the very source of the juice at the starter switch end is the proper place to install the thing and it is easily accessible with the floor board pulled up. It will only blow when there is a catastrophic failure of the wiring system somewhere and when that fuse needs to blow it will NOT make much difference where the fuse is located but if the fuse is located on the firewall then all wiring from the source up to the fuse holder is unprotected. The wiring in the T loom anywhere is heavy enough to blow a 25 amp fuse when there is a short of that wiring to ground. This only assumes that the fuse is the normal fast blow type. The fuse is not there to act as a debugging aid for wiring problems. It is there for safety only and that should then be the only concern when picking a location to install it. It adds 2 connections and yes those can add to the unreliability of the wiring but a single fuse adds safety where there isn't any at all and "More is better" is again misplaced thinking if you then want to add additional fuses that may or may not blow anyway depending on where the short is. The Model T is a very simple electrical system and one can visually check every wire in the car in a matter of a few minutes. If you think you will need to access your fuses constantly then I strongly suggest you rethink the whole thing and think about replacing the wiring totally. A single fuse properly placed is what I strongly suggest you use. I honestly don't care where you buy it but install a good holder with a 25 amp fuse and put it in the source end of the solid yellow #12 wire at the starter switch end of that wire. That is the source of all juice to the small wiring which is the endangered item that can overheat and melt catastrophically if there is no fuse.
Argument free on the need of all T's to have a fuse in the hot wire to the terminal block.
Over the years have experienced 'smoke' from behind the ignition switch twice when running. First one was worn out amp wire, second was direct short to dash with dash lamp wire.
Needless to say, not fun to watch or smell your T's wiring melting away . And risk of fire or destruction when your T is parked in the garage.
Fuse it or Lose it
On the front of the seat a couple inches behind and above the starter switch I have a battery disconnect switch on my '26 touring.
It disconnects the ground cable so everything is dead. It has been that way since 1997.
Not only is it good to disconnect in the garage but it is great for in the event someone accidently heals the starter button, like kids.
Also, If I see smoke I can pull over, reach down and turn the switch.
I am not a fan of disconnect switches since they have been linked to more problems than any hypothetical problems they have solved. I would argue that if you are driving down the road and you see smoke it is already way past the time when the fuse would have blown to save your wiring and shorts are far more likely to happen while you are driving than when your car is sitting in the garage. Most garage fires seem to be linked to battery charging efforts that were not thought out very well. By the time you pull over you might have enough time to jump out of the car and I would most certainly take that exit and leave the car if it is smoking. A disconnect switch is not used on modern cars and modern cars have way more wiring per fuse than does a T with a single fuse. I see this argument a lot in favor of a disconnect switch serving the same purpose as a fuse but they are miles apart in function in my mind. I have made my case for the single fuse idea and now it is up to each to accept or reject the concept. This is for sure a place where your mileage my vary - widely.
While I am not sure about the voltage regulator or diode type cutouts.
If the fuse blows wouldn't it be like the battery is charged and the points open then the current passes through the shunt wire to ground on the mechanical type cutouts.
Mark - On cutout controlled generators, a blown battery feed fuse can lead to a smoking generator. Without a lead attached to the battery the generator will attempt to output its full capacity or die trying. In most cases, it dies leaving a trail of melted solder. This is the reason I don't like the single fuse approach.
If you use a fuse on the battery feed, you should also install a fuse on the generator field to third brush wire. This will save the generator should the battery to generator circuit be interrupted.
I have heard this argument before but I feel it is a flawed argument for 2 reasons.
1) If there is a short to ground and the 25 amp fuse blows then that same short will be shorting the generator to ground too and no harm will happen to the generator since it will have the load of the short on it.
2) In any event that might prove intermittent short - how could the car wiring possibly be better off without a fuse if there is current flowing in the loom that is of a magnitude far greater than the loom can carry without melting. If a 25 amp fuse is there and blows - it is saving the car and the least of my worries is a burned generator which can be rebuilt much cheaper than the whole car and perhaps garage too.
The T is a 20 amp system and typically systems are fused at 125% of their carry current. The 25 amp fuse then should never blow under any normal activity. It is just there to prevent disaster.
I guess I have to agree that if there is no fuse in the car then most certainly there will never be a need to replace it.
Even if it does kill the generator, would you rather spend $200 on a new one, or see your Model T burned up?
I don't see the Model A guys having this discussion and the fuse is in the same main feed line from the battery when installed in a Model A. The Model A has/had the same cutout and 3 brush generator.
The Model A vendors have for a long time carried a fuse kit that installs at the starter switch. It has had some problems of being open to rain and dirt but it still does its job if called upon to blow.
What size fuse is recommended for use with an alternator?
I didn't say I was a proponent of "no fuse". I simply said I don't like the single fuse approach. I like fuses on everything. And it's not $200 for a generator, it's closer to $300. And that's IF you have a usable core. With no core and shipping, you're flirting with $400.
I'm saying spend a buck and save a $400 headache. And spend a few more bucks and save a $14K headache. (Or whatever your T is worth.)
The generator fuse is not there for shorts. It can save the generator should a newbie disconnect the battery feed or mis-wire the circuit. It will save the generator if the circuit is broken for what ever reason. It will also save the generator if one of the battery terminals becomes disconnected or loose. Look how many times a bad battery ground is diagnosed on this forum for starter problems. That same bad ground can destroy a generator.
And to make my position clear, I put fuses on every circuit I can.
Unless you upgrade the ammeter and wiring to much heavier wire the same size fuse of 25 Amps is correct since the fuse size relates to wiring system capability and NOT charging device rating. The problem is that you can pop the 25 amp fuse rather easily with a typical alternator and high RPM.
No, but I've said here before that the fuse and the FP voltage regulator give you an electrical system that is as near to disaster proof in a vintage vehicle as you can get.
So what happens if a tail light or head light wire shorts to ground. I think you'd see a lot of smoke before that 25A fuse blows. Regulator or no regulator.
That's where one's wiring skills then come into question Ken. There's nothing much to be done for lousy wiring. All over the internet you can find photos of Model T's with rats-nest wiring and those cars will be the ones that have trouble. Typical CB'er wiring done up with bits of black tape and white Tywraps is always good for laughs. One of my three Model T's had a nightmare of wiring in it - bare wires twisted together and left that way, ignition switch connections so loose that I had to wonder what was keeping the screws in that last half turn, and this was just inches away from the gas tank. There were also timer wires rubbed thru to bare wire on the crankshaft pulley causing coils to have a much higher duty cycle than intended. There's no end to horror stories but if a person just takes their time to do a job right, with the correct supplies, then there is never a problem. The last Model T I bought got a wiring lobotomy too and I hand wired the entire car from front to back and added turn signal and brake lights. All the lighting is now LED and consumes 1 amp when every light is on. I didn't hesitate to turn on the key and start it up either - and no magic smoke leaked out anywhere. Again, the FP regulator saves the genny when the one main fuses blows for whatever reason, but atleast the fuse saves the car and the regulator saves the genny. That's all you need in any Model T whether it's a plain-Jane T or a sleek racer. Little shorts like an individual light obviously won't pop a large fuse but the short shouldn't have happened in the first place. I have 5 vehicles parked in my garage year around along with stored gasoline and an acetylene cutting outfit ... and I sleep good at night!
You bring up a very important point. How does a large fuse protect light wiring? I will use your example short in the tail light wire. Stock wire size for that run back to the tail light would be #16 AWG but modern repro harness has #14 as the lightest gauge. I will assume #16 and without measuring its actual length I will estimate that since the wheel base is 100" that the wire to the back is about 10 foot long or less and we will assume the short is at the very end somewhere inside the tail light to ground. To quickly blow a fuse you need a large overload and a short as described would result in a theoretical current of well over 150 amps based upon the resistance of #16 wire being .00402 ohms/foot. Thus our 10 foot of wire would have a resistance of .0402 Ohms or so and ohms law says the current would be 6.3V / .0402 = 156 amps which is more than 6 times the rating of the 25 amp fuse. It will blow almost instantly. The wire needs a bit of time to heat up so I doubt you would see any smoke at all. If the wiring harness were the more typical #14 wire then the current would be higher and the fuse would blow even faster. Not all wire gauges would be protected in the car if any of the wire had a resistance high enough to present only a small overload to the fuse. I believe one fuse is enough because the lightest wire used by Ford was #16 AWG and the repro harness is even safer. The fuse is to protect the wire. Of course #16 wire would not be able to carry over 100 amps on a continuous basis but it can carry a very large current long enough to blow the fuse. Reasonable care in keeping all connections tight also helps blow the fuse quickly when trauma occurs.
#14 looks better on the repro harness since it more closely matches the old original harness with its #16 wire because that insulation was very thick and is nearly identical to the #14 modern cloth covered wire with regard to outside diameter.
That above post from John is why most of us read this site. To get information we could find no other place. Thanks for that explanation John.
I also did not know the FP regulator would save the gen.
I now like the idea of a fuse in the main wire much better than I did before.
Since I use a small alternator I still don't intend to use any fuses. I have good wires and good lights that will not cause shorts.
I have a pair of non stock stop/tail lights.
I think I may have a fuse in my directional light system before the flasher though.
I know you are right John but I still don't like the single fuse. If for no other reason, multiple fuses will speed diagnosis of the problem. And I don't lose my headlights and a $300 generator just because the tail light shorts out.
Careening off into the darkness will prove my point.
Oh yes, and shorts are not always constant. A wire falling out of a connector, a chaffed wire bouncing to ground or even a broken socket spring can cause intermittent shorts. The idea that a short that pops the 25A fuse will also maintain ground to the generator is a hopeful thought at best.
In past threads it has been said that sometimes the starter button (or switch - that thing sticking thru the floorboards that we step on with our heel) contacts become "welded" together and the starter continuously runs -OR - that starter switch fails and shorts and smoke (and fire?) ensues.
How does the Fun Projects yellow wire fuse alleviate that problem? Or, is that switch failure the reason some folks advocate installing a solenoid?
Or, is the only solution to always carry a suitable wrench to be able to rapidly disconnect the battery?
Thanks for the answer(s).
I have never personally heard of a Model T starter switch welding its contacts since the contact copper strip inside is not heavy enough to not burn through with a short hooked to it. Hypothetical examples of how wires might intermittently short or not can be dreamed up that will defeat any safety system. The fuse is a time proven common sense safety item but houses have fuses and electrical items still cause house fires usually by lack of common sense. I think this thread is no longer conforming to its titled purpose. Folks should add the fuse or not as they see fit.
"Folks should add the fuse or not as they see fit."