Adding a second fuse

B

badbones

Junior Member
Still new here and I have a 29 Tudor that is still 6v with a nu-Rex alternator that was on the car when i bought it.

Sadly this weakened I had to use my AAA card to get home. She completely died on me In a left turn bay. I later found that I have a 15amp fuse on the starter that blew. I am working on tracing the short and have it down to the horn wiring area at the bottom of the steering or the brake lite switch.

While on this topic I found grease in the assembly where the switch is at the wire harness at the base of of the steering column, is this normal to have grease in there? Was wondering if that caused the short.

I am thinking of putting a second fuse on the system to at least allow the vehicle to run if the lighting side blows the fuse. If I add the fuse to the wire that goes from the alternator to the firewall pane, will there be any damage to the alternator or the equipment that goes from the alternator to the harness that attaches to the steering wheel?
 
There may not be anything wrong other than that 15 amp fuse was way too small; most people use a 30 amp on that "starter" fuse block, but you want at least a 20 amp. I'm surprised it didn't blow the first time you stepped on the brakes while you had the headlights on.

There shouldn't be any grease in the switch thingy at the base of the steering column, but commonly steering gear lube leaks down there unless you've got one of those aftermarket tube adaptations that isolate the gear oil from the switch rod. Since grease is a poor conductor, it's probably not the cause of the short.

There have been other threads on how best to add fuses--try search, if just adding a bigger fuse doesn't work.

Steve
 
The car was actually running great on the 15 amp fuse since I bought her. I did read most go to 30 and I planned on that and to ad a second that was 15 or 20amp for just the lighting side of the system. Also I did order a new stop switch since that seemed to be the one thing i was doing when the car died as I came to a stop
 
Last edited:
There is probably nothing wrong with the stoplight switch other than it works--more current is supposed to flow when you step on the brakes. That, together with the current going to the ignition circuit might put you over the 15 A limit and blow the fuse. You could drive all day long on the 15 A fuse as long as you don't step on the brakes, turn on the lights, or blow the horn.

If you add a second fuse for the lighting circuit, you're still going to need a bigger fuse on the starter: all of the current used by everything (except the starter) goes through that unit.

Steve
 
Speaking of fuses, I use the Bussmann CBF Circuit Breaker in 30A that replaces the glass tube type fuse (saves on buying fuses). I have a 12V system in my A and would like to use this in my other driver that is still 6V. As of now I'm using the glass tube because I'm unable to locate a CBF circuit breaker in 6V 30A. If they don't make it in a 6V version what would be he negatives to using the 12V 30A? It opens when it detects a short and closes when the short is no longer present. What does the voltage rating protect? I hope I'm not embarrassed when I find out the answer.
 
Steve. The car drives perfect on the 15amp surprisingly at night with no prob so I guess I was lucky

What is the best place to put a second and smaller fuse tan the starter fuse.?

Would it be on the alternator to the firewall or the alternator to the steering wire harness?
 
Last edited:
A 12volt 30 amp fuse will work just fine at 6 volt. This type of breaker works by heat caused by current flow (it is called a thermo breaker, when it gets to hot it opens, when it cools down it closes). It may not open right at 30 amps, however I would bet it does not at 12volts either.
 
badbones said:
Steve. The car drives perfect on the 15amp surprisingly at night with no prob so I guess I was lucky

What is the best place to put a second and smaller fuse tan the starter fuse.?

Would it be on the alternator to the firewall or the alternator to the steering wire harness?
Click to expand...

Be careful do not fuse the alternator output wire, it needs to stay connected to the battery. If it looses the battery load the voltage can go high and burn out the regulator or the alternator, or both, it may not happen all the time but it will happen and then you will have bigger problems. One way to keep power to the motor is to unhook the wire that feeds power to the coil and run a new wire with an in line fuse holder and fuse from the coil to the unfused side of the fuse plate you already have on the starter.
 
Jon

So are u saying to put it to the wire that goes from the alternator to the wire harness at the steering wheel? This way if it blows there I will still have a 30 amp on the starter to support the ignition system? What size would be good to put on the alt...a 15 or 20? Since it should be less than the main fuse on the starter
 
Regardless of whether the car drives fine with a 15A fuse you most likley need larger.
If you look at any fuses specs, it will indiate how long it will take to blow at any given current typically listed in hours or hundreds of hours. For example a 15A fuse will probably blow over time if you constantly draw 13A through it. 14A will cause it to blow sooner, and 15A will be very fast.
 
foxfire42 said:
Speaking of fuses, I use the Bussmann CBF Circuit Breaker in 30A that replaces the glass tube type fuse (saves on buying fuses). I have a 12V system in my A and would like to use this in my other driver that is still 6V. As of now I'm using the glass tube because I'm unable to locate a CBF circuit breaker in 6V 30A. If they don't make it in a 6V version what would be he negatives to using the 12V 30A? It opens when it detects a short and closes when the short is no longer present. What does the voltage rating protect? I hope I'm not embarrassed when I find out the answer.
Click to expand...
Foxfire,
I use 12 volt G.M. blade type circuit breakers on 6 volt systems and they work fine. The breaker is DUMB, and doesn't know it's on a 6 volt system, shhh, don't tell it. It's excess amperage flow that opens it, not voltage.--Bill
Don't be embarrased, if we are embarrased, it just gives us a good glow and folks will say, "You look GOOD, you have such a healthy glow."
 
Last edited:
I have looked several times over in the Restoration Guidelines, J/S Area #2 & I cant find anything on FUSES or CIRCUIT BREAKERS in a Model A Electrical System ??.
 
badbones said:
Jon

So are u saying to put it to the wire that goes from the alternator to the wire harness at the steering wheel? This way if it blows there I will still have a 30 amp on the starter to support the ignition system? What size would be good to put on the alt...a 15 or 20? Since it should be less than the main fuse on the starter
Click to expand...

Yes, that is a good place to put a fuse. It will protect the supply to all your lights without killing the ignition if it blows, and will leave the alternator connected to the battery if it blows. I would try a 20 amp and if that blows, go to 30. True direct shorts (wire rubs through insulation to ground, that sort of thing) will sure blow a 20 or a 30.
 
badbones said:
Jon

So are u saying to put it to the wire that goes from the alternator to the wire harness at the steering wheel? This way if it blows there I will still have a 30 amp on the starter to support the ignition system? What size would be good to put on the alt...a 15 or 20? Since it should be less than the main fuse on the starter
Click to expand...

No, do not put it in that wire, if the fuse blows it would be hard on the alternator.
The only change you would need to make to accomplish what you want is to unhook the wire on the - or neg side of the coil and tape it off or remove it. Then take a new wire that has an in line fuse of about 10 amps and run it from the - or neg side of the coil to the unfused side of the fuse you already have on the starter, or just hook it to the bolt that the battery cable hooks to on the starter.

And no this is not any way close to "orginal" wireing, there were not any fuses that I know of orginaly. All fuses are a after thought to reduce the risk of fires and burned wires.
 
badbones said:
Steve. The car drives perfect on the 15amp surprisingly at night with no prob so I guess I was lucky

What is the best place to put a second and smaller fuse tan the starter fuse.?

Would it be on the alternator to the firewall or the alternator to the steering wire harness?
Click to expand...

IMO, it should be on the alternator to steering wire harness, close to the alternator, the yellow with black tracer in the diagram. Actually, I think a short is more likely in the horn circuit, which suggests a fuse also in the yellow wire from alternator to steering wire harness.

I think Jon's idea of a separate hot wire to the coil is probably the best (only) way for isolating the ignition circuit so the car will keep running when the big fuse blows. The only problem with it is that it puts the ignition circuit in parallel, rather than in series, with the ammeter; that means the ignition current won't register on the ammeter and you lose the ammeter's utility for diagnosing ignition issues. That's a high price to pay, in my opinion. Also, in that regard, notice that the wiring diagram below is for the earliest arrangement that also isolated the ignition circuit from the ammeter; the improved practice had the black coil wire going to the other terminal box lug.

Steve


ModelAwiringdiagram-FloydClymer.jpg
 
Last edited:
Leave the fuse in place on the starter, but change to a 30 amp fuse. Add a 20 amp fuse between the alternator output terminal and light wire going into the bottom of the steering column. Now, the lights can short and blow a fuse, but the coil will still spark and the alternator will still charge the battery.
 
You must log in or register to reply here.
Back
Top