Ignition Switch Wiring

[blown240]

I am trying to understand the correct way to wire in a 2 pole ignition switch with a push button stater switch.  I have been told that you cannot have the ignition switch fused, but I want to use a maxi fuse.  

Why wouldnt #2 work here, and what do you say to #1?

[donsrods]

I guess you want to use a seperate starter button for the "old timiness" flavor, otherwise I can't see any reason to do it. But if you want that, this is ok, I just wanted to understand your reasons for doing it.

I wouldn't do it like any of the 2 drawings. There is no reason to run the power from the ignition switch to the starter button, because you would have to turn the key on first to get power to the starter button, and it would also drain some of the current that should be going to fire the coil.

I would suggest just using a simple ignition switch that has only an on and off position, and get the power for it from the fat terminal of the starter (looks like a chevy setup in your drawing). Out of the ignition switch run your wire to the appropriate resistor to bring the current down to the acceptable 4-7 volts to run the coil.

Then I would take the power for the starter button right off the plus side of that ignition switch and run it to the starter button, and from the starter button right to the small terminal on the right side of the starter solenoid.
Finally, run a wire from the small terminal on the left side of the starter solenoid to the plus side of the coil, to provide a full 12 volts to the coil when cranking.

If you want to use the maxi fuse, go with at least 50 amps, but you don't really need to, unless it makes you sleep better knowing the circuit is protected.

I would have included a drawing, but I am computer stupid, so I can't do that stuff yet.  Hope this helps.

Don

[enjenjo]

Either one will work, number one will put less load on the igniotion switch. A fuseable link works better, particularly of you are using a generator, unless you are running a computer. No reason you can't run two power circuits, one with a Maxifuse, and one with a fuseable link.

[blown240]

Whats the difference between a fusable link and a maxi fuse?

[rooster]

Whats the difference between a fusable link and a maxi fuse?

this may help.
http://www.roddingroundtable.com/forums/viewtopic.php?t=3898&highlight=fusable+link

[enjenjo]

Whats the difference between a fusable link and a maxi fuse?

If a wire is momentarily shorted, if it's protected with a Maxifuse, it will blow, if it's a fuseable link it won't. If the short lasts longer, the fuseable link will blow too.

So for older systems that are not as sensitive, a fueable link is fine. But if there are computers or other electronics involved, a Maxifuse offers better protection.

[PeterR]

Either one will work, number one will put less load on the ignition switch..

Anyone doubting the wisdom of enjenjo's words should pull apart a modern ignition switch.  There are separate contact sets for general ignition circuits, accessories, and starter solenoid. Each of these contacts is more substantial than the wimpy contact set which carries the entire load in an older style on-off ignition switch.

If you have any more than the most basic electrics the relay is worth fitting for reliability.

I would take the power for the starter button right off the plus side of that ignition switch and run it to the starter button, and from the starter button right to the small terminal on the right side of the starter solenoid.

This is the way it was usually done in the past, and it does have one feature that when working on the engine you can crank it over without the engine firing.  But there is a downside.  A friend had a similar arrangement and allowed a young kid to sit in the driver's seat to have a pretend drive.  The keys were not in the car so it was safe, --until the kid pressed the starter button.   The car was a stick shift left in gear and the car leapt forwards sending onlookers jumping out of the way.

Running the feed to the starter button through the ignition switch avoids this risk, but the quite substantial solenoid current has to be carried by the wimpy contacts of the old style ign switch.   Diagram #3 which is a modified version of #1 uses a relay in the engine bay to overcome all these issues.

[blown240]

So in #3 the only load on the ignition switch are the relays, which must be minimal.  That is cool and makes it an easy circuit to put a kill switch or 2 into.  And in that case, they can easily go after the maxi fuse.

[PeterR]

So in #3 the only load on the ignition switch are the relays, which must be minimal.  That is cool and makes it an easy circuit to put a kill switch or 2 into.  And in that case, they can easily go after the maxi fuse.

If the kill switch is an anti-theft device, the best place is in the ground wire to the ignition relay.  Carries a tiny current so the switch can be a small easy to conceal type, and the security wiring is not immediately recognisable.

If the kill switch is a safety switch, there is an additional issue to consider.  Depending on the particular way your alternator is wired, it is possible to have an isolating switch in the main feed turned to OFF but for the alternator to supply power to the ignition and keep the engine running.

[blown240]

its purely an anti theft device.

[blown240]

I think this is what I am going to end up doing.  I know it looks more complex than it needs to be, but it will allow all the functions that i want.

[donsrods]

Not being critical, but why all the relays? I know the purpose of a relay is to allow you to pass a lot of current triggered by a small amount of current, but you aren't dealing with that kind of flow in the typical starting circuit. Push button starter switches can handle this amount of flow on their own, and so can a 2 position ignition switch. Been running mine for 15 years in my '27, and for more years than that in some of my other projects. Boats use this same setup, sans relays, and have no problems.

I just think you are over complicating the situation. Again, not putting down your idea, but I think it could be simpler and less problem prone.

[blown240]

The reason for all the relays is because the kill switches are tiny, and cant take much juice.