How much Amperage/voltage goes through the master switch?

[TehTDK]

Fellow SS'ers

I am in the process of looking for a way to "lock down" the master switch. Lock down in such a way that no matter if you switch it on or off nothing electrical gets powered on, until the keyswitch I am going to install is turned to the right position.

ie like this
Master Switch on, Key off - No power
Master Switch on, Key On - Power
Master Switch Off, Key On- No Power

Simply wiring a keyswitch before the master switch is the solution I have come up with so far. My problem however consists of making sure I actually get a keyswitch that can sustain the voltage/amperage that normally goes through the master switch. As far as I understand, the M35 etc can't start without the master switch on, which at least to my conclusion means that the cranking current actually passes through the master switch. And so far I haven't been able to find a key-switch that can withstand that kind of amperage.

Unless all the master switch does, is to effectively trip a relay that then handles the voltage/amperage that goes through the truck and thus doesn't pass the load through the switch?.

But I apologise in advance if the TM actually mentions this and provides charts that detail it. But I figured those parts were only covered by a wiring diagram, which I would have to admit I am not an expert at reading at all.

But thanks in advance for any help or direction I can get in regards to this.

 

[Cleveland Iron]

The accessory switch itself is just a big heavy switch; no relays to complicate things. When you hit the starter button you are actually energizing a relay that powers the starter moter. If I were you, I'd get a cheap amp meter ( 5 or 10 amp on the high range. ) and see how much the relay coil draws when you hit the button. It should not be more than a few amps. The standard truck wiring should not allow more than that sort of draw even for a short time.

Unless I am complletely crazy, you should be able to pull power off of the accessory switch. If you are worried, about putting that load directly on the accessory switch, just get a hefty 24V relay from an electronics surplus store. Wire the contacts in line with the start switch and power the relay with the accessory switch. The good part here is if you add any other things than use a 24V load, you can wire them in off of the relay ( assuming it is heavy enough ).

I hope that helps.

 

[TehTDK]

Well I plan on getting away with the starter button and implimenting a regular keyed ignition switch. But that ignition switch still relies on the Master switch being turned on, otherwise the engine wont crank since it has no power. So i planned of adding an locked "master switch" as an additional layer, ie a switch that basically breaks and connects the master switch. But in order for that to work I would need to know how much current etc that is actually running through the master switch once its turned on, as the switch I would be getting would need to be able to carry that load.

But that the cranking amperage and current is NOT carried over that switch at least simplifies the task somewhat. The company I talked to said the biggest they could do for switches was one that could take 10 Amps, but I suspect that might be a bit much for this setup?

 

[patracy]

Just a SWAG here...

Lights = 5 amps (28v at 140w)
Signals = 3.6 amps (28v at 100w)
Dash lights = 3.6 amps (28v at 100w)
Fuel pump = 6amps

So if you have a heater it will be higher, but you're at 20 amps barebones.

 

[Cleveland Iron]

I try to err on the parinoid side of things... When I installed my 12v system, I used a set of relays to isolate things. Got them from a local ( Cleveland, Oh ) place called Electronics Surplus. They work just fine. Sorry, no part numbers for you though.

 

[Cookie]

What I plan on doing is adding a remote controlled relay placed out of sight. Same thought as you except even with a keyed ignition switch unless it is sealed all they need to do to bypass it is short across the terminals. Different story if the security switch is hidden. Just a thought.

Here are systems made for the purpose http://www.autozone.com/autozone/ac...268t?filterByKeyWord=remote&fromString=search

 

[Cleveland Iron]

Just remember that stuff appears to be 12v...

 

[SCSG-G4]

My master power switch on the deuce has two sets of wires which bring power in and have it flow out, so each one is only handling half of the power that needs to flow through. Pretty much everything else is handled by relays. If you want a real master kill switch, you need something that isolates the negative lead from the batteries (IE, cable runs from rear battery neg post to kill switch, then from kill switch to frame ground). Something like a 'sea-dog' heavy duty on/off switch with key (500 amp), part no 420600-1. When it's off, nothing works!

 

[Cookie]

Pull power from one battery for the relay coil and it works fine. Relay contacts are isolated from the coil.

I use one of those big red square boat switches under the hood for the stereo on my paintball tank.

 

[steelandcanvas]

A keyed battery cut-off switch in my opinion is the best option. A keyed ignition switch is still real vulnerable to jumping the terminals, and getting the vehicle started. Most people would think the batteries are dead when they turn the ignition switch on, push the start button and nothing happens.

 

[TehTDK]

I called up my local electronics supply and the only keyed on/off switches they could supply was 10Amps at best. It just seems far fetched that something as "old" as the original master switch would actually be able to handle 20 amps of sustained drain going through it without burning out. But reading your various comments I can see that my plans are not as easy as I had initially considered.

I had hoped I would be able to wire in the keyed Switch either before or after the master switch. But if 20+ amps of power is running through the master switch then I will be stuck at a dead-end right there. My planned setup looks more and more doomed from the start :/

A keyed battery cut-off switch in my opinion is the best option. A keyed ignition switch is still real vulnerable to jumping the terminals, and getting the vehicle started. Most people would think the batteries are dead when they turn the ignition switch on, push the start button and nothing happens.

But wouldn't a battery kill-switch be subject to the same amperage values as any other switch. I mean if the switch is open it would have to sustain the amps that is drawn on cranking as well as on regular running, which I would suspect is a lot. But then again if you have a heavy duty marine cut-off then perhaps. It just seems like most regular off the shelf items wont actually be able to stand up to the electrics of the vehicle.

And the keyed ignition switch I plan on making will be encased in a box and screwed to the dash from the inside and then insulated etc so that it is actually waterproof or as close to it as it can get in case I want to take the truck for a swim. Electronics and water are rarely a good mix . But other then that your point is very valid, but as someone pointed out "Locks keeps honest people honest". If someone wanted to steal one of our trucks then they would not stop.

 

[steelandcanvas]

I called up my local electronics supply and the only keyed on/off switches they could supply was 10Amps at best. It just seems far fetched that something as "old" as the original master switch would actually be able to handle 20 amps of sustained drain going through it without burning out. But reading your various comments I can see that my plans are not as easy as I had initially considered.

I had hoped I would be able to wire in the keyed Switch either before or after the master switch. But if 20+ amps of power is running through the master switch then I will be stuck at a dead-end right there. My planned setup looks more and more doomed from the start :/



But wouldn't a battery kill-switch be subject to the same amperage values as any other switch. I mean if the switch is open it would have to sustain the amps that is drawn on cranking as well as on regular running, which I would suspect is a lot. But then again if you have a heavy duty marine cut-off then perhaps. It just seems like most regular off the shelf items wont actually be able to stand up to the electrics of the vehicle.

And the keyed ignition switch I plan on making will be encased in a box and screwed to the dash from the inside and then insulated etc so that it is actually waterproof or as close to it as it can get in case I want to take the truck for a swim. Electronics and water are rarely a good mix . But other then that your point is very valid, but as someone pointed out "Locks keeps honest people honest". If someone wanted to steal one of our trucks then they would not stop.

They are several manufacturers of high amperage cut-off switches. I just looked at a site a few weeks ago with a selection of very nice switches, but I'll be danged if I can remember the site now. If you are still set on the keyed ignition switch, you should have that switch actuate a relay to switch on/off the other loads. The relay will draw a negligable amount of current through the key switch. I think the only loads you'd be switching are the lift pump in the tank, the gauges, and the starter motor relay. I think Drew has already listed the current draw for the lift pump in a previous post on this thread. Get out your handy-dandy clamp-on and figure what the other items draw, I would then get a relay that is rated at least twice this number. The lighting does not go through the ignition/master switch, so there is no need to figure it in. Just my . Hope this clears things up for you.

 

[VPed]

Cole Hersee (sp??) has a variety of keyed switches, some capable of 1000 amps intermittently (cranking). Those switches are usually available at truck and auto parts stores. BTW, if you by a general purpose ignition switch intended for the cars from the 50's and 60's, they will most probably be able to handle the master switch loads including the cranking solenoid. Those systems are 12 volts (and 6 volts) so the amperage at 24 volts is less. (half of amps at 12V and 1/4 of the amps at 6V)

 

[TehTDK]

They are several manufacturers of high amperage cut-off switches. I just looked at a site a few weeks ago with a selection of very nice switches, but I'll be danged if I can remember the site now. If you are still set on the keyed ignition switch, you should have that switch actuate a relay to switch on/off the other loads. The relay will draw a negligable amount of current through the key switch. I think the only loads you'd be switching are the lift pump in the tank, the gauges, and the starter motor relay. I think Drew has already listed the current draw for the lift pump in a previous post on this thread. Get out your handy-dandy clamp-on and figure what the other items draw, I would then get a relay that is rated at least twice this number. The lighting does not go through the ignition/master switch, so there is no need to figure it in. Just my . Hope this clears things up for you.

I thought the master switch determined whether there was ANY or NO electrical current going through the vehicle, ie with the master switch off, you wouldn't even be able to turn on the lights etc.

But from what I can read it seems like the present push start button, actually activates a relay for the starter motor, so I simply has to rewire that to the "springloaded" position on the ignition. Ie me pushing the key to its stop and against the spring equals pushing the start button. Once the truck stops I let go of the key and it flips back, which again is simular to me letting go of the starter button. Now i just need to figure the rest of it out .

 

[Cleveland Iron]

If you are worried about water and electrical... Check the marine alternative. Most power boats use a keyed ignition switch similar to an automobile.

 

[DieselBob]

I looked up the NSN for the master switch (SWITCH,ROTARY) and the spec's for the contact volt and amps are.

CONTACT VOLTAGE RATING IN VOLTS: 28.0 DC AT SEA LEVEL

CONTACT LOAD CURRENT RATING: 10.0 AMPERES RESISTIVE LOAD DC AT SEA LEVEL AND 10.0 AMPERES INDUCTIVE LOAD DC AT SEA LEVEL AND 5.0 AMPERES LAMP LOAD DC AT SEA LEVEL

 

[steelandcanvas]

I looked up the NSN for the master switch (SWITCH,ROTARY) and the spec's for the contact volt and amps are.CONTACT VOLTAGE RATING IN VOLTS: 28.0 DC AT SEA LEVELCONTACT LOAD CURRENT RATING: 10.0 AMPERES RESISTIVE LOAD DC AT SEA LEVEL AND 10.0 AMPERES INDUCTIVE LOAD DC AT SEA LEVEL AND 5.0 AMPERES LAMP LOAD DC AT SEA LEVEL

As Drew pointed out, the in tank lift-pump pulls 6 amps, that leaves you with gauges, (small draw), and the starter solenoid. 6 amps plus the headroom required of the solenoid, you'll be right at or possibly over your 10 amp maximum. Best to use the relay and avoid headaches down the road. Nice specification find BoB!

 

[TehTDK]

So judging on BoB's find a 10 amp keyed switch wired in either before or after the master switch should be sufficient. Or is there something I am forgetting?. Or does the master switch actually "take" 25 Amps ?. But in either case it seems like a switch from Cole H might be a cause of better action, I just wish those switches could be a tad more secure, because some of the 10 Amp switches I have looked at here actually comes prepared for KABA high security locks, even if that might be a bit overkill for a simple "power kill" on/off switch

 

[jatonka]

I have 1000 amp Cole Hersee master switches that are keyed. They get installed in the neg side of the battery system and kill the whole truck. PM me when you want, JT

 

[steelandcanvas]

The switch Bob showed the specs for is a single throw, double pole. I would assume both poles will handle 10 amps each. If you use the keyswitch, you most likely will still need a double pole relay. Put the current at the relay, not at the keyswitch, let the keyswitch control the relay. The keyswitch wired either before or after the master switch makes no difference, the result will be the same.