how to wire master disconnect?

dlampe · #1 (**permalink**) 03-29-2009, 07:32 AM

How do I wire dual master disconnect switches? I want one in the car and one outside. I need to cut the alt. and the battery from either switch. Can anyone give me some insight as to whether this is possible? I have been thinking about this all day and I just can't get it sorted out.

EDIT

Actually, if I cut the the main fuse box power wire that runs to the starter selinoid, the car should shut done even if the alt. and battery wire are still at 12v., right? If so, how do I kill it with dual switches?

vector1 · #2 (**permalink**) 03-29-2009, 08:26 AM

i can't solve your problem, me being electrically challenged anyway, but i ran the alt. pwr lead directly to the battery with 150 amp fuse, 130 amp alt., no need to switch it, the fuse is placed close to the battery (preferred) in the trunk and is always hot for the datalogger unless i disconnect the fuse. the battery also acts as a sink for the alt. juice when you shut things down, no reverse spike sort of thing.

then ran pwr lead forward off battery through master disconnect and on to the pwr grid. you could put two masters in tandem and reach your goal i believe.

if you're doing any type efi be careful!

hth

vettestr · #3 (**permalink**) 03-29-2009, 09:19 AM

Hi,
You mention a dual disconnect but I might suggest you just need to install a diode on the alt. wire to collapse the field and then remove battery supply via the single disconnect.

Avoid the 5 dollar switch from places like Harbor Freight as they are a bit too cheap for this application. A disconnect switch needs to handle some serious amperage and you do not want it to install high resistance in the battery feed nor do you want it to stick or hang closed in an emergency situation.

Break the Positive cable although many will suggest the ground side. The positive side switched allows everything to remain grounded even in our fiberglass cars and they way most are wired. Use the diode as described very well on the MSD web sight under - when installing MSD ignition. with 1 wire alt. use. PS..... quality switches are avail from Jegs, Summit and so on. NHRA approved is the seal to look for or their amp ratings anyway. Have Fun !!!! No big deal and only a 2 adult beverage kinda job

dlampe · #4 (**permalink**) 03-29-2009, 12:20 PM

I don't know what a diode does or what it is. Also, I do have EFI so what are my concerns?

http://store.summitracing.com/partde...5&autoview=sku

Wouldn't this solve my problems if I used 2 toggles?

vector1 · #5 (**permalink**) 03-29-2009, 12:32 PM

Quote:

Originally Posted by dlampe

I don't know what a diode does or what it is. Also, I do have EFI so what are my concerns?

http://store.summitracing.com/partde...5&autoview=sku

Wouldn't this solve my problems if I used 2 toggles?

i had to reroute some wires away from rfi sources, don't mix efi stuff with other power sources would be my advice.

Calbullet · #6 (**permalink**) 03-29-2009, 12:53 PM

I don't know if this helps, but I would just wire them in series. that way you can shut down from within the car, or if tracking, a course worker needing to shut you down, they can do it from the outside. they would both have to be on to work, but if one is off , the system is off.

Mel

vettestr · #7 (**permalink**) 03-29-2009, 03:19 PM

Dean,
I think I know the answers too these ?'s but why guess. What are you trying to do exactly, why are you installing this disconnect and do you care if it meets specific Race sanction rules?

A diode is an electronic device that is a 1 way valve, it only lets current flow in 1 direction. If you put it on the wire from the alternator it stops them funny electrons from swinging both ways. It stops current flow from feeding back and keeping our engine running on the alt. even though the battery was turned off. a 3 dollar item.

Some electronic fuel injections require a battery source to keep their memory stored or some info that the need remember fuel maps and so on. Most systems have ability to remember things without a battery but do need a battery supply to run.

Some sanctioning bodies require a mechanical switch and will not allow electronic or electric battery disconnect switches. (if you wrecked and an electrical fire was starting will the electric disconnect sw still work ?) A mechanical disconnect must be mounted in an exact location so track workers know where to look and how to turn everything off.

Will the Painless Sw. you listed work to stop battery flow .... YEP , but not sure about other questions I asked. Jeff C

dlampe · #8 (**permalink**) 03-29-2009, 04:53 PM

Thanks a lot Jeff. That helps. I will not be running at any type of sanctioned event, just open track, Shelby events and other "fun" days. I'm just trying to be as safe as I can and I couldn't come up with a way to wire the dual mechanical switches.

I have the main battery wire, the alt. wire, the EFI main power wire, and the main power wire to the dash/fuse box. I have 2 mechanical switches in series. How do I make this work? If it goes from battery to switch, switch to switch, then switch to solenoid where the EFI and Dash power connect, where does the alt wire go? Where the battery connects to the first switch?

I realize this is confusing but don't give up on me yet. I'm trying to follow along.

vector1 · #9 (**permalink**) 03-29-2009, 05:15 PM

i would run the efi main pwr and neg. wire directly to the batt. (isolated), efi should have internal fuse, there should be a seperate trigger wire to ignition, i also isolated the ignition to a dash switch that i use to turn the engine off, nice if you want to keep the efi powered up for datalog, etc.;

the alt. charge wire directly to the batt., plumb appropriate amp. fuse into this wire; if there is an exciter you can switch this at dash or plumb hot.

the other hot wires that pwr acc., dash, lights, etc could go through your switches.

you do not want to run your efi pwr off the solenoid terminal or ground to a bus with other electrical items, very important. your efi could be different but they will pick up rfi. mine is the accel unit and it did work fine the way i had previously installed it but it was picking up rfi and displaying trouble codes and lights, not all efi systems will display codes so you could never know if there is a problem.

your msd or ignition amplifier should also be wired both + and - to battery away from all efi.

vettestr · #10 (**permalink**) 03-29-2009, 06:19 PM

OK....
If you simply want a master battery disconnect switch the one you listed from Summit will work fine. Look at their PDF file on the link you included to see how easy to install.

There are many ways to skin a cat and just as many ways to wire your car. All the talk about the alt. is because some will keep running when the key is turned off. If this is not happening and/or reason for the battery disconnect we can move on. You are not trying to solve any issues or comply with some track rules and everything is working so again life is good.

All you want is ability to remove battery from system as safety and a convenience thing, right? If you buy the remote sw. from Summit here is how to install. Remove ground cable from battery - this is to kill everything so you can work on it safely. Remove battery cable from battery side at the starter solenoid and place on NEW DEVICE (voltage in lug). Install a new (high quality) battery cable from NEW DEVICE on the other lug and place other end on Starter Solenoid (this is where you removed the cable from moments ago). The kit shows a toggle on/off switch that comes with the kit I think, mount the switch where you want and run wires as shown in PDF. You should be done after putting Negative cable back on and testing everything.

Other things can be added or removed from the circuit but this is the BASIC install and
SHOULD remove power to everything if wired like I think. You could place the NEW DEVICE right at the battery if you need to because it is a remote controlled device. Any more questions give me a call.
Jeff C 602 402 8504