Okay. So I have heard several reports that a simple master disconnect switch taking the battery out of the loop may allow the alternator to keep running and may send a spike to the engine PCM, possibly frying it.

Here is what is recommended by Johnny Lightning in a previous post:

1. Run a # 1 cable from the ON side of the switch up to the original battery cable that hooks to the solenoid on the fire wall.
2. Unhook the alternator cable from the solenoid on the fire wall and hook to a #2 wire and ran it back to the battery side of the switch.
3. Take a #1 wire and run from the battery positive side to the battery side of the switch same side as the alternator wire.
4. Run a #2 wire from the negative side of the battery to a good ground on the frame (make sure you clean the paint etc. away before connecting the ground to the frame!)
5. Up front I just cleaned a spot on the frame of the truck and I connected the ground wire to the frame. Keep in mind I didn't cut ANY factory wires because I might want to put it back to stock again one day.

Does this sound like it would do it?

Thanks,

 

thats how i've had mine wired for 2 years now. no problem i would recomend a nice 600 amp flexible welding wire i beleive 2-0 gauge will be fine and i also recomend a nice heavy duty fuse like you would buy from a stereo shop

 

Have you actually used the disconnect switch to cut off the truck? Sounds like a silly question, but one that needs to be asked. Thanks for the reply.

 

I would much rather see it take power away form the eec relay than the alt.After all when ever there are contacts involve you get a spark and thats more than 12 volt.Maybe I am being overly cautious but it only takes one to ruin a Computer.Stan

 

HI!... Here's my set-up.

https://www.f150online.com/galleries...4-793-7156.jpg
https://www.f150online.com/galleries...-793-29800.jpg
https://www.f150online.com/galleries...4-793-6941.jpg
https://www.f150online.com/galleries...4-793-6940.jpg

 

Nice setup, Neal, and a great truck. That is one *ss-hauling NA engine!

Just don't tell anyone you relocated the battery--NHRA rules require a master disconnect on the rear exterior of the vehicle.

 

Johnnys explaination is a little hard to understand, so I might be wrong here, but I tried drawing out a shcematic of what he wrote several times, and it seems to me that the alt wire is staying attached to the cable coming off the + battery, so I would think that would defeat the purpose of the switch?

When I did the kill on Spiros truck, I ran a 00 gauge cable from the batt to the switch, then from the switch back up to the solenoid, and did the same with a 2 gauge cable from the alt to the switch, then from the switch back up.

I like Stans idea about the EEC relay, but technically that's not HNRA legal. The cut off switch must kill ALL vehicle power, not just kill the motor. This way there is no chance of fire in the event of a crash. And you have to disable it on the positive side, no ground kill allowed.

 

I think JL was saying to run the positive input current side of the switch to both the battery and the alternator output. Then, run the positive output current back up to the solenoid. Only three positive connections plus a ground.

Below is the diagram that came with the Moroso switch I bought. Does it make sense? Note that the alternator side of the switch is oonly rated at 20 amps. How can this be? Isn't the output current of an alternator way more than that?

 

HI!... Tim : I know ALL about the NHRA rules on a battery relocation set-up. I'm not new to dragracing. I also own a 713H.P N/A "83" PRO STREET RANGER. The reason I did'nt mount my master cut off switch at the rear of my truck is for obvious reasons. I did'nt want any kids to walk by and shut the truck off.I have buddies that have mounted their's back there and people are constantly shutting them off. I only go to the dragastrip about 4 times a years so this was a better system for me. This truck is my daily driver.

 

Don't the NHRA rules say that you have to put the kill switch in a area on the back of the vehicle thats easy to spot?

And you have to do that anytime you put the battery anywhere else then the stock location.

This is a little extreme but I wired mine the way its supposed with the kill switch killing the entire truck.

 

yes i have been asked to kill the truck by a nmra tech inspector and it works very well. i originally wired it to disconnect the negative side but motor still ran as the alt. was still in the loop.

 

NHRA rules strictly specify:

"Mandatory when battery is relocated, or as outlined in Class Requirements. An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The external control switch for this cutoff switch will be clearly indicated by a red flash inside a white-edged blue triangle with a base of at least 12 cm (see drawing 25). The positions must be clearly indicated with the word "OFF". If switch is "push/pull" type, push must be the action for shutting off the electrical system, pull to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch (3.2 mm) diameter. Plastic or keyed switches prohibited."

Our trucks fall under the ET Bracket classes, section 1A in the rulebook and state this:

"Mandatory on any car with a battery running 9.99 (*6.39) or quicker, or any car exceeding 135 mph (217.2 km/h) or on any car where the battery is relocated into the trunk area."

I have seen many times tech inspectors ask vehicle owners to operate the cut off to make sure it's functioning properly. If you don't want a cut off switch sticking out the back of you truck for daily use, then either take the **** off when not at the track, or make a cover panel to hide it for street use. If you are not going to put it in the proper place, there is no reason to even have one. The reason the rules make you put it at the rearmost point of the vehicle, is so in the event of a crash, the safety crew knows exactly where it is. If you have your cut off switch anywhere else, when you crash and die because an electrical short made your car burst into flames because the safety crew couldn't find your cut off switch, don't go bitching to God when you get to heaven.

 

Sal how about running power form the switched side of the disconnect to the B+ side of the ecc relay and run the regular battery power thru the swich also That way when you turn the switch off you lose all battery power and since the ecc relay is getting power off the switched side it would kill the motor.They make special main disconnects for alt vehicles and you could substitute the alt wire for the ecc wire.I think it would work.Also do you have to switch power off or can you switch the ground off?Stan

 

That's not a bad idea Stan. What we really need to determine, is where the alternator is back feeding voltage to, that's keeping power to keep the truck running. I'll check the schematics and see if I can find it. It's got to be feeding voltage to a circuit that keeps the EEC powered. You have to kill positive power via the cut off switch, ground kill is not allowed.

 

I plan on putting a kill switch on my truck and am planning on doing that way but wioll be about after the 1st of the yr.I know they make that type of cut off switch I have seen them but have not ordered any yet .Stan