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I planned on running a single big positive battery cable to the front (probably 1/0), into distribution block, then out to my alternator and starter from there.
A lot of diagrams I see floating around, people run a separate dedicated alternator cable back to the cutoff switch post...I dont see the logic in this? Seems like a waste of cable...
It's not at all. If you're running a cutoff switch it'll be necessary as the alternator will back feed the system instead of killing power. I use 4 post style kill switches. Positive battery terminal to one post with a jumper to the post next to it, then one 4GA direct to the alternator on the third post, then the last post to send a 2GA wire to the starter (I used 1/0 but it's total overkill). Then run a 4GA from the starter lug to the distribution block. Some say to use a 2 post and run the alternator wire straight to the battery, but I don't like leaving a long run of hot wire running under the car in case of a wreck.
Last edited by 93Z2871805; May 6, 2016 at 02:57 PM.
It seems to me, based on NHRA rules for battery location, that the alternator wire should be on the opposite side of the switch. So battery on one side, switch, alternator on other, so when you switch power off, you cut EVERYTHING off AT the battery. If that was the case, then why connect the alternator wire at the back? Or are you saying to connect the alternator wire on the battery side of the switch? If so then I dont think that satisfies NHRA rules.
It seems to me, based on NHRA rules for battery location, that the alternator wire should be on the opposite side of the switch. So battery on one side, switch, alternator on other, so when you switch power off, you cut EVERYTHING off AT the battery. If that was the case, then why connect the alternator wire at the back? Or are you saying to connect the alternator wire on the battery side of the switch? If so then I dont think that satisfies NHRA rules.
Let's say you have 4 posts, 2 are on the hot side, 2 are not. The 2 that are not get the wire to the starter and the wire to the alternator. The power flows through the switch like a cross, so 180* from the battery positive input, you'll have the "to starter" output. However, since you only have one positive input, you jump a wire to the empty post to give the post 180* from the "to alternator" post juice. When you hit the switch, it breaks contact from the alternator and the wire running to the starter and kills everything in the car. Using a 2 post kill switch would mean that you have one post that gets the battery positive and the other gets the wire running to the starter, with that setup you have 2 places to put the alternator wire 1) directly to the battery so it doesn't flow through the switch when broken (this wire will remain hot even when power is cut but will not feed the system, it is NHRA legal, but ill advised), or 2) to the same post that the starter wire is on which will keep the car running even once the switch is tripped and doesn't do anything(not NHRA legal or functional).
Let's say you have 4 posts, 2 are on the hot side, 2 are not. The 2 that are not get the wire to the starter and the wire to the alternator. The power flows through the switch like a cross, so 180* from the battery positive input, you'll have the "to starter" output. However, since you only have one positive input, you jump a wire to the empty post to give the post 180* from the "to alternator" post juice. When you hit the switch, it breaks contact from the alternator and the wire running to the starter and kills everything in the car. Using a 2 post kill switch would mean that you have one post that gets the battery positive and the other gets the wire running to the starter, with that setup you have 2 places to put the alternator wire 1) directly to the battery so it doesn't flow through the switch when broken (this wire will remain hot even when power is cut but will not feed the system, it is NHRA legal, but ill advised), or 2) to the same post that the starter wire is on which will keep the car running even once the switch is tripped and doesn't do anything(not NHRA legal or functional).
Running a two pole with battery and alt (4g) on the same side of the switch and main power and starter on the other side (1/0g) of the switch works. If you do this, which is my plan, it is advisable that you also install a circuit breaker between the battery and alt near the switch. Primary purpose of the switch is to kill the systems in the car, ignition, fuel pump, nitrous if equipped, etc. Secondary is to kill electrical fires. With the battery and alt all on the same non-switched side, there's no way to stop current between them. However, with a circuit breaker, it's an automated process....
Running a two pole with battery and alt (4g) on the same side of the switch and main power and starter on the other side (1/0g) of the switch works. If you do this, which is my plan, it is advisable that you also install a circuit breaker between the battery and alt near the switch. Primary purpose of the switch is to kill the systems in the car, ignition, fuel pump, nitrous if equipped, etc. Secondary is to kill electrical fires. With the battery and alt all on the same non-switched side, there's no way to stop current between them. However, with a circuit breaker, it's an automated process....
Or you can run a 4 pole and it totally kills everything with nothing else added. With a 2 pole switch that entire length of 4GA running to the alternator would still be hot. On a 4 pole kill switch the only thing left hot is the 12" or so of cable from the battery to the switch. My thinking is that I would want everything electrical in the car dead, so if I'm upside down and unconscious in a mangled wreck, I'm not worried about the 4GA wire sparking off of the chassis near a fuel spill before the safety safari can pull me out. Albeit, the circuit breaker would work once it shorts for the first time.
Last edited by 93Z2871805; May 8, 2016 at 09:21 AM.
Thanks i understand the reasoning for putting the alternator on the battery side of the switch so that main power is cut in the even that the switch is turned off.
I am still not following the 4 post switch theory. Internally the switch is the same as the 2 post (single throw), but just with dual posts on each side of the switch no?
Thanks i understand the reasoning for putting the alternator on the battery side of the switch so that main power is cut in the even that the switch is turned off.
I am still not following the 4 post switch theory. Internally the switch is the same as the 2 post (single throw), but just with dual posts on each side of the switch no?
No. All 4 posts are separated once the switch is thrown.
This is how I have seen and personally wired multiple street vehicles. I was in the process of doing mine this way again, but plan on hitting the track and seeing 140mph+, so I know the track officials are going to be up my ***. This is when I ran into all this discussion about the cutoff switches and wiring variations.
All the other 4 terminal ones, for the "alternator" circuit of the switch, smal;l posts are used and I believe it is intended to just be a control wire that would cut poqwer to the alternator, if you had an alternator that functioned that way...which I am not sure if the LS alternators work like this?
All the other 4 terminal ones, for the "alternator" circuit of the switch, smal;l posts are used and I believe it is intended to just be a control wire that would cut poqwer to the alternator, if you had an alternator that functioned that way...which I am not sure if the LS alternators work like this?
Try Summit Racing. This one is rated for 300 continuous and 2,000 surge.
Thanks for the link. I looked into that switch and it looks like the alternator wire can only see a MAXIMUM of 20 amps...This doesnt seem like much at all...at first glance I thought 4 big studs, but its like all the other 4 post switches I have seem, 2 large ones and 2 small ones, which is fair for the alternator to be smaller...but 10 gauge wire and 20 amps max? come on now
Thanks for the link. I looked into that switch and it looks like the alternator wire can only see a MAXIMUM of 20 amps...This doesnt seem like much at all...at first glance I thought 4 big studs, but its like all the other 4 post switches I have seem, 2 large ones and 2 small ones, which is fair for the alternator to be smaller...but 10 gauge wire and 20 amps max? come on now
This is from http://www.bcae1.com/charging.htm
"Current Demand and Flow:
If you have an alternator that can produce 120 amps of current (max) and the the total current demand from the electrical accessories (including the battery) is only 20 amps, the alternator will only produce the necessary current (20 amps) to maintain the target voltage (which is determined by the alternator's internal voltage regulator). Remember that the alternator monitors the electrical system's voltage. If the voltage starts to fall below the target voltage (approximately 13.8 volts depending on the alternator's design), the alternator produces more current to keep the voltage up. When the demand for current is low, the full current capacity of the alternator is not used/produced (a 120 amp alternator does not continuously produce 120 amps unless there is a sufficient current draw)."
I am aware of this. But I will be producing at least 50amps continuously.
2 fuel pumps = 30 amps + chassis electronics + big high current dual speed fan that pulls over 20amp + engine electronics + stereo....etc etc etc. a 10 gauge wire will NOT cut it. I am going to go back to the battery side of a 2 terminal switch using a 4 gauge wire. I cant seemt o find 3 or 4 post switches that can handle high current through all of the posts.
I am aware of this. But I will be producing at least 50amps continuously.
2 fuel pumps = 30 amps + chassis electronics + big high current dual speed fan that pulls over 20amp + engine electronics + stereo....etc etc etc. a 10 gauge wire will NOT cut it. I am going to go back to the battery side of a 2 terminal switch using a 4 gauge wire. I cant seemt o find 3 or 4 post switches that can handle high current through all of the posts.
You can use a 4 pole and on the other side of the 3/16 terminal opposite from the 10 GA and power your fuel pump from that lug and run the 4 GA from the alternator to the battery side of the switch. I'm assuming right now your pumps are fed directly from the battery or directly from the alternator.
The 4-pole from Longacre is just about the only one you're going to find that can handle the correct load. All of the rest only have 20-amp circuits (they're all the same switch for the most part) on the alternator side and this is only good for carbureted applications without high amp draw things like electric fuel and water pumps and fans. So you're stuck with wiring the alternator to only the battery side of the switch, using the bigger 4-pole or getting creative with relays/breakers on the alternator control circuit using the 20-amp switch as a ground for the relay and a switched 12 volt for relay activation.
You can use a 4 pole and on the other side of the 3/16 terminal opposite from the 10 GA and power your fuel pump from that lug and run the 4 GA from the alternator to the battery side of the switch. I'm assuming right now your pumps are fed directly from the battery or directly from the alternator.
Pumps are grounded, and power wires go through 2 seperate 50 amp circuit breakers, with 2 separate 40 amp rated relays and they are triggered on the coil circuit of the relay using 2 ground outputs from the MS Gold. In the event the relay F'ed up, then wiring it ALSO through the 4 pole switch could provide additional protection I suppose. But if the power to the PCM is cut, then the switching of the fuel pump relays should be cut also, effectively doing the same thing.
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Relocated Battery Alternator Wire 
