I'm sure this topic has been covered previously, I can't find it. Wiring a new race truck, S-10 for S/ST. Should the ground from the battery be run to the engine block, battery has been relocated to the rear of bed. Also, wiring a 16v alternator. Again, should the hotwire from the alternator be run thru a switch to the battery or directly to the battery? Sorry if these questions seem rudimentary but my knowledge of auto electric is somewhere between a joke and non-existent.

I'm working on wiring up a 68 Camaro. Found what appears to be a good diagram/directions on proper grounding while researching the same question. Run one ground from batt negative to frame and another from batt neg to engine. Run the usual ground strap from engine to frame. Also run a ground from engine to a ground block mounted on frame as well, which can be used as a location to ground other electric needs, (lights, gauges...). The picture I have of this set up also shows the cutoff switch in the positive batt cable, close to battery. I don't know if that would work with an alternator though. I seem to remember someone telling me to have the alternator wired up with the switch as well, but I have not done that yet. I can't get the picture I have of this to load here. Will keep trying though. Hope this helps,,, more'so, I hope my plan is correct. Have a great day.

Nothing wrong with the above.

You have to put a battery on/off switch at the rear of the vehicle so you might as well pick up a good one and make it a 4-pole switch. Your positive cable will run through the larger lugs and the alternator positive will run through the smaller ones.

You can't go wrong with extra grounds. I prefer welding bolts to different places on the frame and using those as ground points for whatever is needed nearby. A mild steel frame does a good job of continuity, some say a chromemoly one has some resistance in it - on those I prefer to run a full length ground cable.

Here one thing to think about when somebody tells you not to use chassis as a ground due to too much resistance in steel, every time you create another path to the battery you cut resistance in half. I know it’s not exactly in half but if one piece of moly ten foot long has resistance of 100 ohms for example and you put ten pieces in parallel you end up with total resistance of ten ohms. A racecar chassis has several parallel paths built into it so total resistance isn’t what you think.

That isn’t the resistance of moly by the way just using that number for making an example.

I run a heavy battery cable from the battery to the front of the car to a brass stud that goes through the firewall. Inside the car I run a heavy cable to a ground strip with a number of #8 screw terminals for ground. Outside I run a heavy cable to the engine block. At the frt. of the motor I have a heavy cable to the chassis. Battery is in the back so I have a ground wire from the fuel pump, which is in the back, to the battery.

For the alt. there are 2 ways assuming a 1 wire alt. You can wire the alt with a heavy cable direct to the battery, but that cable will always be hot. The other way is with a HD 4 terminal cutoff switch and run the alt cable to it and then to the battery. Buy the switch with 4 3/8" terminals from Cole Hersee.

If it’s a stock frame or mild steel chassis make a #4 wire up and ground the block to the frame, if it’s chromoly do not use the frame/chassis. The alternator should go directly to the battery. I use a relay that is energized with the ignition switch by the battery so the wire going to the alternator is dead unless you turn the ignition on. I also run #6 wire for the alternator.

if I am not mistaken if you don't run the alt wire through the cut off switch the engine will not shut off if you kill the main shut off in case of an emergency. some one else may can speak to this.

ep

quote:

posted January 21, 2020 07:10 AM Hide Post
if I am not mistaken if you don't run the alt wire through the cut off switch the engine will not shut off if you kill the main shut off in case of an emergency. some one else may can speak to this

true

quote:

Originally posted by pauley:
if I am not mistaken if you don't run the alt wire through the cut off switch the engine will not shut off if you kill the main shut off in case of an emergency. some one else may can speak to this.

ep

Not true, if you kill the switch it will cut off the car. Now, if you wire the alternator to the wrong side of the switch it will keep it running. You have to hook it to the battery side of the switch or the battery it self. What keeps a car running is when you hook the alternator wire to the side of the switch that you think is being cut off when you turn the switch off.

Barney,how do you recommend wiring the wire going from the alternator to the battery so it is not always hot?

I use a second disconnect for the alternator that is landed to the battery side of the main disconnect. This way if my main disconnect were to fail I could replace with the alternator disconnect to finish the race and still have a working main disconnect.

Here’s another way of wiring a 4 terminal main disconnect with the alternator wired to the main +12v feed from the disconnect. Wire your Ignition Control to the second set of terminals on the main disconnect. This way the Ignition Control box is isolated from the alternator and will kill the ignition when switched Off.

quote:

Originally posted by BarneyB:

quote:

Originally posted by pauley:
if I am not mistaken if you don't run the alt wire through the cut off switch the engine will not shut off if you kill the main shut off in case of an emergency. some one else may can speak to this.

ep

Not true, if you kill the switch it will cut off the car. Now, if you wire the alternator to the wrong side of the switch it will keep it running. You have to hook it to the battery side of the switch or the battery it self. What keeps a car running is when you hook the alternator wire to the side of the switch that you think is being cut off when you turn the switch off.

thanks BB. I knew it was something like that.

ep

I use 200 amp continuous duty solenoid from Fastronix. With a toggle switch to ground you can have a master disconnect switch near driver and in rear of car as required.
We run 4 gauge alternator wire to the battery with a 60 amp breaker, if there is a short it clicks the breaker.

Grounds need to be heavy duty and you cannot go wrong having a lot of good ground wires. Like the idea of isolating the power and ground to the ignition, they are getting very voltage sensitive and are grabbing a lot of data. "Clean power" is important.

quote:

Originally posted by jbt352:
Barney,how do you recommend wiring the wire going from the alternator to the battery so it is not always hot?

I use a relay that is controlled by the ignition switch, if the ignition switch is not on the wire going to the alternator is not powered.

quote:

Originally posted by BarneyB:

quote:

Originally posted by jbt352:
Barney,how do you recommend wiring the wire going from the alternator to the battery so it is not always hot?

I use a relay that is controlled by the ignition switch, if the ignition switch is not on the wire going to the alternator is not powered.

Barney, Dumb question, but do you put the relay back close to the battery(trunk mount)?

quote:

Originally posted by jbt352:

quote:

Originally posted by BarneyB:

quote:

Originally posted by jbt352:
Barney,how do you recommend wiring the wire going from the alternator to the battery so it is not always hot?

I use a relay that is controlled by the ignition switch, if the ignition switch is not on the wire going to the alternator is not powered.

Barney, Dumb question, but do you put the relay back close to the battery(trunk mount)?

Yes, as close to the battery as possible, less wire that is “hot” all the time.