BATTERY GOING TO TRUNK WHAT ABOUT THE GROUND?

[shoebox1.1]

im going to put the battery in the trunk with the cut off switch in the rear panel. i WANT to have a terminal block (BATT+) mounted on the firewall to power relays and msd. im worried about the ground circuit back to the battery. i thought about making ANOTHER 1 ga NEG cable and terminal block at the firewall (for the relays and msd and wideband o2 sensor.) this way im NOT using the car as a ground. i do have a 6 pt roll bar that i could go from the batt neg to rear bars..... then another cable from the front bar to the engine? or is the body conductive enough? would be nice just to have it "at the rear rollbar tube" in the trunk and thats it. ground everything up front to the body/engine plate any input would be appriciated!

[SunbirdMan]

I used the chassis, but I doubled up on the ground cables in the trunk. The negative cable goes to one side of the spare tire well then is bonded to the otherside with another bolt to the chassis. Just one cable from the passengerside cylinder head to the chassis. Works fine and doesn't need 12 more feet of expensive 1/0 wire.

[cjbiagi]

I don't see any problem using the body/chassis as a ground as long as everything is clean and solid. Run a good ground to the rear of the cage and then work from the front of the cage for your connections. A good solid ground between the chassis and engine is imperative. Remember, orignally the heavy negative battery cable went right to the engine and everything else fed off of that. So you need a heavy gauge between the cage and engine to duplicate that. The engine has to have a solid ground for the starter draw.

[shoebox1.1]

sounds good.. i have a nice piece of cable that i can go from the motor to the body/rollbar. should work good thanks

[Astre-mutt]

I did something similar to what you where originally thinking about. Not not because a chassis ground wasn't good enough, but because I don't like drilling holes in my car. Since I have a panel wagon, I have a extra storage compartment behind the sets. I put the battery behind the passenger seat. I only had to drill two small holes through the floor to mount the battery. These where the only holes I had to drill to do the hole conversion. I ran a ground & hot wire from the battery to the firewall, through the inside of the car. At the fire wall I ran the positive cable through a 3/4" hole that was all read there from the factory. The ground wire I ran up to a small hole that was used for a rubber plug to hold the under dash insulation. I put a 5/16" bolt throw it, with a matching cable on the other side that runs down to the engine. This acts as a chassis ground, and an engine ground.

I'm not saying this is a better way. Just less destructive for my situation. Below is a pic of where the negative cable comes throw the fire wall, and down to the engine.
Just for the record, there is three screws that hold down the battery tray. One of the screws is in a unused factory bracket.

[spencerforhire]

The chassis of a uni-body car(even without a roll cage) can handle more current flow than even a large cable. A rear mounted battery should be grounded to the nearest convenient point, preferably where the metal is more than one layer, like a pinch-weld or reinforced spot(like a roll bar mounting pad or suspension point).This spot needs to be free of rust and paint, and a nut and bolt(with a star washer) is better than a self tapping screw. Same thing applies for the engine end of the circuit. Obviously, on a full or sub framed car, all three need to be grounded- engine, body AND frame.
All this being said, I do like astre-mutt's ground point on the firewall- what a convenient place to hook up a test or timing light. To go a step further, there could be a 12v+ one beside it( with a plastic or rubber bushing to isolate it where it goes through the sheet metal). These are often seen on the back of race cars as a spot to hook up the battery charger.

[beakerztoyz]

in mine i have a ground in the trunk, but as of now the wire {strap} from the engine to the body is stock and the mechanic told me to use a bigger one aparentley that helps on cars like ours

[shoebox1.1]

thanks for the replies and ideas..

[shoebox1.1]

went ahead and made a short ground wire 4ga high strand count from the batt neg to the rear rolll bar downtube plate. im going to use the rollbar for the ground cable.

[shoebox1.1]

well it worked! my chassis alone is a perfect ground. 12.58 at the batt terminals and 12.58 at the ford solonoid (using the fender as the checking ground). zero losses im happy