Is it kosher to use a body mount bolt (inside the trunk) to ground the negative battery cable to? I really don't want to drill another hole in my trunk floor and I have a bolt (that goes directly into a nut welded to the frame) just an inch or 2 away.
That should work fine. Just make sure that there is no rust or paint that might keep you from getting a good contact.
The battery ground should ALWAYS go the engine block, and with the battery in the trunk, 2 gauge cable minimum with 12 volts. The body and frame should then be grounded FROM the engine block.
i personally believe in overkill on grounds...grounds [or lack of] cause all sorts of gremlins. i have them on body,both ends for lights,frame,engine block...all on a steel car!
I agree. I don't think you can have too many grounds. And not a stupid question at all. And V8 Bob, I have my battery in the trunk and the ground goes to a nice chunk of cleaned up frame and then I have to grounds from the block to the frame. It works for me but I was wondering if I should expect some problems in the future with this set-up? chris
Yep! although I have run the ground cable to a bolt in the trans. tail housing to make the cable a little shorter. It becomes an issue when trying to start the car when the engine is up to temp. That is when the cables need to carry the most amperage. I've fought that fight. Set it up right and it won't become an issue. Check out the restored cars from the 60s-70s like the muscle cars to see where the factory connected the ground cable from the battery. It will almost always be bolted to the block or a bracket that bolts directly to the block.
I've always had a heavy woven ground strap from the block to the body, from the body to the frame and from the frame to the block. I plan on keeping these. Also, this isn't a big nailhead anymore, now it's just a 350 Chevy. I'll try to body bolt, if it doesn't work, I try something else. Thanks for the answers.
I believe the frame makes the best ground, period. Then ground the engine, and everything else, to the frame. But that's just me.
Every car I've seen with a front battery has had the negative cable going to the FRAME, not to the engine. But the current doesn't have to travel very far along the steel to get to the engine ground strap.
I like the ground going to the frame is well. All grounds are created equal, just that some grounds are more equal than others. I keep them as short as possible, a throwback to my stock car days when I'd weld a stud to the roll cage or frame, whichever was easier to do. Also always ground the engine to the firewall, look at how many factory cars had those piddling woven straps that were various shades of green, and they still worked. Bob
Well, the thing is...if you use the frame as the ground from your battery your gonna need just as big a cable as that battery cable from the frame to the engine anyway. Otherwise the starter will be overloading the smaller wire most use as a frame or body ground. You end up with a big cable to hide at the engine bay anyway... All the Chevy cars I've worked on in later years had the main ground to the Alternator bracket. That IS where the "power" comes from and it needs a good ground to complete the circuit AND its easy to access for inspection and cleaning. The body and if necessary the frame used a smaller gauge cable to complete the ground circuit to the lights etc. The main draw thru the battery and battery cables is the starting motor. Look at how big they are to reduce resistance for the starter. Move the battery farther away and you need larger gauge cables to keep the resistance to minimum levels. Using short cables to the frame and then from the frame to the engine will add joints for corrosion to start and not save a whole load of money anyway. Personally...I'd run a full length cable of adequate size right to the rear of the engine, then complete the ground circuit thru smaller gauge cables to the body and the frame. The difference in price would be minimal compared to being stranded because the car needs to cool off before starting or the frame lugs corroded and lost contact or whatever...
Not to mention the embarrassment after driving 100 miles to a show, stopping at registration and have to wait an hour or so for it to start again so that you can go park. Been there done that it's not fun. I didn't believe it either back then. Someone convinced me to move the ground cable from a dedicated welded stud (I had planned ahead) on the frame over to the tail shaft. It never happened a gain. I fought it for almost a year. It will never happen to me again. Nothing is more embarrassing than a cool hot rod that won't start.
0 guage welding cable from the batt(rear mount) on both cables to the front...ground to starter/engine mount bolt....power the box(MSD or MALLORY) right off the welding cable...in addition i also ground to frame at the battery....no nitrous pops or hot starts ever
I've done it both ways but agree with those who say it is best if you can run the ground cable back to the block. And take into consideration that for the longer runs you will probably want a larger cable to lower the resistance level. The main thing is still clean contact areas and tight connections no matter how I do it. And definitely put a ground strap from the engine to the body on all steel bodied cars. I replaced a lot of shifter cables on Pontiacs in the 70's and 80's because the cable had welded it's self to the housing after someone had left the ground straps from the firewall to the valve cover bolts off when changing valve cover gaskets. I've also see more starters, alternators and batteries replaced when they didn't need to be because the ground strap wasn't tight on the block end or the block or bracket had too much paint under the strap to allow good electrical contact.
When I did the frame ground, I'd make up a nice fat ground cable that went from the block to the body, usually at the firewall. We had this huge Thomas & Betts crimper at work and of course they donated the lugs. Bob
The way I do rear mounted batterys is to drill a hole through the floor, attach the ground cable to a bolt going through the floor, then attach a ground outside the trunk to the same bolt, then to the frame making a bulkhead for the ground. Clean the area well and you get a good ground to the body also. Now at the engine bay you will want to make your usually ground loop: engine to frame, frame to body, body to engine, all using the appropriate size cable or straps. If you do it this way you will always have a good ground through the vehicle even if you lose connection on any one ground
Everybody has covered ground basics so I'll tell you a funny story about an engine grounding problem from my youth that relates to the subject. Back when I was sixteen I mounted the battery in the trunk of a '65 Mustang Fastback. I ran a large 00 cable from the battery to the starter solenoid and bolted the ground cable to the trunk floor. When I went to start the engine it cranked slowly and then smoke started coming out from under the dash. I thought, this must be some kind of a coincidence because I have not worked anywhere near the dash. Without thinking I reached under the dash and grabbed the choke cable housing and it left miniature barbecue scorch lines on my hand, it burned me really good. It never occurred to me that the choke cable housing had become the ground circuit for the starter. I would have thought that with all that metal somewhere there would have been a good ground from the engine to the frame but there was not. What I did not understand at the time was the engine is mounted in rubber, the exhaust has rubber hangers, the trans is mounted in rubber, the rearend is attached to the springs which are mounted in rubber and the rear shocks are mounted in rubber. In the case of my Mustang the only place that 300 amps could find its way back to the battery was through that little metal choke cable housing that was grounded to the bottom of the dash. I perfectly understand not wanting to drill holes in the trunk of your car. I practically have to go to therapy if I drill a hole that wasn’t there from the factory (it makes it really hard to build hot rods) I don't think it is necessary to run a separate ground cable all the way back to the engine but you do need to have a large cable from the block to the frame capable of handling the starter amperage. Even though you have the ground cable hooked to the body in the trunk I would still run another 10 gauge ground from the engine block to the firewall. Maybe even another one from the firewall to the dash, the more grounds the better. Always remove the paint from any grounding point, and it is a good practice to use the star type washers that bite into the metal between the cable and your ground, they only cost a few pennies and they make a big difference eliminating voltage drops. Jerry
Jerry, thanks for the story. I have had that happen too. My engine grounds are usually short battery cables with eyelets on each end.
I had some 200 Strand Welding Cable that I ran on my Merc when I put the Battery in the Trunk, The Ground to the Frame & the other to the Starter and 4 Grounds from the Engine to the Frame Never had a Problem and No Voltage Drop per say Just my 3.5 cents
I believe V8 Bob has it right. Ground to the engine then engine to frame. Engine to body. The woven flat ground straps are best bar none. I was taught that electrons move down the outside of the cable, more cable area better electron movement, less resistance. Thats why more strands work better than less strands when it comes to cable. In my opinion that is. B
Ok, here is my perspective as a marine electrician building large battery banks to run yachts. Oh please remember, a lot of my theory is overkill for cars, but is the soundest from an electrical standpoint. First off, the battery is the source of energy, we all agree on this. For ground, I run a ground from battery to frame, at that same point of contact to frame, I then have my motor grounded, and my body grounded. Now we have all primary ground at the same potential. I then install a ground buss for all lighting, which I wire as "2 wire" for less voltage loss. Remember the complete circuit is back to the battery, and ground will take strange trips on the way back if you let it. I always take my charge circuit (alt or genny) direct to my main positive buss, which feeds my main fuse block. Doing this ensures charging takes its cleanest path back to the battery, which then supplies the juice to the car. And your grounds take the most direct path back to the battery. This ensures cleanest power and lowest voltage loss. One last note, welding cable cannot carry as much current as rated battery cable. I recommend going to your local marine supply shop (if you have one) and buy tinned marine grade heavily stranded cable and use closed end lugs and heat shrink. just my 2 cents
All of this is good stuff. Has anyone ever come up with a good way to prevent the "clean when new" ground points from corroding after a while? Would it make sense to braze a spot around the hole? Tin it with solder? Maybe I'm worrying too much.
This reinforces the idea to run the primary ground from the battery to the engine. The least connections means less chance for corrosion later. Most auto electrical problems are related to ground and are frequently hard to find. The voltage will read on a meter, but will fail under load.
I agree Handyandy welding cable is designed to carry a lot of current/amps and if you take some welding cable and a set of parrots beak clamps you have the mother of all jumper cables.....got 2 sets of them
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