Trunk mounted battery and grounding

I have a buddy with a '55 Chevy, trunk mounted battery. He relied on the body and frame for the ground. What a nightmare. We added a dedicated ground cable from battery to engine block. We also added three ground straps from the engine ground connection to the frame and body. I forget what gauge cable we used but it was very thick, like welding cables. No more problems after that.

Two ways to get that ground that I can immediately think of. First would be to drill a hole in the trunk floor that would be adjacent to both the battery tray and the frame, then push a grommet into it and run that ground cable through the grommet and attach it directly to the frame. Pretty much everything electrical in a car soooner or later goes to ground by means of the frame. Even if in the original engine bay location, the battery ground might go to the engine block but somewhere else there will be a ground strap from the engine to the frame. With the battery in the trunk and grounded to the frame, the engine can also be grounded to the frame by means of a short strap or section of cable to guarantee good continuity. Just make sure wherever the groundwire lug is attached is an area where the metal is clean and paint/dirt free.
The second way is a variant on the first. In this scenario, the hole would get drilled but instead of a grommet, a 3/8ths stud would be set in place instead so that it can accept a terminal lug both in the trunk and underneath by the frame. Cheapest way to do that is to cut a short section of all thread and then add nuts and locks as necessary. With the stud in place, the battery ground cable goes to it, and then underneath, a second strap or cable goes to the frame. What this gets you is both a good body ground and a good frame ground as well.

Thing to remember with long battery cables is that resistance increases over distance, hence the need for the heavier gauge cable. Going to ground as close to the battery as possible and using the frame for that purpose lets you use lighter gauge cabling and still get a good strong ground for whatever circuits need it. Just remember to add a ground from the cabin (firewall) to the engine; they were typically used by the factory but tend to disappear as excess wiring during a build or engine swap



Nick

From the spare tire well:
Connects to a 250A rated busbar and branches off
1 forward to the firewall
1 to the floor with a stud welded to the trunk floor
Then through a pass through to the frame via another stud

Firewall distributes to another busbar arrangement then to the engine block with a 4 gauge cable, then to the frame with another 4 gauge cable at the fuel pump boss on a Small Block.


There is no such thing as too long of a ground, or to little ground connections. Just too small of a cable. I’m running 2/0 gauge ground and main power with a 1 gauge charging cable from the alternator to a busbar.
These cars have worse metallurgy than a wet paper bag, put as many grounds in as you can stand, imo.

Battery to engine block with a single large gauge wire, period.

Two smaller grounds, one from body to block and one from frame to block.

Everything likes the path of least restance,(myself included) Continuity is no different.grounds are relatively cheap to make (or even a pre-made lug to lug negative cable from the part store works well)and always a good idea. I made a body to frame ground strap for my pick up using the braided portions from 3 pieces of spare 3' coax.one time I found less noise when running both the positive and negative directly to the battery with one of my radios.

I did the battery to frame in the rear, then frame to block up front, then there's already a block to firewall that grounds the body. So essentially three #2 ground jumpers.

Connect everything to the frame. Don’t need a ground cable all the way to the front. But don’t ground to the body and expect it to transfer to the frame cleanly. Ground the engine to the frame and the body to the frame. My race car ran fine with the battery in the trunk. Cranked a 15:1 565 just fine.

Battery to frame. Then frame to block. Did plenty of cars like this and they cranked perfectly.

I imagine, there is the odd set up like this. Then someone has problems with a poor connection. Changes to a single wire from battery to block, then condemns the to frame method.
Learn to find the poor connection somewhere and fix it instead of changing to another wire.

we can all agree that as old as these cars are they've been through a few hands and thing's like grounds can fall to the wayside with time/people.I'm sure that small stock batt to fender ground was sufficient at best for a stock ride but after adding stuff to them it becomes a little undersized.