Originally my flathead had the battery ground strap connected to a boss in the driver's side head. But my aluminum Offy head has no equivalent provision. And to better show off the shinny new flathead engine, I plan to relocate the battery in the trunk of this 50 Merc.. Running a cable from battery positive to the starter solenoid is a natural. BUT the battery ground is yet another thing. While grounding the battery nearby to the frame or body would be adequate for lighting etc circuits, it certainly isn't adequate to provide current to the starter. The starter does have a rear mount bracket into a pan bolt. Would that work? If not, where to connect the ground cable from battery? Have any photos of your trunk mount? Incidentally, I am using a hybrid starter with 12v FE field and original 6v armature/bendix. FYI a 2/0 6ft battery cable is $40 and 4/00 is $50...excellent quality from BatteryCablesUSA.com.
Battery to a ground on the ch***is and the engine would have a ground strap to the ch***is too, in fact I think ive got 2 ground straps from engine/gearbox to the ch***is - one ground from a bolt on the engine to ch***is and another ground from a bolt on the bellhousing to ch***is. Both my cars have the battery in the trunk and the ground to ch***is and ive never had any issues with starting in 17 years. The battery cables I use are about 2/0.
Why do you say "certainly isn't adequate to provide current to the starter"? Did you think this up all by yourself or is someone "helping" you? That is the way everyone else does it (except the old Morgans with wood frames). Charlie Stepehns
I was always told to run the ground from the battery to the engine when you do the rear mounted battery. You lose power at every connection. If you have a bad connection it is easier to find. You need to remember each cable is 4 connections. The cable to the terminal end, terminal end to battery, ect. Then the debate if the steel conducts as good as the copper. On most cars I have ever done this I have connected the ground to a bell housing bolt.
Provided you clean the contact points and have a ground strap from the engine to the frame it is perfectly fine to ground it to the frame, it’s a much bigger conductor then the wire you are going to run to the front. Oh and find a new source of information on your electrical needs.... All the new cars with a remote mounted battery are grounded to the ch***is, don’t overthink this. You only have a voltage drop at connections that are poor, do it properly and it’s fine. Sent from my iPhone using H.A.M.B.
You may get 20 pages of responses here, 10 pages of "ground to frame in the rear" and 10 pages of "run a ground wire up the frame rail to a bolt on the bell-housing". I'm sure, given good clean connections, that both will work fine. Sure, new cars with rear or under seat mounted batteries, are grounded to the frame at that point. I've just always felt (and it may be just me) that 80 year old metal might not be as conductive as a dedicated copper ground running to a terminus at the front. Either way will work. It's a personal choice. Use star washers on all connections. Now let the debate continue.
Out the bottom of the trunk pan... use a grommet... and to the frame. Keep grounds short and simple. I'll go overkill with the gauge size and an extra ground from the engine block to frame is good too. With the stock cars, I'd weld a stud to the roll cage in a few spots.
Absolutely either will work, if you run a wire to the front, make sure it’s big enough to handle the amperage Sent from my iPhone using H.A.M.B.
I grounded the battery's at the frame when I mounted them in the trunk. Never had an issue. Then grounded the engine to the frame with those grounding straps they sell in the parts store. Steel doesn't conduct as well as copper or br*** but the m*** of the cars frame and body outweighs the little bit of resistance different is materials..
I think the problem a lot of people have is that they use under sized ground wire ,even some of the trunk relocation kits undersize them. I'll even seen imported wire that i know was mislabeled with the wrong gauge. Some may get away with using it if they come off the battery and go right to the frame but if you prefer to go to the block you have to step up the gauge.
How about a picture of that "shinny new flathead engine". And make sure you have good body to frame grounds.
If the battery has a good ground to the frame it really doesn't care if it's in the trunk, under the hood or below the floor board. Ground is ground. Just make sure everything is well connected with the correct wire or strap size. Sent from my LG-TP450 using The H.A.M.B. mobile app
I've only had trunk batteries with the stock cars, so far. With those I'd use regular old battery cable and crimp lugs onto them with a 5/16" or 3/8" hole to make up my extra grounds, engine to ch***is, engine to firewall.
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