I have reached the moment in the restoration of my 68 mustang when it was finally time that i start the engine again. i have relocated the battery to the trunk and have 12feet of 2gauge wire running from the solenoid to the starter. i started it three or four times and had it running for about 10 seconds. about the 6th time attempting to start it, it simply would not crank any longer. i have 12V at the battery, 12V at the starter, 12v at the solenoid, 12V at the distributor. now when i turn the key, i hear the solenoid click and nothing else. when i attempt to bypass the solenoid by connecting the two solenoid terminals with a wire, still nothing. i switched starters and replaced the brand new one with the old one-still nothing. i dont know what else to check in order to get it started.
The negative cable has to be grounded to the fender well where it used to be grounded. If not there, it should be grounded to the body somewhere near the engine. The old negative cable had a lug attached to it for this purpose. Your starter worked a few times without it but may never do so again.
You might just be able to connect a lighter gauge wire from the engine block to the body. To test for this, attach both battery cable ends (pos. & neg) to some metal on the upper part of the engine, and the other ends to the bolts on the shock absorber support, or elsewhere on the fender well. When that works, you can buy a new cable of the right length and connect it to the former location on the fender well.
If there is no former location, remove any bolt from the fender well and attach the cable with it.
More of the reason: You have to have the engine grounded to the body in addition to whatever else you have in the way of grounds or you may end up with other part-time electrical components, especially in rain.
Another thing. Unless you have installed a ventilation path for the battery, put it back under the hood so you don’t get hydrogen gas inside the cabin. Battery cases don’t crack often, but if one does…
Why relocate the battery? There is lots of room under the hood for a battery. Put the battery back where it was originally and get the original battery cables replaced with new ones and try again. I don’t think you are getting enough juice from the battery to the starter with the battery in the trunk.
There’s no reason your setup shouldn’t work. Can the engine be turned by hand? Is it possible that the engine is siezed? If the engine can be turned, then I’d go with the other posters that suggest that you may have a poor ground connection between the engine and frame or battery and frame.
Oblivion has a point and a good one.
See if you can spin the motor BY HAND via the crank pulley and optimally by the outside of the main pulley damper…I know most dont have this ability …so use the pulley bolt see if she rotates.
The negative cable is just as important as the positive…
If you have already bypassed the solenoid with a piece of wire or screwdriver…and the starter does nothing…Pull the starter and bench test.
This system is ridiculously easy in its simplistic design…and execution… If you do the above you will figure it out. The starter Bendix might be locked up…after you hear the click…does the wire to the starter get HOT? Do you hear a HUM? If so or not…pull the starter…
Also I hope you put an Optima Battery in the trunk…They don’t mind where or what position they are in…You could mount one of those in the car, above your head and upside down and you 'd still have no probs with it…Dry cell battery…gotta love em…Wet cell…gotta hate em…
Blackbird
Thank you all for the advice. The battery is in the trunk because this is actually a complete disassembly resto-mod and everyting is new. used to be a coupe now a permanent convertible. (the before and after pcis are unbelievable, BTW) nothing up under the hood except engine and a boxed in engine bay. no pulleys at all, nothing on the crank- electric water pump, electric fans, and a small motor for the alternator. the battery is grounded in the trunk to the chassis, but forgot about the ground on the engine. the engine hasn’t siezed, I rebuilt it but to make sure i did turn it by hand also. Bench test was fine on the new mini-torque starter. no wires at all are hot. based on what several of you have offered, this could likely be a grounding issue. I’ll give that a try today. I like the Optima Batery suggestion too.
one other question i had, Is it possible to use a marine battery in a car for more avaiable cranking amps?
Yes it is possible to use a Marine…BUT Optima has that covered and then some…disregard ANY and ALL lead acid batteries…Trust me. The Optima is a VERY COMMON item on Hot rods and it deserves this positioning They are VERY solid items…very strong…Dont/CANT leak… They’re simply “the bomb” to put it simply.
Now if you grounded the batt to the chassis…this should work…As the Stang is actually a uni-body…No? Double check everything as I said B4 this is a SIMPLE SYSTEM…not much complication going on here…so just take it slow, you will find the issue.
You could for Shits and giggles run a negative wire straight from the batt to the starter body or bolt…see if this changes things in a positive way…lol… If so …you found your issue.
Blackbird
Honda Blackbird has the correct solution. A negative battery lead with the same gauge as the positive should be run to the engine block to properly ground the engine. Grounding it at the starter is even better. Even with a uni-body car, chassis grounding through the body is not a guarantee of a strong ground. Not having a dedicated ground line to the engine is the most likely cause of your problems.
I’m also wondering about your idea to run the alternator with an electric motor. This will actually cause the battery to drain faster, meaning, you’ll waste more electricity running the alternator than you’ll get from the alternator producing electricity. There is no such thing as a perpetual motion device, and this ain’t it. Whatever power the alternator needs to produce, the electric motor needs to produce more to turn the alternator and overcome the friction forces and electrical loses. This car will only run as long as the battery charge holds up, because this alternator set-up will do nothing.
Both Franken-stang and I thank you very much. here’s a little b4 and after…
NICE…well done… You mean you did all that and you cant get that starter working ?! LOL 
Also how did you re-enforce the body after chopping off that top? That aint no simple thing to do…an X brace under the car maybe?
Now that you ran a ground to the body…did you run a fat wire from the body directly to the BLOCK? Cause it wont make that negative connection thru the motor mounts…and if it does…it is not sufficient…
Blackbird
First, you need to run a copper ground wire from the battery to the engine block, the will be too much resistance using the body as the ground plane. That is OK for accessories, but not for the starter. You can get by with 4 ga for the ground wire if you want because you will still have some current going through the body. You also need a minimum 8 ga stranded or braided wire between the engine and the body, two of them would be better, just in case.
Next, you have to drive the alternator with the engine, unless you have a separate gas powered motor just for the alternator. With so many accessories being run off the battery, you need a high amp alternator as well.
Normally, the comment about the H2 fumes from the battery would be valid, but since your car;s cabin is now permanently ventilated to the atmosphere, that isn’t as much of a problem. But you do have to make sure that hydrogen is not trapped inside the battery box. That could turn the box into an unintended IED.
“…but since your car;s cabin is now permanently ventilated to the atmosphere, that isn’t as much of a problem.”
I’d still be concerned about hydrogen gas in the trunk. Your life is still in danger even though the explosion will occur in the trunk. And it would be a shame to blow up such a fine restorod Mustang.
He’s gonna buy himself a nice new OPTIMA battery…RIGHT? All his concerns will then be whisked away…
“But you do have to make sure that hydrogen is not trapped inside the battery box. That could turn the box into an unintended IED.”
jt, I think we are in agreement.
I would ventilate an Optima battery too. I also would recommend the Optima battery for safety reasons, and vent the compartment too, just to be safe.
To answer the OP’s other question, a marine battery would not supply enough amps to crank the engine. A marine (or deep cycle) battery provides power for longer periods of time, but not the high current for short time needed for starting.
Dude, battery in trunk must be sealed, non-vented type regardless if it’s a convert or not. Big safety issue. Forget marine deep cycle- not meant for short duration high loads. A marine starting battery with sufficient CCA is OK but must be sealed. No advantage in marine type over auto and probably cost more.
Do not use the body for any electrical grounds, especially high current demands like the starter motor. You’re doing a custom, no need to tie anything to the chassis anyway. That’s a cheap method some manufacturer chose. You can do a much better job by modifying the interior and engine bay harnesses. I love your approach. All my restifications are focused on minimal stuff visible in the engine bay. Love the look. Everything is tucked away. I even go so far as to custom bend stainless tranny cooler lines for my automatics and hide them inside the frame.
You can use the frame for your starter return if you choose not to run two wires to the front. Perfectly acceptable to do so. Block to frame up front with the fattest braid you can find (or double up), battery minus to frame through grometted hole in the trunk with a length of insulated black 2 ga or better. Use star washers between the lugs and frame, after grinding it clean, to bite in and provide good connection for a long time to come.
Good luck on your project!
I’m not sure Optima’s have vents Keith…methinks they do not… I can check…or we can pull the website to see… I believe the “dry cell” is a bit of a misnomer…I think the “acid” is in a thick paste like form…it cant or doesn’t leak out… They are friggin great actually…they cost a bit more but they also last a lot longer and will NOT harm your paint or metal as well.
If it is in his trunk…trust me there is enough air leakage to ventilate the area…no need for excess.
IF you want to hide the connection of the ground…You can sneak it thru the floor or firewall and go to a transmission bell housing bolt…so that you cant see it from the engine bay? Get creative, you will find some way to get it done covertly.
TwinTurbo, I may have misunderstood your post a little, but the body still has to be grounded. I agree with not using the body as the ground for high loads, but you still need to ground the body.
yes Honda, all that work and cant get the starter to turn over! Haha. fabrication and creative design are my strong points…not really electrical. 
Optima battery yes. already bought it. i stiffened up the body by fabricating some heavy duty subframe connectors. the only thing original to the car is the unibody (which was chopped) and the rear axle- replaced everything else. i did 100% of the work. not much i dont know about this car. im on my way to the garage now to try out the grounding advice. i’ll post my results in just a little while.