Battery in Trunk(Yes again!)

[AtlantaSteve]

Ok, battery in the trunk, here we go again.

I'm trying to decide if I want to put the battery in the trunk or not. Here is what I have decided:
1) I'm going to have a Ford 130A/3G Alternator
2) PMGR Mini-Starter
3) Absolutely will have a solenoid in the trunk.

So what does the wiring look like for this? The PMGR starters usually have a constant hot from the battery, but this is not suggested, as you don't particularly want a constant hot going down the length of your car...Since I won't have a constant hot on the starter solenoid, I can't tap that for the constant hot lines inside the car(Headlights, horn, etc), so it sounds like I still need to run a (fuse protected) line, parallel to the start hot. Will I need a third line for the alternator, or can I use this constant hot? I'm thinking of installing a distribution block where the battery currently is, and using that as the constant hot and connection point for the alternator? Is that OK to do? Seems like that'd need to be a pretty big wire, maybe 6 or 8 gauge?

Finally, how do I wire up the solenoid+starter? I had heard that the starter power needs to be hot BEFORE The key is triggered, to prevent damage to the starter. If the Solenoid has cut power to the starter, and is triggered on by the signal from the ignition switch, then power will actually reach the trigger on the starter BEFORE the battery power hits it. (Because of the closing time of the solenoid in the trunk)

You'll find attached a wiring diagram I mocked up, but it suffers from this problem I described above. ANy guidance would be appreciated.

EDIT TO ADD: There should also be a fuse on the line that goes from the battery to the distribution block...forgot to add that in.

 

[joesgt281]

Your final edit was the only other thing I was going to suggest.
I was advised to use a fusible link, although I'm not sure why a fuse wouldn't work just fine.

Regarding the problem you mentioned about power to the starter not coming on until after the switch is triggered, I can't answer that, just to say that mine is wired exactly like you have it shown, and mine works just fine and I have at least 100 starts on it.

 

[AtlantaSteve]

Cool, thanks, Joe. That was just what I'd heard. I was told this is the reason why you should run a separate trigger line from the ignition switch, instead of jumpering the B to the S on the solenoid on the PMGR starter.

I theorized that this:

would work, but was told it would work, but could damage the starter. *shrug* Glad it's working for you...I'll probably end up doing exactly that.

Edit: here's the post where It was suggested this was a bad idea:
http://www.stangfix.com/testforum/index.php/topic,6331.msg76426.html#msg76426

 

[joesgt281]

One last detail....I triggered the solenoid on the starter by using a relay that closes when the ignition switch is turned to the start position. Not a requirement, but it takes the load of the solenoid off the switch, and is put across the relay.

 

[Dennis66stang]

You dont need the solenoid in the trunk if the starter has one on it. Run one 4 gauge wire from the battery in the trunk to the distribution block, from there run a hot wire down to the starter, and the wire from the ignition to the starter.
If you put the solenoid in the trunk you will just have to run more wires then you need.

 

[Jonk67]

Steve, I think your diagram needs to include the trunk solenoid to avoid confusion and maybe color the wires red for always hot, blue for hot during start, etc.

Posted by: Dennis66stang
"You dont need the solenoid in the trunk if the starter has one on it. Run one 4 gauge wire from the battery in the trunk to the distribution block, from there run a hot wire down to the starter, and the wire from the ignition to the starter.
If you put the solenoid in the trunk you will just have to run more wires then you need."

The reason for the trunk solenoid is to only energize the large ~1/0 cable when you're starting, after that it's dead and only a smaller ~8ga. wire is constant hot so less chance of grounding in an accident and it can be fused easily. The start circuit carries such a large amperage load to turn the motor over that it's difficult to fuse/relay high enough not to trip when starting hot, in cold weather, etc. when the amperage requirement increases. Also the fuse/relay would be so high it may not trip immediately if the 1/0 was grounded in a crash and may start a fire before the relay trips. It's a safer setup.

I had a '70 20+ years ago and was Tboned, the rocker panel was crushed, drivers door was touching the steering wheel. Had that happened on the passengers side and I had a hot 1/0 batt. cable running through there I am pretty convinced it would have grounded the hot wire, one reason I'll be running a solenoid in the trunk.

This site may help explain it better:
http://madelectrical.com/catalog/tm-1.shtml
Jon

 

[AtlantaSteve]

Steve, I think your diagram needs to include the trunk solenoid to avoid confusion and maybe color the wires red for always hot, blue for hot during start, etc.

It does include the trunk solenoid. The one, right there next to the battery...that's in the trunk. There is no under hood solenoid, only the one in the trunk, and the one built into the starter. I'm not running 3 solenoids! LOL Good idea about colorcoding though...I just tossed that together without much though...just because pictures are way more clear than a bunch of text describing where every wire goes

The reason for the trunk solenoid is to only energize the large ~1/0 cable when you're starting, after that it's dead and only a smaller ~8ga. wire is constant hot so less chance of grounding in an accident and it can be fused easily. The start circuit carries such a large amperage load to turn the motor over that it's difficult to fuse/relay high enough not to trip when starting hot, in cold weather, etc. when the amperage requirement increases. Also the fuse/relay would be so high it may not trip immediately if the 1/0 was grounded in a crash and may start a fire before the relay trips. It's a safer setup.

Yep, that's why I want a trunk solenoid. As with seatbelts, I don't like to judge others on what they're doing for safety, and will only speak up when I think something is just patently dangerous (Like if someone wanted to have a 4" sharp spike sticking out the center of their steering wheel...I'd probably say something). If you think a hot wire running fore-to-aft is safe enough for you, then that's your prerogative. But I'd feel better with an additional 10 dollar solenoid cutting power to the giant cable when it's not needed.

I had a '70 20+ years ago and was Tboned, the rocker panel was crushed, drivers door was touching the steering wheel. Had that happened on the passengers side and I had a hot 1/0 batt. cable running through there I am pretty convinced it would have grounded the hot wire, one reason I'll be running a solenoid in the trunk.

Jeez! How did you survive a car pushing a door midway through where your body is sitting?

 

[Jonk67]

It does include the trunk solenoid. The one, right there next to the battery...that's in the trunk.
Yep, that's why I want a trunk solenoid. As with seatbelts, I don't like to judge others on what they're doing for safety, and will only speak up when I think something is just patently dangerous.

Ok, couldn't reverse the pic in my head and I didn't see an 8ga. hot to power the alt, etc.
Same here, if it looks safer to me I try to do it but to each his own, we all take risks driving classics, just depends on how much you wish to minimize those risks as you see fit.

Jeez! How did you survive a car pushing a door midway through where your body is sitting?

Being young and stupid I wasn't wearing my seatbelt so it threw me into the passengers door, which of course had no door panel so I got a nice knot/cut on my head from hitting the metal door....knocked my glasses off, sat up and hit the brakes not knowing where I was, I was rolling in neutral towards a ~15ft. drop off to a canal... I'll have to dig out the pics I took of that car post crash.
Jon