Battery in Trunk Wiring That Exceeds NHRA Requirements

SpeedThrills

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Please PM me regarding this.
I was posting on another thread regarding this subject, and I am now completely confused.
Specifically, the subject is to put a battery in the trunk, wire in a cut off switch and do it in a way where there’s no hot wires going to the front of the car other than when it is starting. All for the purpose of being race track legal. NHRA (for one) will accept it being wired with wires being hot all the time. This could be dangerous if a wire becomes shorted. NHRA doesn’t care about your car, they just want it to shut off when their personnel throws the switch.
I’m not good with solenoids, relays, continuous duty relays, maxi fuses, fusible links, etc. However, I am good at making safe, sound connections.
I want to ask a big favor of someone. I need specifics as to what wire to hook up to what connection on what solenoid or relay, etc. This thread has what I’m trying to accomplish: questions about battery disconnect wiring
I think a well thought out reply would be a tremendous attribute to FABO. I’ve never seen a post or thread that is completely clear and concise. (I’m sure these posts are clear to you folks who know what you’re doing, but lots of us are not as sure.)
I have everything in that thread. As an example of what details are needed: Please describe what wires go where on the continuous duty relay, and please be careful to distinguish between specific relays, solenoids, etc.
If someone would want to come to my garage and show me, I would pay you and write the process up for FABO. I think as an amateur electrician, I could write it so other amateurs could understand. With all due respect to you professionals, it’s hard for you to see how simple a lot of us need it to be!
Again, please PM me.
 

Mattax

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I don't see anything in his comments that impact the drawing you're following.
The relay there is normally open. There's fusible links (could be maxifuses) on all power forward except for the starter. Thats only hot when the key is in start.
 

Kendog 170

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I can't help with the wiring but I do know some people use a Ford Solenoid at the Battery because it only send power to the starter while cranking. Chrysler starter wire is always Hot.
 

67Dart273

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You HAVE to have something in the way of a relay, or switch, SOMEWHERE.

If you want to have ALL power cut, (and I am a believer in that) there are only so many ways to do that

HERE IS THE problem: Are you familiar with the old wives tale of "testing a charging system" by removing a battery cable on a running car? Allegedly, if you do, and the engine stays running, the alternator is OK

THAT IS THE PROBLEM you face. Whether "1 wire" or multiwire alternator, the charging system will maintain the engine systems with the battery disconnected.


You need a big *** quality switch to "break" the main battery cable, and you need something that will either break the EFI/ ignition circuit, or break the alternator in some way---either break the VR or break the main output.

The SIMPLEST way I know is to use a 4 terminal, quality disconnect switch. Break the main battery with the large terminals, and break the ignition circuit with the other two.

If you happen to have an MSD ignition, that is EASY because the "small red" trigger wire is low amperage.

If you do NOT have MSD you should consider using a relay to fight the voltage drop of having the two wires all the way to the rear, and then back to the front, from the second set of contacts
 

crackedback

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The problem as I mentioned in the other thread. If that CD relay in the middle of the schematic fails and locks in the closed (on) position, what is the outcome. JMO, you MUST consider what happens when things fail, are you in a worse, better or same position as if it didn't fail. In this case, you have a loop that the cutoff has no control over.
 
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pishta

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What if you just wire the negative post through the key switch at rear bumper to ground? A battery hot is nothing without a ground path and if you have no ground hooked up at battery post, then it may as well be dead. Too easy?
 

crackedback

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What if you just wire the negative post through the key switch at rear bumper to ground? A battery hot is nothing without a ground path and if you have no ground hooked up at battery post, then it may as well be dead. Too easy?

Not legal. Positive side must be controlled.
 

pishta

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There you go. It was too easy to be legal. 10-4

That's an interesting take on NHRA techs opinion as quite a few devices are controlled by the switched negative path: fuel injectors, some car audio head units (Korean oem inside), heck Anything can be switched ground controlled....'Cept your drag car!
 

67Dart273

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But switching the NEG side will not kill the engine either, --if it runs on with the alternator
 

crackedback

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I wouldn't wire a car in that fashion, that's how I would deal with it. :)

Whether it's a one wire or a fielded alternator, this is how I do it. The field wires will be killed by the cut off switch at the speed of light via the system power wire/ignitions switch being dead.

p8qI1hX.jpg


I know I posted a pic of my battery tray set up in one of these threads. With my set up, if the CD relay locks closed (on), you are no worse off than if you had a direct live wire from battery to alternator. However, the cutoff switch will KILL the car/engine. The charge wire is isolated from the other side of the cut off switch.
 
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SpeedThrills

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@crackedback
A couple questions, if you would.
-I have an alternator w/ field wires. I know I’m using the blue field. How does this fit into your sketch?
-The blue wire to switched 12v, what’s a good source?
upload_2022-5-12_8-11-18.jpeg
I’m going to have a lot of questions. My electrical aptitude isn’t what it could be. When I get this done, I want to do a write up for us electrical dummies.
 

crackedback

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Hook up the field wire as normal.

anything that turns on with the key in "RUN" is switched. Radio, etc.
 

SpeedThrills

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p8qi1hx-jpg.jpg

@crackedback
@67Dart273
@Mattax
I'm back. I just did the battery in trunk, using this diagram. The only thing I did differently is I connected the pos battery to the left side of the continuous duty relay (CD), instead of using the left side of the Ford solenoid (FS), because I already had a cable that length.

It starts, runs, everything works and the battery is being charged. However, when I throw the master disconnect (MD), only the alternator stops working (system goes to battery voltage). It runs and everything works, as if I didn't throw the switch.

The wire from the small terminal on the left side of the FS goes to the factory starter relay (FSR), in the "middle" so to speak, where the square gizmo helps retain it. (Sorry for the non-terminology)

The wire to "switched power source" is going to an auxiliary fuse box that gets voltage when the key is on. (I used the wire between the relay and the aux fuse box.)

I don't have a one wire alternator. Mine is the original '74. I connected the wire from the right side of the CD to the blue field wire, which I picked up near the resistor that it's connected to. I checked continuity from there to the alternator to be sure it was the correct one.

This picture shows what I did. The cable on the right side of the FS goes to the starter. The cable coming off the bottom, left side of the FS, goes to far side of the MD (marked "ON" on the outside of the car). The cable coming off the near side of the MD (marked "OFF" on the outside of the car), goes to the large lug on the FSR, still in it's factory location. I didn't know what gauge it should be, so I went with the same 1/0 I used everywhere else.

The blue wire on the CD goes to the switched power source.

The wire on the right side of the CD goes to the field wire.

I know I need to fuse everything. I did it bass ackwards. I was as careful as I could be as I hooked up the battery, looking for arcs, etc.
I'll ask about how to protect everything after I get it to turn off at the switch.

What am I missing?
GetAttachmentThumbnail
 
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justinp61

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So when you use MD all it’s doing is killing the power to the CD relay? My positive cable goes through the MD, as does the power feed to the front. The CD relay is activated by a key on power source that is fed by the feed to the front. When my MD it switched off there is no power anywhere past it.

BTW, I used a four post MD.
 

SpeedThrills

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So when you use MD all it’s doing is killing the power to the CD relay? My positive cable goes through the MD, as does the power feed to the front. The CD relay is activated by a key on power source that is fed by the feed to the front. When my MD it switched off there is no power anywhere past it.

BTW, I used a four post MD.
Beats me. I'm just following the diagram that crackedback provided. (That's it in my OP.) But I just looked at the pic he posted on another thread, and it's different. The pic shows a cable between the right side terminals of the CD and FS. The diagram doesn't have that.
6qh5a1z-jpg.jpg
 

crackedback

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Doesn't matter which side the battery cables are on those relays as long as they are consistent.

I do mine with the battery side to the rear and forward to the alternator and starter on front because it makes sense from a visual standpoint.

The jump wire on the CD relay MUST jump to the battery side of the Ford relay.

You could criss-cross the cables on the top relay and nothing would change the function of the system.

If you still have the black OEM charge wire attached at the alternator, that may be the issue.

You don't have the battery and alternator isolated from the rest of the system if it continues to run when the disconnect its thrown.

Also, there is no image of what you did in the post, just an IMG tag
 
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crackedback

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Where is the alternator charge line?

The yellow wire doesn't happen to feed your aux fuseblock, does it?

Just looking at the pic it doesn't follow the schematic unless that yellow wire is off the alternator charge stud.
 
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SpeedThrills

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Where is the alternator charge line?

The yellow wire doesn't happen to feed your aux fuseblock, does it?

Just looking at the pic it doesn't follow the schematic unless that yellow wire is off the alternator charge stud.

Okay. I think I misunderstood you in posts 16 and 17. Because your diagram uses a one wire alt., I thought I was supposed to connect the right side large lug on the CD to the blue factory field. (I have a factory alt.) That's where the yellow wire goes now.

So, the yellow wire should go to the charge stud on the alt? Leave the factory blue field alone? EDIT: Or maybe the charge wire has to be broken somehow by the CD? My lack of knowledge and proper terminology is killing me.

The blue wire on the CD goes to my aux fusebox as a source of switched power.

I feel like I'm getting close.
 
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crackedback

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What does the single wire off the 1 wire alternator do? It charges the battery and runs the car. I have no idea why you would think that is a field wire... a 1 wire doesn't have a field wire.

The main alt charge cable runs to where you have that yellow wire. You use ALL the OEM stuff up front, EXCEPT the OEM black charge wire that hooks to alternator. That black wire powers the car and you need it disconnected to isolate the alternator and battery from the other side of the cut off switch.

Follow the schematic EXACTLY, it works.

You see my picture. The black wire from cd going to right is power to the cut off. The other black wire going forward hits the starter relay. That is the ONLY wires attached at the cutoff switch. I also have a 60 amp maxi fuse in line to the cutoff. No alternator or starter cables.

This is set up like schematic. It's the tray pictured above.
 
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