RJM Harness Fuses

[Izzy]

Hey Guys,

I have read several articles and just can't figure one thing out. I understand the Mega fuse item from the alt to the battery. But I have read snips about putting a fuse between the battery and the rest of the body wiring. This confuses me.

I am running the Explorer motor and serr, RJM Harness, and 4g alternator. The RJM harness has several fuses in it. Does that cover between the battery and the rest of the body harness? Or do I need another fuse somewhere?

Sorry for asking a question that has been asked before but I'm still confused.

Thanks guys.

 

[Viperwolf1]

RJM fuses protect the RJM harness only. Body harness protection was a 16g fusible link attached to the battery side of the starter solenoid.

 

[Izzy]

Are you referring to the wire that comes from the starter?

Also, what about grounds. I understand it is best to run a ground from the battery negative side to the block and then from the block to the frame and from the block to the body. Where on the block is the best place to conenct this ground? Can I go from the battery to the bolt that mounts the alternator to the serp bracket?

As for the body ground, can I run it from a intake bolt?

 

[Steve83]

He's talking about the fusible link wire in zone E4 of this diagram:



The best place for the block ground is near the starter, because the starter uses the most current. And the body ground can come directly from the battery terminal. Read these captions:



This shows the fuse needed for an upgraded alternator:

 

[Izzy]

I know I am asking stupid questions but I just don't get it yet.

I am using the mini starter and a 4g alternator and Ryan's Harness for the EFI conversion. I have a purple wire coming from the harness conencted to the Starter raley s port, I have a battery cable going from the relay to the battery, I have another cable going to the starter.

As for connecting to the body harness, I just have the 3 wires that connect the RJM to the body with one going to the ignition.

I just went and looked again and I did find 3 wires that I forgot about. Brown which I don't think I need, yellow that goes to a fuse and then to body somewhere, and then a red\blue wire. These were connected to the starter relay before. Where do they go?

I also found 3 wires that were conencted to a duraspark before. They are:

Red\green
Yellow/black
and Black

Where do these go?

 

[KRAWLER]

Im with you, doing a 4G with the RJM harness.

I have all of RJM hooked up, removed the voltage regulator (I assume none of that wiring was needed). Coming out of the firewall factory I have 2 large black wires. I am assuming 1 is the starter solenoid and the other is the original return for the Alternator as it looks as if it referenced in that direction.

Question is which wires are needed? The red/brown go on the starter relay, then on hot side of relay the battery and incoming power from original harness with the purple RJM wire, the the other large terminal that goes directly to the starter?

Do I run the charging wire with big breaker directly to the stud on alternator to hot side battery?

 

[Steve83]

Izzy
This one shows how to hook up a mini starter; it only takes a new small wire from the relay to the starter:

 

[Izzy]

Steve,

Thank you what I was missing which I believe I have now figured out is I didn't have any extra wires going to the body anywhere. Since then, I noticed I had a yellow and a red\blue wire that came from the starter relay which I then plugged back in. If is fused so I shouldn't need any additional fuses.

Piecing together the different diagrams and discussing it with Aaron, I'm 90% sure I got it figured out now.

 

[DirtDonk]

So many questions!

...I have all of RJM hooked up, removed the voltage regulator (I assume none of that wiring was needed).

Correct, but you might find a use for some of them later, so you don't necessarily need to cut them off, or hide them permanently.

...Coming out of the firewall factory I have 2 large black wires. I am assuming 1 is the starter solenoid and the other is the original return for the Alternator as it looks as if it referenced in that direction.

Correct. The one originally on the starter relay has to go back there, under the battery cable. It's the power for all the truck.
The one that originally went to the alternator can be saved for later use too. Find a power distribution stud and mount it somewhere convenient. Put the unused Black alternator wire there to power other accessories, since it's full battery power on a 10ga wire.

The red/brown go on the starter relay.

Should be Red w/blue and it still goes back on to the "S" terminal of the relay/solenoid. That's what starts the engine.

then on hot side of relay the battery and incoming power from original harness

By incoming power, I assume you mean the large Black wire? If so, then yes, that goes on the same side as the positive battery cable. It's no longer incoming power from the alternator, and is now exclusively outgoing power from the battery to the rest of the vehicle.

with the purple RJM wire

This wire goes underneath the Red w/blue wire on the S terminal. It's only purpose is to tell the ECU that the engine is attempting to start.

the the other large terminal that goes directly to the starter?

Only on a stock-type starter. If you have a mini-starter, like Izzy, then wire it like in Steve's diagram, with the starter cable to the same side as the battery, and the small wire that activates the new starter, goes to the old large post where the starter cable used to go.

Do I run the charging wire with big breaker directly to the stud on alternator to hot side battery?

Yes.

Paul

 

[DirtDonk]

Steve,

Thank you what I was missing which I believe I have now figured out is I didn't have any extra wires going to the body anywhere. Since then, I noticed I had a yellow and a red\blue wire that came from the starter relay which I then plugged back in. If is fused so I shouldn't need any additional fuses.

Piecing together the different diagrams and discussing it with Aaron, I'm 90% sure I got it figured out now.

As you figured out, you still need most of the old wires from the rest of the harness. Ryan's wires only function with regard to the engine management, and don't replace anything on the rest of the truck.
So your Red w/blue is still needed to energize the starter.
The Brown is no longer needed.
The Purple wire only tells the ECU that you want to start the engine. It does not actually start the engine, which is why you still need the old Red w/blue wire.
The old wires from the voltage regulator are not needed immediately, but might be used in the future for other duties. Cap them off, but don't necessarily cut them off and render them permanently unusable.
The bit about using a fuse in the line that feeds the rest of the truck is if you're either running an entirely new chassis harness, or no longer wish to use the existing fusible link in the Black w/red wire. If you keep it as-is, and it's working fine, there's no reason to change it out to a fuse, except for convenience. A fuse is easier to replace if it blows out on the road or trail. And a fuse blows faster than a fusible link, which is good now that you no longer have the alternator charging through that wire.
So it's entirely up to you which way to roll.

Glad you got 'er almost there. I can almost hear it running already!

Paul

 

[Izzy]

Paul,

Thank you very much for helping me verify everything.

Thanks Steve and Viper for the info and diagrams as well.

Last question on this topic.

Can I run a ground from the battery to the block near the alternator and then run a ground from the intake to the body? If so, this would prevent me from having too many wires running all over the engine compartment.

Thank you

 

[Viperwolf1]

Can I run a ground from the battery to the block near the alternator and then run a ground from the intake to the body? If so, this would prevent me from having too many wires running all over the engine compartment.

Yes, that is how I would recommend it be done. Battery to block ground needs to be at least as heavy as the starter cable.

 

[KRAWLER]

That's awesome, thanks again guys.

 

[Izzy]

Ok, I said last question but I thought of a new one. Any idea what size bolt goes in the hole that is on the lower passenger front side of the motor that many are using to ground the block?

 

[Steve83]

It's better to daisy-chain your ground wires instead of breaking them up. Start the body ground at the same bolt as the block ground.

Of course, it's even better to splice them all together inside the battery negative terminal. That would give you a VERY short body ground wire from the battery to the sheet metal, and it wouldn't cross anything. Why go from the body (battery tray) to the block, and then back to the body?

 

[mattt]

Paul,

Thank you very much for helping me verify everything.

Thanks Steve and Viper for the info and diagrams as well.

Last question on this topic.

Can I run a ground from the battery to the block near the alternator and then run a ground from the intake to the body? If so, this would prevent me from having too many wires running all over the engine compartment.

Thank you

I just wired up my Bronco the same...efi, explorer alt, GR mini starter. I don't know if you like stock-factory stuff...but I do. I used a factory ground cable for a few reasons. 1) I had it, it came with the engine I bought. 2) It captures all the grounds you need...... in that it has a ring terminal on the block end, another ring terminal half way up the cable for frame ground, & a wire off the batt. terminal for body ground along with the neg battery clamp. 3) It was very close to the perfect length.

I don't see re-inventing the wheel on my build which is why I'm trying to use as much factory stuff as I can. If it's good by the factory, it works for me. I also used the factory positive cable for the same 3 reasons. It makes wiring up the GR mini starter idiot proof....all you have to do is hook up the ends to their respective posts. The only thing with the positive cable is you'd have to switch your starter solenoid/relay/switch(on the fender) to a 90's vintage solenoid which only has the 1 post for the "from the key" wire(red-blue stripe). I also moved the solenoid up on the inner fender skirt right behind the battery....really cleaned up the wiring and the look of the inner fender.

In addition, I re-purposed a few wires in the stock Bronco harness(that I didn't need with the EFI and Explorer Alt) instead of running new wires across the engine compartment.