6.4 8HP buying advice

[DionR]

I replaced my cabin one because I just wanted to rebuild my harness with new terminals originally. It fixed a lot of issues with flickering lights and flakey switches. I ended up adding a bunch of fuses because that was the easier way to splice power as well instead of the factory setup, but I also needed more power points since my computer was in the cabin and some other stuff I added.

That makes sense. The later cars have a bigger fuse box and mine (in theory) should be in good enough working order to just leave it alone.

Although, as I type this, I realize I will probably want to add the key in and headlight warning buzzer like I did to my '74 so maybe I have more work that I think I do.

As for the ignition switch, I kept my original 67 without issue. I just jumpered two of the pins together and it hasn't been an issue. I want to say that one pin used to feed the coil directly with 12v while cranking for a hotter spark, and the other pin fed the ballast resistor once it was running to drop the voltage down. If you hook the two together they provide 12v all the time through run and crank positions since you don't need a ballast resistor anymore.

You are correct in the 2 positions of the switch. In start it feeds the coil direct (brown wire) and in run it feeds the coil through the ballast resistor (blue wire) along with the rest of the car. And that's one of the things that trips people up sometimes when they wire the PCM to the blue wire and don't realize that wire doesn't actually have power during start. So joining them fixes it, for the most part.

The issue that some have is that there is a moment when neither wire has power as the key goes from start to run. Really doesn't matter...unless the PCM notices it and thinks the key was turned off and then back on. That has caused some real head scratchers. The simple fix is to wire in a button for start and leave the key in run. But it sounds like you haven't had an issue so maybe it is switch dependent, or could be that the OEM PCM's are more sensitive.

My plan to bypass the issue is an F-Body switch. Bolts into the column and the blue wire has power in both run and start. Wiring it is isn't as simple as I would like, but no "simple" fix is ever really simple is it. And like I said, it might be overkill so I will have to evaluate it when I get to that point.

 

[Map63Vette]

That makes sense. The later cars have a bigger fuse box and mine (in theory) should be in good enough working order to just leave it alone.

Although, as I type this, I realize I will probably want to add the key in and headlight warning buzzer like I did to my '74 so maybe I have more work that I think I do.



You are correct in the 2 positions of the switch. In start it feeds the coil direct (brown wire) and in run it feeds the coil through the ballast resistor (blue wire) along with the rest of the car. And that's one of the things that trips people up sometimes when they wire the PCM to the blue wire and don't realize that wire doesn't actually have power during start. So joining them fixes it, for the most part.

The issue that some have is that there is a moment when neither wire has power as the key goes from start to run. Really doesn't matter...unless the PCM notices it and thinks the key was turned off and then back on. That has caused some real head scratchers. The simple fix is to wire in a button for start and leave the key in run. But it sounds like you haven't had an issue so maybe it is switch dependent, or could be that the OEM PCM's are more sensitive.

My plan to bypass the issue is an F-Body switch. Bolts into the column and the blue wire has power in both run and start. Wiring it is isn't as simple as I would like, but no "simple" fix is ever really simple is it. And like I said, it might be overkill so I will have to evaluate it when I get to that point.

Fair enough. The Megasquirt is probably not nearly as annoyed by brief power glitches, or maybe by some miracle I just have a really good switch. I guess I wonder now what would happen if both wires were hot briefly on the original coil setup. Without drawing it out I'm thinking you'd just be feeding both sides of the ballast resistor at the same time, which shouldn't cause a problem as far as I can think. It would need to be a "break before make" kind of switch if it was important they never got connected together on the coil, but guessing it was never that critical back in the day for the brief amount of time they might interact. I'm sure the "analog" stuff way probably a lot more fault tolerant.

 

[davescuda]

Just buy the crate motor and the harness kit. You get a 2 year fact warranty

 

[DionR]

I guess I wonder now what would happen if both wires were hot briefly on the original coil setup. Without drawing it out I'm thinking you'd just be feeding both sides of the ballast resistor at the same time, which shouldn't cause a problem as far as I can think.

I would have to look at it again, but pretty sure that's how the F-Body's did it. The blue wire was hot at all times and the brown wire hit the other side of the ballast resistor and fed both sides during cranking. There was something funky about it though, I think the F-Body setup actually feeds the start side of the coil off the starter relay? So maybe it doesn't have a brown wire off the ignition switch? Now I have to go back and see what I posted about it to try and remember.

Sure enough, the F-Body switch doesn't have a brown wire and relies on an output from the starter relay to send full power to the coil. So the switch never loses power on the blue wire and doesn't have the redundant brown wire for cases like a G3 swap.

Ok, here's how I think this works. Below is the plug end of an F-Body ignition switch (switch on the left):

View attachment 1715596969

Based on checking for connectivity, it looks like the F-Body splits the power and both the red and the pink wires would be hot.

When the switch is in the run and start position, the red wire connects to the blue wire. Best I could tell, that is the only connection with the red wire.

The pink wire connects to the black/pink wire when in the run position only, while it connects to the yellow wire in the start position only.

The black wire between the blue and the yellow connected to the pink wire, but only when in acc.

The small black wire next to the red wire didn't connect to anything that I could tell.

So, to get this switch to run in my '74 Duster, I would need to connect the following:

Duster -> F-Body Ign Switch
Red -> Red
Red -> Pink
Blue -> Blue
Brown -> Yellow -> wrong, should be yellow to yellow
Black -> Black/Pink
Black -> Black between yellow and blue

That would give me a switch that is hot on the blue IGN1 wire in both start and run positions.

The black wire between the yellow and blue wire could be ignore if one didn't care if acc worked on the switch. If it is hooked up, need to look at what runs off the black wire in your car to make sure it doesn't pull too much for the smaller wire.

Hate that the ignition and start/acc power would both be on the same wire then, but that is how the stock system is so at least it isn't worse than stock.

And the corrected info.

But the above swap info is wrong. The yellow wire in the ignition switch should go to the yellow wire in the dash harness, not the brown wire. Unless the brown wire is somehow jumpered to the starter relay.

So with the F-Body switch, what is needed to maintain the brown wire functionality is to use a F-Body starter relay. This relay has an additional pin that is powered when the relay is closed, and in a F-Body, it powers the coil side of the ballast resistor like the A-Body harness did through the brown wire.

 

[Map63Vette]

I would have to look at it again, but pretty sure that's how the F-Body's did it. The blue wire was hot at all times and the brown wire hit the other side of the ballast resistor and fed both sides during cranking. There was something funky about it though, I think the F-Body setup actually feeds the start side of the coil off the starter relay? So maybe it doesn't have a brown wire off the ignition switch? Now I have to go back and see what I posted about it to try and remember.

Sure enough, the F-Body switch doesn't have a brown wire and relies on an output from the starter relay to send full power to the coil. So the switch never loses power on the blue wire and doesn't have the redundant brown wire for cases like a G3 swap.



And the corrected info.

That actually makes pretty good sense. You'd only need the hotter spark while cranking, so why not tie it to the starter relay.

 

[64mopar64]

Just buy the crate motor and the harness kit. You get a 2 year fact warranty

My son bought the crate motor for his 69. Life has a way of delaying projects, the warranty has expired and the engine hasn't been run yet. Also need to control the engine and the thingy between the engine and drive shaft and all the stuff required to control it. Thats why I'm focusing on take outs. The thread was really looking for advice for purchasing a take out. But thanks for the opinion.

 

[DionR]

I have a 2010 Ram NGC PCM to use....

The base harness I have is from an '08 Charger SRT and is missing the VVT and SRV wires. But I have already checked the pinouts for the '08 harness and the '10 PCM and should only have to add the 2 missing wires. So simple enough and cheap. The only real issue with using that harness is that it only has 2 of the 3 needed plugs, but my local Pull and Save has graciously supplied me with a couple more incomplete harnesses for a very reasonable price. So I have the plug and just need to integrate it into the harness and the chassis. There is a chassis plug on the engine harness that I will splice the missing plug into and then it is just the typical EFI swap connections to the chassis like power, ground, key on, start signal, etc. Really shouldn't be too difficult.

Apologies to the OP, I know we kind of derailed his thread with cross talk about swapping. But I was mistake in the above post and feel the need to correct it.

The car harness only has one plug, the orange one, not 2 like I was thinking. So the black and neutral plugs have to be grafted in.

There is a video on YT from Sublime that was a great source for me, maybe it will help. But you have to search for it, it won't link here. Video is called - DIYHEMI Video #002 - Gen III Hemi Swap Basics - Part 2

 

[64mopar64]

Apologies to the OP, I know we kind of derailed his thread with cross talk about swapping. But I was mistake in the above post and feel the need to correct it.

The car harness only has one plug, the orange one, not 2 like I was thinking. So the black and neutral plugs have to be grafted in.

There is a video on YT from Sublime that was a great source for me, maybe it will help. But you have to search for it, it won't link here. Video is called - DIYHEMI Video #002 - Gen III Hemi Swap Basics - Part 2

, it's all good info.

 

[Dantra]

, it's all good info.

Bro.. Wtf did they do to your thread