Rewiring my EFI Magnum - 1970 Dart Swinger

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autopar3000

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Hey guys, I'm going to post some of what I've been up to with my 70 Dart. This thread will be about the rewiring engine and transmission harness of my EFI Magnum equipped 1970 Swinger.

This mini build thread follows a thread where some members helped me figure out how I should rewire the engine: Do I really need the wire from the alternator to the bulkhead connector?

First, a bit on my car. It's a 70 Swinger with a 1994 5.9 Magnum, Doug's headers, Hughes SER0814ALN-14 cam, Mopar M1 Magnum EFI intake, Mopar Performance OBD1 PCM, and 53 mm throttle body. I'm running a 46rh transmission with a 2500 stall torque converter, and a 3.23 gear in an 8 3/4 rear (for now). I pulled the engine out of a retired ambulance turned hunting / camping rig, and put it in my car with the only upgrade being the cam, and the headers which where already in the car from my old LA 318. All the other upgrades came later. The car works amazingly well, and I'm super happy with it.

I'm doing this because:
  • The van harness required extensive modification to work in my car. The PCM was on the driver side firewall of the van, but I wanted to mount it to the passenger inner fender, so lots of wires were lengthened and shortened.
  • I didn't wire it with an ASD relay, which is the relay that powers the coil and fuel injectors. I just wired it to the coil positive with the ignition start and run connected together. It worked, but I couldn't get the need for a relay out of my head.
  • I want to try to get the factory cruise control set up.
  • I want to put the headlights on relays.
Here's where the engine came from, back in 2018:

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The first thing I did was get a "new" Dodge Ram OBD1 engine harness from a guy on FB Marketplace. I also got a factory fuse / relay box from the same kind of truck from a local guy. I got the engine side wiring with the relay box, which included the connectors I need to connect to the engine harness. This way I don't have to hardwire it (like my old setup), so it will be way more serviceable.

With the extra space in this relay box I can add some more relays, specifically for headlights, electric fan, etc, and I'll use those fuse slots where appropriate too.

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I got all the hoses and the alternator moved out of the way. I left the old harness in place and laid the new harness over top. Well, it looks like the Ram harness is a bit long! Turns out they run across the top of the cowl in the full size trucks, so that extra length that's moving the wiring towards the front of the engine is actually vertical in the trucks.

In hindsight I probably should have looked for a Dakota harness, since they look to be a lot closer to what I would need. Oh well, looks like I'll be shortening a few dozen wires.

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Here's me half way through cutting down this section of the wires to the correct length so the harness fits my engine bay. I think it was 9 inches that came out of this section. Soldering and heat shrinking everything.

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And here it is laying in the engine bay all done. Looks like I'll have to move the PCM towards the front a little, but everything else lines up perfectly.


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You’re going to be happy with that when it’s all wrapped up and tidy. Nice work!
 
You’re going to be happy with that when it’s all wrapped up and tidy. Nice work!

Oh for sure! I know it seems a little crazy, but I'm really looking forward to the cruise control. With the 46rh the car is a total dream to drive on the highway, and I'm thinking the cruise will make it that much better.

Here's a little teaser on how I'm going to make that happen. These will probably end up in the ashtray of my center console. I have a generic fan switch, OD switch, and check engine light in there today.

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Oh for sure! I know it seems a little crazy, but I'm really looking forward to the cruise control. With the 46rh the car is a total dream to drive on the highway, and I'm thinking the cruise will make it that much better.

Here's a little teaser on how I'm going to make that happen. These will probably end up in the ashtray of my center console. I have a generic fan switch, OD switch, and check engine light in there today.

View attachment 1716214935

Did I miss how you are going to run the CC (besides the buttons)? Going to use the Magnum PCM to control it like the OEM?

I made plans to do to on my Duster when I was going to put the Magnum EFI on it similar to what you are doing. I planned to run the stock switch on the column, but was going to wire it to the PCM.
 
Did I miss how you are going to run the CC (besides the buttons)? Going to use the Magnum PCM to control it like the OEM?

I made plans to do to on my Duster when I was going to put the Magnum EFI on it similar to what you are doing. I planned to run the stock switch on the column, but was going to wire it to the PCM.

Yes sir, I'll be using the factory Magnum PCM for the cruise. It's controlling the transmission, efi and charging system, so I figured why not give it a try.
 
Yes sir, I'll be using the factory Magnum PCM for the cruise. It's controlling the transmission, efi and charging system, so I figured why not give it a try.

Nice! I completely agree, it has the built in capabilities so why not use them.

Don’t remember the specifics on an OBD1 setup but the OBD2 system I had planned to use had variable resistance on one or two wires to tell the PCM which button was pushed. Is the OBD1 just one wire per button? Is so, should be cake to make it work.

I’m planning to do something similar with my G3 swap, but those commands are on the bus so I have to sniff the codes and build a module to replicate them. Not quite as easy.
 
Nice! I completely agree, it has the built in capabilities so why not use them.

Don’t remember the specifics on an OBD1 setup but the OBD2 system I had planned to use had variable resistance on one or two wires to tell the PCM which button was pushed. Is the OBD1 just one wire per button? Is so, should be cake to make it work.

I’m planning to do something similar with my G3 swap, but those commands are on the bus so I have to sniff the codes and build a module to replicate them. Not quite as easy.

Yeah, the obd1 is dead simple. It's just one wire per button, and another to the brake switch.

Obviously OBD1 is very limited in that it can't be tuned, but but it's what i had from the ambulance so I went with it. Although the obd2 Magnums are not complicated by any stretch. Way more simple than anything needed for a G3 swap!

A while ago I did buy an obd2 harness and PCM and planned to upgrade my setup. Then I found a 46rh and had it installed. So then I would need a 46re to make the OBD2 upgrade work. Then I found a Mopar Performance OBD1 PCM, and put to rest and thoughts of going to OBD2.
 
I bought some of these "Packard 56" terminals and replaced most of the wires on my the engine bulkhead harness. I removed the fusible old link because it was trashed, and I'm wiring that connection into my relay box where it will go through one of the PAL fusible links in the box. The black charge wire won't be coming directly from the alternator like a factory setup, instead the charge wire will be going to the relay box, through a fusible link, then to the bulkhead connector. Very similar to the Rams and Dakotas from the 90s.

I think the Magnum oil pressure sensor uses the same resistance range as my factory rallye cluster oil pressure gauge, so I wired in the Magnum connector hoping I'll be able to see that oil pressure gauge move for the first time ever. I have had a mechanical Autometer oil pressure gauge since forever, but my engine already has a T with the Magnum sensor, so why not give it a try.

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Love those shiny connectors! The only one I didn't change is the brown wire that would normally power the coil, it was still good.

In my application the brown wire and the blue/white wire are spliced together, and they power the Magnum PCM.

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I'm putting the fuel pump wire, the main power wire, and the start / run wires on these bullet connectors. If I can find some better connectors that will support up to 15 amps then I might swap them out, but for now this is how it will be. I think if I put some tape around the bullet connectors I won't worry about them coming apart, and I'm sure they'll handle the amperage loads. Here's the one for the start / run wires going to the PCM input power.

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I'm going to try to start this thing to see if my wiring is OK. I don't have anything hooked up aside from what it needs to run the engine; no transmission wiring, none of the cruise control stuff, etc. Just the bare necessities.

If you look close you can see the charge wire going from the alternator to the relay box (it will be 6 awg when permanent) and the power going from the relay box to the battery (will also be 6 awg when permanent). Somewhere in that spaghetti you can see the orange fuel pump wire, the red wire from the bulkhead that is going to a fusible link in the relay box, and if you look real hard you'll see the black wire that would normally be from the alternator to the bulkhead is going from the relay box to the bulkhead.

I have checked and double checked everything, but you'll notice I'm not brave enough to use the rare Mopar performance PCM for this test. I plugged in my original dime a dozen factory computer for this.

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It runs!!! All I did was turn the key on then off a couple of times, which primes the fuel pump. Then set up the camera and... super fast start up, just like normal. I was later thinking I should have had the belt on it so see if the charging wiring is OK, but I'm sure it will be fine. I hope it will be fine.

I don't usually take video, or even pictures when I'm working on the cars. Only if I need to remember how something came apart. This very much felt like one of those "will it run?" videos you see on car builder shows. "This thing better start or we're going to lose the shop!!!" Lol, looks like the shop is safe for now.

 
With that settled I decided to mock up how the relay box is going to sit along with the cruise servo. This is what I have in mind.

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I like what you're doing I'm collecting parts for similar build. Question: for cruise control what you are using for speed sensor input for PCM.
 
Well, Ill tell ya for a street driver , I like fuel injection...:thumbsup:

For sooo many reasons it was the right choice for me. I especially like that it's an OEM setup, so it's super reliable, and if I do have an issue I can just go to any parts store and get replacement parts.

I do sometimes miss the charm of a carb. Sort of like dialing a rotary phone, winding up a cassette with a Bic pen, or moving the rabbit ears around to get a better picture. What I have now is way better, but it's missing something. The car lost a bit of its soul when I went with EFI, but I would do it again.
 
I like what you're doing I'm collecting parts for similar build. Question: for cruise control what you are using for speed sensor input for PCM.

At first I was using the standard 3 wire speed sensor that was used in the 46RH in 1994. On the 46RH it goes into the speedo cable drive. On the Rams and Dakotas the PCM uses that signal for the cruise control, so it knows when to shift into OD and lockup the torque converter, and to run the speedometer.

But that speed sensor doesn't have a mechanical output for a speedometer, since the gauges in 1994 were all electronic. I didn't really feel like gutting my speedo and putting electronics in behind it, so I changed to an earlier 2 wire speed sensor like what would have been used in the late 80s. Check Standard Motor Products part # SC108. This meant I had to change my speedo cable to one with the smaller connector (I think from an 89 Dakota), but that wasn't a huge problem.

The later 3 wire speed sensors have one power wire from the PCM, the signal back to the PCM, and a ground. The 2 wire I'm using now just has a signal to the PCM and a ground. I was surprised it would work, but it does. I have heard the 2 wire sensors are less reliable than the newer 3 wire sensors, but I'm not too worried. The worst that would happen is I would lose OD and lockup, so I could still get the car home.
 
At first I was using the standard 3 wire speed sensor that was used in the 46RH in 1994. On the 46RH it goes into the speedo cable drive. On the Rams and Dakotas the PCM uses that signal for the cruise control, so it knows when to shift into OD and lockup the torque converter, and to run the speedometer.

But that speed sensor doesn't have a mechanical output for a speedometer, since the gauges in 1994 were all electronic. I didn't really feel like gutting my speedo and putting electronics in behind it, so I changed to an earlier 2 wire speed sensor like what would have been used in the late 80s. Check Standard Motor Products part # SC108. This meant I had to change my speedo cable to one with the smaller connector (I think from an 89 Dakota), but that wasn't a huge problem.

The later 3 wire speed sensors have one power wire from the PCM, the signal back to the PCM, and a ground. The 2 wire I'm using now just has a signal to the PCM and a ground. I was surprised it would work, but it does. I have heard the 2 wire sensors are less reliable than the newer 3 wire sensors, but I'm not too worried. The worst that would happen is I would lose OD and lockup, so I could still get the car home.

Did this exact same thing on my ‘91 Dakota, minus having to swap anything in. I used a ‘95 van PCM for my 5.9 swap and expected to have to add a wire to the ‘92 Dakota engine harness since the ‘92 was still a mechanical speedo and the van used an electronic one. But the signal wire was in the right spot in the harness and I had read it should work so I just plugged it all in. Sure enough, CC and ID all function fine with the 2 wire sensor.
 
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