Thread: 1968 Plymouth Valiant 1st Gen HEMI

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The darn weather and my back have pretty much been keeping me out of the shop for the last couple of weeks. Rather than sit around and wait for better weather I started on a couple of small projects that I would normally do much later in the in the process. One of those projects was to figure out the wiring for the MSD 6A and backup Chrysler Electric Control Unit (ECU). I don't know if anybody here is running a Chrysler Electronic Ignition but if there is this might prove helpful.

A lot of you here know that after I build a car the big test is usually to drive it from Arizona to Illinois and back (normally around 4000 miles or so), something I hope to do in the Valiant. About half of the trip is done at night and anybody who has driven through the Southwest knows there are sections of the trip where there is nothing for miles and miles but miles and miles. I usually carry a box of “just in case” parts with me, the usual things like belts, hoses, bulbs and fuses ect ect. I also carry things that might be not be on the local parts store shelf that would a show stopper if I couldn’t find a replacement. Sitting in a motel in downtown nowhere for a day or 2 while I wait on something to be shipped in is not fun so I usually also carry a spare complete HEMI distributor, wiper motor and switch, alternator (1 wire 10SI) etc.

I like running a MSD 6A on these old HEMIs (which I have convert to Chrysler Electronic Ignition), it really helps with cold starts and drivability as the engine warms up. To me the 6A boxes are a bit pricey just to have one sitting in a box in the trunk “in case”, their also PIA to change out along the side of the road at 3AM. The compromise I came up with on my 57 Plymouth was to mount and wire both the MSD box and a Chrysler Electronic Ignition Module to separate plugs that can be connected to the cars wiring harness. If the 6A box goes out it’s a simple matter to unplug it from the wiring harness and plug in the Chrysler module. I’d usually run the car on the Chrysler module once in a while just to make sure there are no issues if I ever needed to use it.

I built the 57 Plymouth almost 20 years ago and used a 6AL box. I’m using a new 6A box on the Valiant and there is a bit of difference in the wiring between the 2 so I basically had to redo my wiring diagram. Of course the wiring on the Chrysler ECU hasn’t changed in decades, although I have noticed there have been changes in the color coding of the wiring harness that plugs into ECU depending on where you get the harness from. You might also notice that there are some circuits on my diagrams that don’t show a color code. That’s because I haven’t built the wiring harness yet and the color(s) I use will depend on what wire I have on hand (I’ll pencil in the color on my copy of the diagram once I get it all wired into the car).

These are the wiring diagrams for the 6A box and Chrysler ECU I started with.

wiring MSD CHRY org by M Patterson, on Flickr

And these are the diagrams that show the 6A and Chrysler ECU wired to the 8 pin plugs I used. I actually only needed a 7 pin plug but 8 pin plugs seem to be a bit easier to find.

wiring MSD CHRY 8 by M Patterson, on Flickr

Finally the wiring harness plug that connects either the 6A or Chrysler ECU to the cars harness.

Wiring Harness by M Patterson, on Flickr

If someone decides to use this as a guide for building a backup ECU system keep in mind IT IS ONLY A GUIDE. There are differences in the wiring between the 6A box I’m using and other MSD boxes depending on the model and probably age. As I noted there are also differences in the wiring color coding on the Chrysler ECU plugs depending on where you source them from. From my experience the wiring/plug that goes into the distributor have always been orange and black wires, but you never know what’s out there in the aftermarket if you use a replacement pickup assembly. Basically it’s up to you to verify the wiring for your specific car/components.

Anyway for me it’s worth the extra effort to go I through if for nothing else than just for the peace of mind when I driving far away from home and shop. It was also a good mind exercise on a cold rainy day LOL.


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Mike, are you using Molex plugs?
I remember when I had a 75 Duster there was a starter relay, I believe that's what it was, that gave me fits and I always carried a spare.

Ken I used Molex plugs on the 57 Plymouth. I'll be using this style on the 68, not sure what their called.


s-l960 by M Patterson, on Flickr


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With the 57 Plymouth and the 37 Dodge gone it looks like this is the new normal in the shop.

new normal by M Patterson, on Flickr


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I missed the departure of the '37 Dodge truck!!:Where did it find a new home?

The east coast, somewhere around the Florida Georgia line.



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I'm just muttering to myself about it being 20 years (!) since we watched you do the '57 Plymouth..........

Time does manage to get away from us. My Friend who bought the car invited me to his new place (complete with new shop) Friday. I hadn't been there before.......nice place!

Anyway the 57 now lives on the lift (with his 71 Charger underneath it). We were going over the car, top and bottom. I remembered the build like it had only been a couple of weeks ago.



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It was a good Sunday. Cade is going to be coming out on Sundays for the foreseeable future to help with the Valiant. We’re still working on getting the engine and transmission to its final location so I can get the mounts built. In the process we found we had an interference issue with the steering column.

column 1 by M Patterson, on Flickr

Fortunately it looks like it’s going to be a non-problem. The column in the Green car is a floor shift unit and considerably shorter. As it was a bottom of the line car when new, I suspect it originally came with either a column shift automatic or 3 on the tree. The column was probably changed out when it was built with the 508. Hopefully it was from another A body, but after looking at it I don’t think there will be any issues converting it for the EPAS electric power steering.

column 2 by M Patterson, on Flickr

For now we just pulled the steering column from the mock-up car. Cade’s tuning into a pretty decent mechanic and he sure fits under the dash better than I do.

The weather is supposed to be pretty decent this week so hopefully I’ll get some more done during the week.




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Very nice work on the project. Was it harder to let the truck go or the 57?

Definitely the 57. The 37 was fun and a fun (if somewhat long) build. I just couldn't bring myself to put an automatic in the 57. By the time the 57 sold though I was ready for it to leave......it had starting bothering me a lot that it was such a neat car but I couldn't drive it anymore.



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Ok time for another update. On the bright side I went ahead and ordered more stuff for the 68, a lot of which has come in. There’ve been several days where it’s felt Christmas around here. You’d think at my age and the number of cars I’ve built that getting new parts in wouldn’t make me as happy as it does LOL. Anyway I figured I’d go ahead and get the stuff I’ll need while it’s still available/before the prices go up again. Among other things I got; the electric power steering, an MSD 6A, a spare 110A single wire alternator and a 650 Edelbrock AVS2.

I’m still going to pull the intake off and have the plenum divider milled down for a Holley Sniper EFI but I’ve heard of bad things happening trying to use an aftermarket EFI on a fresh engine that hasn’t been completely broken in. The AFB that’s on the engine now does ok on the engine stand, but it’s only 600 CFM and I figure the 650 will probably do a bit better when the engine is actually in the car and driving.

On the saving money side the good news is I’m able to use up a lot of the new “spare parts” I have on hand. I’ve got a new stereo, gauge set, cruise control, GPS, ignition ECUs, spare distributor (for the “just in case” travel box I carry) and a bunch of little odds and ends.

On the down side I’m doing some wiring (and will have a bunch more to do) and when I checked my terminal box almost all of my connectors, shrink tubing, and electrical wire needed to be replenished. I got most of the small stuff ordered and then started looking for a wire assortment (in different colors) on-line as locally the wire assortment (especially in different colors) is pretty limited.

I noticed most of the wiring I was finding was marked as “CCA” which I don’t remember seeing before. It turns out CCA stands for Copper Coated Aluminum. I looked into it a bit more and found that it’s not really good to use in vibration prone environments as the aluminum wire will work harden and eventually break. Anyway I looked a little harder and found what’s supposed to be USA made stranded solid copper wire. It cost about twice as much as the CCA wire but I figured why take a chance. Admittedly the CCA would probably last at least as long as I’ll be able to drive, but if there’s something I hate it’s repairing something I recently built and it’s even worse if it happens to be wiring.

Anyway I figured I’d pass on what I found out about the CCA wire in case you haven’t heard about it yet. If it’s not already on the shelves in the local parts stores, I suspect it soon will be.



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I noticed that stuff when I bought some jumper cables, the cheap ones are all aluminum. Sneaky little trick to make us think we are getting a bargain.

Sunday again and Cade was out for most of the day. We spent most of the day clearancing the transmission tunnel for the Over Drive unit on the 46RH. Yea by we I mean mostly Cade LOL.

z Trans tunnel by M Patterson, on Flickr


By this afternoon we pretty much had it figured out.

OD 1 by M Patterson, on Flickr

OD 2 by M Patterson, on Flickr

We have a bit more trimming to do and I’ll need to weld some flat-stock in to gain the strength back before we call it good. We were able to adjust the engine bit more. We’re not quite there yet but we’re close to getting it to the sweet spot it will live at.



On those days where I’m not up for anything too physical I’ve been doing projects where I can sit at a bench. One of those has been the gauge cluster. While the setup currently in the green car is reasonably functional for a race car I’m not real wild about it for a street car.

68 Cluster 1 by M Patterson, on Flickr

The factory gauge cluster is actually pretty nice and it looks like they put new gauges in when they restored it……of course none of them work, I suspect I’ll find they’re not hooked up. The cluster looks nice enough I really don’t want to destroy it for aftermarket gauges…….but hey that’s why I bought a parts car. Destroying this cluster didn’t really bother me too much LOL.

68 Cluster 2 by M Patterson, on Flickr

I never did find a 1 ½” fuel gauge so I decided on a 2” Autometer fuel gauge. This made gauge placement a little more challenging but I finally settled on this.

68 cluster 3 by M Patterson, on Flickr


I wanted to leave the headlight, wiper and hazard flasher switches in the original location which meant I would need at least a portion of the back plate which is also used to mount the cluster back in the dash. A little time with the cut-off wheel and I had the part I needed.

68 dash 4 by M Patterson, on Flickr

I got new gauge face cut out, black paint on it and have it assembled. There is still a bit to do/re-do but I think I’ll like it better than what is currently in the car.


z GC by M Patterson, on Flickr


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Remember my other Grandson Austin?

austin torque wrench by M Patterson, on Flickr

Somewhere along the line he got a bit older (13) and bigger. Yeah he’s turned into a full blown teenager.

z Austin 3 by M Patterson, on Flickr

Frankly I don’t think he’ll develop an interest in cars like his older brother and that’s OK. His interests seem to lie in other things one of which is electronics. As long as Austin’s interested in doing this, there’s going to be plenty of electrics to do.

I’ve been teaching him the basics on DC wiring (a lot of which he already knew). We’ve moved from there to teaching him how to read wiring diagrams and now we’re at the point where I’m having him actually starting to draw the diagrams out himself……and what better project to start him on than a custom gauge cluster for say a 68 Plymouth Valiant.

z Austin 4 by M Patterson, on Flickr

The next project (hopefully sometime this week) will be to actually connect the circuits to plugs. I figure we’ll get in some wire splicing, (both soldering and crimp connectors) shrink tubing, reading an ohm meter etc etc. I figure once were done we’ll connect up the dash lights so he can see they actually work.

I made it a point a long time ago that I will never force the grandkids to be out in the shop with me. If there is something they have an interest and want to learn I’m more than happy to teach and help. If they don’t want to be there that’s OK too. This is one of those things that Austin doesn’t mind coming out to grandpa’s dusty old shop to do and we’re both enjoying it.

God only knows what direction Austins’ life will take him, but you can never have too many skill sets.


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