Rewiring a Classic Mustang

Discussion in 'Classic Mustang Specific Tech' started by pyroman, Jan 16, 2011.

  1. I thought I'd share with you my experience rewiring a classic Mustang using a modified American Autowire (AAW) chassis wiring harness. This thread will be an update as I go because I am writing it in the midst of installing the kit. Now while the kit I am using is AAW, much of the information and methods I use can be transfered when installing other wiring kits, such as the Painless kit.

    Now a little background.

    This chassis harness I bought is made for "modified" Mustangs. By modified they mean that you've added aftermarket electrical upgrades, i.e. electric fan, electric fuel pump, one wire alternator, electronic ignition, so on and so forth. For more information on this particular kit see the AAW website.

    1967-1968 Ford Mustang Wiring Harness

    Why did I buy this kit?

    When I was shopping around for a chassis I had almost predetermined what I wanted, the Painless harness. They're a well established name and everyone seems to rave about them. Well after consulting the minds of stangnet I decided that AAW was the kit for me. My main reason for choosing the AAW is that it offered more than the Painless kit and cost less. Some of the features it has that the Painless kit doesn't are:

    1. Larger fusebox
    2. Includes new ignition switch, new headlight switch, new dimmer switch
    3. Includes a large gauge wire for one wire alternators with a fusible link already integrated into the wire. I thought this was neat because my one wire setup was a bit bulky and awkward.

    Those are the biggest ones that spring to mind, check out my original thread for more comparison.

    So onto to the installation!

    First, here are some pictures of what came in the kit:

    The case was very nice, good first impression


    I had taken the main harness out of the box at this point, so don't worry! These are the supplemental kits. They include for example a fuse and relay kit, terminal kit, rear wiring kit and a few others.


    Here is the main harness laid out on my bed


    Fuse box. Each spot is labeled, standard on pretty much all cars but very nice for something aftermarket, specific to your car.


    Relay bank for the headlight switch, fog lights, horn Enables us to run high powered halogen lights or if you're running stock lights, keeps that headlight switch from burning up! (I've gone through a few). Also good for aftermarket fog lights.


    Coming up, Step 1, familiarizing yourself with the harness and instructions.
  2. Thanks for sharing! I'm looking forward to seeing your progress. I'm leaning towards the AAW kit right now, but it'll be at least 6 months to a year before I need it.
  3. I used a universal harness and if I had to do it again I would get the AAW.
  4. Step 1: Familiarizing yourself with the instructions, the harness, and all the components.

    This would seem obvious to most, however if you are anything like me you're so eager to get started that you'll just jump into the project before familiarizing yourself with what everything is, what has to be done, and the steps they have to be done in. When you're dealing with an entire car's wiring harness you'll be glad you did this.

    You'll save yourself a lot of time and headache in the end by spending a little extra time in the beginning reading and examining everything included in your wiring kit.

    I began this by examining the instructions. AAW gives you 10 pages of instructions, printed front a back for a total of 5 individual pieces of paper. They present the instructions as a wiring diagram. The first page is essentially a user friendly wiring diagram of the entire main harness. (I don't have any pictures of the instructions but they can be downloaded from AAWs site 510056 3.0.pdf)

    As you can see (if you clicked the link) the harness is subdivided into 9 circuit branches each of which have a number of other branches coming off of it. Essentially the rest of the instructions break down these branches by identifying the wires in the bundle and giving you detailed instructions on what it's function is and where to route it. It starts with branch 1 and works its way to branch 9 which is the order you install the harness in.

    So my first goal was to take the mess you saw laying on my bed here


    and make some sense of it, organize it if you will. At this point I went through each page of instructions branch by branch, found the wires it was identifying and marked the bundle with some masking tape and a marker. AAW was nice enough I found out to have zip tied all the wires together already so the bundles were already established, so don't clip the zip ties yet! (I'm not sure if I will keep the zip ties or not when it comes to the actual installation, I'm leaning towards yes.) Once I figured this out after going through the first branch I carried on with the labeling for my sanity's sake and also just to make myself familiar with what was in each branch.

    After I finished with all of that this is how the main harness looked


    Some of the wires were very long, putting them in a roll and holding them in place with some masking tape made it look more organized (which inspires confidence) and just makes it easier to lug around.

    So what is there to do now that you know the harness backwards and forwards? Well I'll tell you shouldn't do next (learn from my mistakes :lol:) and that is to mount the fusebox. I'll get into that a little bit more in my next post and

    Step 2: Getting organized and removing your old harness.
  5. god i wish someone made a harness like that for 71-73 mustangs :(
  6. Hmmm… The OEM style 71 harness is available.
  7. what? you mean the entire underdash harness is available OEM??
  8. Great thread, give us more!
  9. Step 2

    This will be a two part writeup as I have yet to completely remove my old wiring harness. I did remove the engine harness shortly after it shorted out and "let the smoke out".

    At this point you're probably wondering where you should start. The AAW instructions are not structured in a way where they say..."Step 1 - Do This." Like I mentioned previously they outline the wire hookups, how it should be done, roughly how to route the bundles and generally what order to do it in. As far as mounting and routing the whole thing it doesn't exactly say when to do that.

    My idea to start tackling this process was to first mount the new fusebox. In my last post I mentioned that this should not be the first thing you do. The reason I say this is that once the fusebox is mounted in place it becomes very difficult to manage the wires and routing them correctly through and under the dash will soon become you're nightmare. Luckily for me, once I mounted it and looked at the mess I decided there is no way I'm going to fool with this while I have the fusebox mounted. Before I got any further I decided to consult the minds of stanget to see if leaving the fusebox unmounted while the branches are routed is advisable, it turns out that this was the case.

    However, with all that said, it isn't the worst idea to at least get the holes drilled for the fusebox as a first step. At this point I'll give a little writeup on how I did that before I get on to the true second step of this process.

    Alternative Step 2 - Fusebox Mounting Holes

    For the 67-68 cars, the fusebox mounts in the same general area as the old fusebox, right above the accelerator pedal. See pages 6 and 7 of the instructions provided in my previous post. AAW provides two templates for the drilling the necessary holes, or should I say hole. Only one is actually needed. One of the templates is for drilling from the engine bay side and the other is for drilling from underneath the dash. I thought I'd better be able to access the area from in the car because I have my engine in the car. After doing this though it might actually have been easier to do it from the engine bay side.

    As I mentioned the instructions provide a template for doing this. But when you get the kit and look at the instructions you'll notice they are printed front and back so if you cut the template out of the paper they give you then you just screwed up the directions on the other side. So I took a sheet of tracing paper and copied the template onto that and then transfered that onto a piece of cardboard so I could have it on something sturdier.

    When I started peering underneath my dash, a few things became clear. One, I was going to have to remove the blower motor if I wanted any chance of getting to the fusebox location. (I have an A/C car, I don't remember if the blower motor is in the same spot for the non a/c cars.) I also have a center console and determined it would be easier if I were to remove that too. So after about 15 minutes of cursing and struggling I finally got the blower motor out and got down to business.

    View with the template in place


    Unfortunately the hole that has to be drilled is way up at the top of the template. I think you can just barely make it out at the very top of the next picture.


    The instructions say to use a 1/8" drill bit. I go to my stash and find I have a few. Good thing to because I ended up getting the hole drilled in an unconventional fashion. I say that because while I have a small drill, only 12V, I was having a difficulty getting it up into the space under the dash to drill the hole, even with the drill bit all the way in the collet. I got the drill bit at least on the hole and tried to get it started. Five seconds later, snap! Drill bit broke, damn. Well I figured, it's shorter now maybe I can fit the drill in there. Positioned it and it still didn't fit very well. Decided to try it again, snap! Broke the damn thing again. :mad:

    I sit back for a minute trying to figure the best way to tackle this. I look down at the now nub of a drill bit and figure, what the hell I'll stick it in the chuck and see what happens. At this point it's only like 3/16-1/4" long. However this time it does fit and works like a charm, drilled right through. :rlaugh: I don't really recommend breaking your 1/8" drill bit twice in order to do this but hell it worked for me.

    Just to give you an idea of how it mounts and the mess that follows I'll share a couple of pictures.


    After looking at this I decided it was going to be really difficult to manage all this with not only my fusebox mounted but my old wiring harness still in place.

    I decided to pull the fusebox and re-evaluate the situation. This brings me to the true Step 2.

    I ended up coming to the conclusion that before I dive into this installation I really needed to get organized. I needed a clear, clean workspace first and foremost and I needed to organize the tools I'd be using. This is just one of those things that will make your life so much easier. It's something that definitely should be done prior to any project and this one is no exception. In fact this demands organization. Think of the massive amounts of tiny components in the supplementary packaging. You want to keep track of those things, fuses, connectors, hardware, etc. I don't have a huge amount of workspace, only about a 1/4 of a 2 car garage but for something like this you could honestly manage with even less. You just need a "home base" as I call it. Somewhere you can lay out all the components without the fear of losing something. In my case I have a workbench that's about 6 ft x 2.5 ft.

    On the topic of tools and organization I've got a small list of electrical tools you'll more than likely need to do this.

    - Wire strippers and cutters
    - Ratcheting crimper (not necessary to have a ratcheting crimper but I prefer them)
    - Soldering iron and solder (I'll update with the solder I end up using)
    - Heat shrink assortment
    - Heat gun or hairdryer (which is how I used to roll)
    - Multimeter
    - Some kind of bundling means (electrical tape, zip ties, wire loom, etc, I'll let you know what and what combination of things I use)

    Those are the big ones. If I realize I've missed something I'll update this.

    Once you feel that you are adequately organized it's time to pull that old harness out if you haven't already. I just finished getting mine out today, I'll hopefully get a little guide together by tomorrow evening. This isn't particularly hard but I have a couple of tips that might make things go a little smoother.
    bchampion likes this.
  10. Oh wow, this is a great thread! I'll be doing the same thing hopefully later this year to my 67 coupe. Thanks for taking the time to make this writeup!:nice:
  11. Step 2 Continued

    Getting the old harness out is what's on the menu. This isn't the most delicate and precise operation but then again you don't want go at it with a pair of box cutters either. I'll give a few tips to make it go a little smoother. Since I already got the engine and front light harness out I'm going to focus on everything in the dash. Of course knowing POs you'll probably encounter a few surprises or add ons. In my case a horribly installed alarm that hasn't worked in the years I've owned the car.

    First thing you should do is remove your steering wheel if you haven't already. You'll be spending alot of time on your back under the dash...hmm that didn't sound right :rlaugh: It might even be easier with the front seats removed unless you feel liking getting acrobatic, like me apparently. I've been stubborn thus far and haven't pulled them out. If you're any taller than me (I'm 5'10) you probably won't have much of a choice.

    Ok first thing to disconnect will be your instrument cluster


    This is easy, there is one big connector, your speedometer cable, and maybe a few stragglers like grounds. You can really see the damage in my harness.


    It's good to pull your radio or whatever you are using for your tunes.


    Yeahhh that white connector didn't come that way from the factory


    Now that the instrument cluster is out, there is room to work. One more thing has to go though, and that is the heater duct hose.


    Voila, more space.


    Now it's time to disconnect. First you'll want to unmount your old fusebox if you haven't already. I disconnected everything I could find that terminated at things I was not replacing. (Heater control, wiper motor, door switches, etc.) I don't have many pictures of this process because it was a lot of rummaging around pulling on wires to see if they were free etc. Here are a couple I did manage to snag.

    I believe I'm holding in my hand the connectors for the heater control switch. I could be wrong though :lol:


    I know this one for sure, it's the connector that goes to the rear harness.


    Once you have most of the wires disconnected you'll have to remove both the ignition switch and the headlight switch.

    For the ignition switch I followed the guidelines in the factory service manual. First you have to get the lock cylinder. This is actually a cinch. Put your key, rotate it left to the accessory position, then insert a pin of some sort (I used an allen wrench) into the small hole on the lock cylinder and rotate the key to the left even more. (It should be able to go past the ACCY position) Once in that position, the whole thing should just slide out.

    In order to get the switch out though you still need to get the bezel off. On 67+ cars it was threaded onto the ignition switch, which from what I read is an improvement. However, the manual says I need some special tool to do this. To hell with that I think and I try a couple of different things to try and get it out, nothing working to well. I then glance down at my sockets and wonder if one would fit in there well enough....



    Turns out the 3/4" deep socket was made for this job. Fit in snug enough to allow me to get a good grip on it and yet didn't get stuck or do damage to the bezel (not that mine is immaculate anyway).

    You'll also need to get the ignition switch out. This has a similar threaded bezel. (Sorry I have no pictures of this one :doh:) This is just as easy though, especially with the instrument cluster out of the way. Just depress the rod release button on the side of the switch and pull the rod out. There will be a phillips looking "hole" for lack of a better word left. I read about this trick on here I think. Just take a big phillips screwdriver and unthread the whole thing. Comes out in a jiff.

    Now you should have everything off needed to pull that old nasty harness out. Here is mine


    Empty dash


    Landscape view


    All that other wiring is from an extra few circuits I added to my car to accommodate things like electronic ignition, electric fan, 3G alternator etc. I will have to rethink it's wiring now.

    After you finish this it's good to neaten up your tools, your car and parts. Make things a little more orderly for your next step. It's also nice to take a break and rethink what you'll be doing with the next part of the project.

    After some tidying up



    (Yeah my floor pans are crap)

    Up next, putting this SOB in the car!
  12. god bless you, this will come in so handy later on - and get a duvet cover for that comforter, LOL, jk
  13. First Problem

    Well guys and gals, I've run into the first road block. It should have dawned on me earlier but because I have a factory in dash A/C the mounting location AAW specifies for the fuse box is not going to work. The blower motor will not be able to clear the fuse box.

    So I'm sort of at a crossroads here. Short of going radical there really isn't any other place under the dash that the fuse box will fit. Of course I could just put it...somewhere but I want this to be done right.

    The other thing I'm considering is just ditching the in dash A/C altogether and just put in the regular heater box, blower motor, etc. The A/C doesn't work anyway and took all the A/C components off.

    Stay tuned!
  14. I would not ditch the A/C. In the future you may want it. I Have a 70 with A/C although not hooked up - everything is there is ther in case I decide to do later.
  15. I've been meaning to warn you about a bad experience I had. When I had the floor pans and rocker panels replaced, the shop did not pull the wires for the rear lights, speakers, or convertible top. To my chagrin, I later discovered that they had melted most of the plastic off in places causing shorts and such. When the time comes to fix/have fixed, be sure to keep those wires in mind, especially since you will have this nice new wiring.
  16. Thanks for the heads up. I want to try it myself in order to save money but it's something I'd like to avoid either way!
  17. Question: Does anyone know if the pink wire in the engine bay harness, named "Ignition Feed - coil" can be used to supply the switched 12V power source to a MSD box? It says in the description "...or be used as the ignition power source for an aftermarket ignition module such as MSD or "Duraspark" module." I assume module=box but I just want to make sure. Does this wire have switched power when cranking?

    Also I'm working on new updates for this thread. Should have some stuff up later tonight.
  18. Alternative Fusebox Mounting Locations - For folks stuck with In-Dash A/C

    As you all know I ran into some issue mounting the fusebox because of interference with the in-dash A/C blower motor. I spent the day trying to solve this in the easiest possible way. Turns out it wasn't too bad. So you lucky dogs, you get tips on two fusebox locations!

    After spending an hour or so screwing around under the dash I emerged back broken but with a solution that appeared like it would work. But first off if you don't have one of these tools


    Get one! (A tip from a fellow 67 owner on VMF) They make drilling holes or any other drill function so much easier in tight spaces, like under the dash. I grabbed mine from Lowe's for $20. Also a standard, small, right angle driver would be very nice too.

    I chose to shove the fusebox as far left as I could manage. So basically as close to the pedal support assembly as I felt comfortable with. I've circled the locations of the mounting holes in the next picture.


    At the top right I have a green "X" circled. Now the only issue with this spot is that the firewall is not 'flat' there. So the green "X" is sitting further back than the hole near the steering column. I decided to make a cheap shim out of wood. Of course you could do this step much classier than me, like using a nylon spacer or something. I chose to do it this way because it would be quick and I couldn't find a #12 sheet metal screw long enough, locally anyway.

    So above and below that green "X" I drilled two holes with my nifty new drill attachment for the wooden block. Just used a piece of 2x4 I had laying around, the offset was about right.


    I mounted it in it's spot, what do you know it fit the first time! Not bad for eye-balling more or less


    You'll notice it's not sitting flat. I took it off and trimmed a corner of it (not pictured)

    Here is the fuse box mounted on the bottom screw. I haven't yet secured the top screw to make fooling with the wires easier.

    I did this all with the blower motor in it's housing. It would have been easier if I had removed it but it would have been difficult to put it back in with the fusebox in place. If by chance you are considering doing what I am on in-dash A/C car, remember to leave some slack near the fusebox because if and when you have to remove the blower motor you'll have to unmount the fusebox and rotate it out of the way.

    When I did this I already had the bulk of the circuits routed in roughly their locations. As I mentioned in one my first posts it will be easier if you route the wires before you mount the fusebox but you can at least drill the holes you need and test fit it before getting too far into things.

    My next post will be where to route all these damn wires!
  19. Looks like I'm going to Lowe's this week, I need one of those!
  20. Is there room to mount the fuse block on the other side of the steering column? I have the same kit and was thinking of mounting it there, unfortunately I don't have anything mounted under my dash at the time to check for clearance. I think it would be easier to access in the future also.

    Sorry, just found your other thread.