Rewiring a 1968 Mustang - How I Did It

Rewiring my 68 Mustang

Hi all, this is a brief summary of my rewiring extravaganza of my 1968 inline 6 Mustang (auto without AC). The intent is to help others who are trying to rewire their own classic car.

I do not have any mechanical background and no electrical engineering background everything I learned from forums and YouTube so just use this as a guide and do your own additional research. I have links below to videos and products I used. My diagrams are attached.

My Problem:

I purchased a tach and converted my amp meter to voltmeter with Rocketman. I wired both power wires to the voltage regulator on the instrument cluster. Which worked fine for a period until one day the smoke was released from the wires. It burned my black/green wire all the way back to the ignition switch splice.

My failed attempt:

I contemplated just splicing in my own wires but since I already had the under-dash wiring harness out of the car, I wanted to do something more and I always wanted to replace the fuse box. However, at this point I had no idea how the stock fuse box truly worked. After watching quite a few YouTube videos I decided to buy a premade wiring harness and redo the entire wiring. At first, I wanted the Ron Francis kit, it was fairly pricey at $600, but it looked solid and had good reviews on the forums. I then found Haywire, EZ Wire, and KwikWire. These are all cheaper options than Ron Francis. After more research I decided to go with EZ wire because it was the cheapest and I was going to have to figure out all the connections and routing anyway and the main drawback on EZ wire was the poor directions.

I also briefly considered American Autowire and Painless but those are the most expensive and AAW required special crimping tools.

The EZ wire harness came and I was quickly disappointed in the quality of the fuse panel. The wires seemed fine and had writing on them so knowing which way to go with them was easy enough. I was too excited to get started so I starting installing the kit. The first and major problem with this kit for the 68 Mustang was that the wires routed down out of the fuse box. The stock fuse box has the wires route upwards and then towards the instrument cluster. When I mounted the EZ wire fuse box in the same location as the stock fuse box all the wires came down towards the pedals. They were out of the way but it was a mess of wires going every which way and was not a clean install. However, I continued routing and making connections.

Another problem with the EZ wire kit is that it spliced together the light wires (parking, headlights, etc.) at odd locations so there was a lot of extra wire if I didn’t cut and recreate my own splices.

After a lot of connections, routing, and redoing mistakes I finally was able to start the car and drive it around. I was proud of that but did not like how everything was routed and looked at the fuse box. I thought I could do better.

More EZ wire problems: It does not come with a horn power wire from the light switch to the column switch. Also, it does not have a reverse light wire from the Neutral Safety Switch to the reverse lights.

THE RE-REWIRE

After all that hard work, I ripped it all out.

I drew my own wiring diagram, I have attached it to this post. This I had to change countless times but you can use it as a guide for your own use. This helped me understand the circuits and helped with routing the wires. Be sure to have a routing plan before you start. I drew and edited my diagram for weeks until I ordered anything for the re-rewire. I routed mine like how it came originally. Also once I was done with the diagram I sent it to FedEx to get it laminated so I could reference it while wiring. I also laminated the original wiring diagram as reference, both 11x17.

After watching this video many times, I decided to use this Eaton Bussman Fuse and Relay Block. It did take quite a bit of figuring on which fuse/relay block to get but as you can see in the attachment, I made this one work by having the fuse side get power from the battery and jump power to the relay side. This allows for the fuse side to be constant for the radio constant, ignition, light switch, courtesy lights, and brake lights. The relay side is switched power for the turn signals, radio power, heater, instrument cluster power, and wipers. I used a ground buss to ground the wires from the relays then connected that to the ground at the firewall.

Important note: the light switch has an internal circuit breaker for an extra layer of protection. The aftermarket kits, do not consider this and run additional wire back to the fuse block that is not required. I ran two wires from the constant tab on the light switch, one for the horn and one for the emergency flashers.

I ordered all my wire from Wire Barn, I went with 25’ 14awg with 10 colors, and I needed every bit of it. I also ordered 12awg for the ignition wire from the fuse box, 10awg from the solenoid + to the fuse block, and 8awg from the 1 wire alternator to the solenoid +.

Connections: This is the most fun part. The aftermarket kits typically do not allow for the reuse of the Ford connections. I ended up reusing my original column connector, light switch, wiper, and beam selector switch. It is easy enough to de-pin all of these connectors using my wife’s bobby pin. I then purchased the original connectors from Clips and Fasteners. 1 box of each:







When making brand new connections, I used weather pack connectors. I really like these and after some practice got good at making them. The best site I found for purchasing these was CustomConnectorKits. They had the best prices and free shipping after $25. I had to order here multiple times and it arrived at my house in 2-days (we are both in CA). The crimper for the weather pack can be used for all the terminals, even the ones from Clips and Fasteners, it just takes a bit of practice. I used this crimper for the butt connectors and ring terminals. I had a kit of heat shrink terminals, it worked fine but if I didn’t have them I would have used more solder filled crimp on terminals from McMaster.

Something that had me stumped for a while was splicing 2 wires or even 3 wires to 1 wire. I needed to do this in a few locations. 3 to 1 (grounds for front lights). 2 to 1 (ignition switch), turn signal indicators. I found these on McMaster. They made sure I had a great connection.

Also, at times I had to put two wires in one terminal. When I did that I would solder a bit to the connection to ensure it was secure. I would use a larger terminal like the 12awg ones to fit two 14awg wires in. Soldering is easy just watch this video.

I also had some solder filled heat shrink butt connectors I bought from Amazon a while ago. I used these at 1 to 1 wire connections for the ignition switch because I had them but I trust stuff from McMaster, although it costs more.

Try to make as many connections as possible on the bench. I did this by using a scrap piece of wire and routed it where I wanted it to go and then marked the length and then took it to the bench and cut the proper wire to length and then made the connection. For me it was important to have not too long of wires, it makes a messy look and is hard to loom.

Instrument Cluster: This was intimidating at first but it wasn’t so bad. I used two 5 pin weather pack connectors to be able to disconnect the cluster and I made all the connections on the bench. I re-used the Blue/Red light bulb wire because it had all those splices as well as the voltage reducer wire from the voltage regulator. For these wires I used 18awg wire and reused some of the boot connectors for the stock look.

Alternator: I purchased a 1-wire alternator, which is super easy. It is one wire from the alternator to the Solenoid + make sure the wire can handle the amps. I used an 8awg wire for my 100amp alternator.

Ignition Switch: This is fairly straight forward looking at the diagram. I used one of the 2 to 1 wire McMaster connectors to connect the brown wire and the pink wire to the coil +. You do need the brown wire from the solenoid otherwise you may burn out your ignition switches. The A terminal from the ignition switch turns on the relays at the fuse box.

I used a 14awg fusible link to protect the wire from the solenoid to the fuse box. I think there are better fuses than the fusible link but I had the fusible link already and didn't want to mount anything to the fender.

Sequence: I wired up the fuse box which was easy and fun, I then mounted it and routed and wired things in this order: 1. Ignition Switch, Column Switch, Light Switch, Beam Selector Switch, Front Light Connections, and Instrument Cluster was last.

Things I haven’t finished:

I haven’t wired the heater. I read it is simple but it is summer now and I didn’t want to get into the wiring for it but it is set up and ready to go when I am ready to tackle it.

The courtesy lights. I have a wire with a 1 pin connection ready to go I just haven’t wired them up yet.

TIPS:

In the 68 you can remove the under-dash harness and not touch the headlight harness, which I wasn’t sure was possible until I did it.

Try to remove the firewall grommets carefully if you can so you can reuse them. The headlight grommet (the one by the master cylinder) put up a fight and I cut the grommet. It is hard to get a replacement grommet, but I found one at McMaster that worked for me. (After trying many grommets).

I didn’t mess with anything in the rear of the car. There are 3 connections in the front that control everything in the back. There are two 2-pin connectors on the driver side. One for turn signals, the other for reverse and brake lights, you can re-use these connections with the column terminal pins or use weather pack connectors. The gas gauge connection was on the passenger side on my 68, right now I have a three pin weather pack for this ready for the dome light wiring and passenger courtesy light wiring.

I bought a label maker, at first, I thought I wouldn’t need it but I am already happy I bought it. I bought this one on amazon and got cheap 3rd party heat shrink, it worked fine. You only need ¼” for 14awg wire.

Get extra terminals for mistakes to prevent having to wait for another order to come in just cause you are a few terminals short.

Fuses are designed to protect the wire not the instrument. Use an amperage chart to see how many amps a length of wire can handle. If you have a 20’ length of 14awg wire, it can handle 20amps. So don’t have a fuse larger than 20.

Try not to cut wires. My under-dash got cut up pretty good but I was able to remove the headlight harness in tact, I may try to sell it to recoup some costs.

Use this video to understand switches.

COST: I spent $1,084 +/-. This includes the first kit and all the tools, small parts, and mistakes. For just the rewire after I figured it out, it cost just under $600 (includes label maker and a Milwaukee work light for under dash). Hopefully this post helps you do it right the first time and saves you some money. If you do go with an aftermarket kit know that you will likely need to purchase additional connections, loom, tools, etc.

If I can do it, you can do it.

Thanks for reading, if you see something wrong or something that could have been done differently, please reply.

Useful Links and My Photos