I am trying to finish the rear end, roll bar, and floor pan and underbelly makeover of my Mustang. As I put it back together, I am also trying to clean up some of the less than desirable work done by the original builder. The car was built and campaigned as a bracket car in Louisiana, so a lot of the mods done to the car were good in concept, but poorly fabricated, in example – relocating the battery to the trunk.
The builder stuck it back there, made a home made tin pan for the battery which resulted in rusting the trunk floor, and routed the cables willy nilly, with little thought to fire or proper grounding. I also wanted to clean up my fuel pump wiring as well so I knocked out a lot of this mess in one project.
I had already replaced the trunk floor pan where the battery had been, and I opted to keep it there. I started this project with a Optima Red (no bad juices to leak) and a Jeg’s battery box. I went to a local big truck supplier and picked up 18 feet of 4ga red cable and had lugs swedged on both ends along with 12 ga pig tails for power take off. I also bought a 30 in 4ga ground wire, and a 24 inch 4 ga positive wire to go from the battery to the kill switch. I bought a Jeg's heavy duty alternator wire kit as I had converted to a one wire Alternator; I also picked up a couple of the heavy 50 amp fuse kits. You don’t have to have it, but a master disconnect switch is highly recommended and really nice to have when your working on the electrical system, you can isolate the whole car with a flip of the switch, it is also required as a master kill switch at most tracks.
The tools are pretty basic; drill, stepped bit for drilling holes, grommet kit, heat shrink tube, heat gun (I found my Wagner paint stripper is better than butane torches, takes bit longer and does have residual heat, but it doesn’t discolor the wire), wire terminal kit and pliers, basic shop tools (hammer, vice wrenches etc).
First thing, locate where your want your battery, based on weight distribution, cable run, accessibility etc. I chose to place mine on the passenger side trunk floor because the kill switch was already located through the right taillight panel, also I wanted to run the cable up the passenger side to the regulator, and its closer to where my fuel pump is mounted. Also, there is more room on the passenger side than driver side due to gas tank/drive shaft offset.
I placed the battery box in the area I wanted it, then used the battery hold down bracket to locate where to drill the holes in the trunk floor and battery box. Be sure your holes straddle your rear frame rail, its close in there.
Drill out your 5/8s holes in your trunk floor and box bottom for your all thread, and then be sure they fit. Now its time to mount the retainer box and rods to the car! Rather than putting some nuts on the bottom and top, and cranking it down, I wanted to spread the load on the rods, battery and car, and be sure when I removed the battery the rods stayed in place.
I used large fender washers on the inside of the box, and underneath the car, note how I bent the washers over to conform to the box and frame rails to spread the load. I then added jam nuts to ensure the main nuts stayed in place. I just hand tightened these for now to mock up the fit. The height of the rods is important, and I had an ulterior motive. I wanted to set their height with the battery top and bar, but also use a couple of nuts and jam nuts properly adjusted, so when I tightened down the cross bar, the bar would tighten up on the battery but bottom out on the upper nuts. This keeps the battery good and tight while preventing excess pull on the floor pans and preventing excess crush from the battery cross bar on the battery top.
I placed the battery in the box, and laid the cross bar over it (note the hold down doesn’t fit down and over the Optima, so I flipped it over, I probably will have to fab up a new hold down bar later) then I ran the rods down until I only had a inch or so of rod over the battery hold down bar. Once this height was set, I pulled the battery, and cranked down the nuts from underneath. The bent washers keep the nuts from spinning inside. I then set the jam nuts inside and out. I put the battery back in, put the cross bar on and tightened it down good and snug, then ran the upper nuts up to the hold down bar and set the jam nuts. Now it’s all locked in, you can remove the battery bar without the rods spinning, and the bar doesn’t crush your battery.
Now to run the cables! I am also running my alternator wire to the battery with the cable so I had two wires to run, the 4 ga battery wire and the 8 ga alternator wire. I laid both out on the floor and taped them together to keep it easy and clean, as you bend the cables around you will have to cut the tape to allow for different radius, and re-tape them.
I went a different route from the trunk to the engine bay, there are numerous possibilities, I chose the direct route that didn’t clutter up my frame rails or require a bunch of holes in my new floor pans, or require messing around the front springs and suspension. I ran the positive cable/Alt wire along the trunk floor across the rear end/shock pan into the passenger compartment. I notched a corner of my rear seat metal divider to ensure clearance.
From there I tried to follow the grooves in the floor pans up to the seat bases, where I drilled holes in the front and rear of the bases for the cable to pass through, continuing up along the toe board to the fire wall, next to where the heater motor would be (I don’t have one, but I ensured I left room to re-install it if I wanted to). Passing the wires through the fire wall can be done with a stepped drill, grommets and heat shrink or you can buy a firewall lug. I chose the hole/grommet method.
Once through the firewall, I routed the cables along the fender aprons to the regulator.
The trick here is to remember as you run the wires, and pass over or through holes, edges etc slip your grommets over the wires at that point, you can’t wait until its all in, and otherwise you won’t be able to work the grommet back. Also, don’t just measure and drill for the wire size, you have to get the end eye or connector and larger shrink wrap through the hole as well.
Working back from the regulator, I left enough slack to ensure I could connect the wires to the solenoid and alternator with enough of a coil to allow for vibration dampening, then started pulling the wires fairly tight, and attaching it to the firewall using insulated cable hangers attached to the shock tower bolts. When I came to the firewall, I not only installed the appropriate size grommet, I also marked on the wires where they passed through the firewall and slid a piece of heat shrink over the mark, and melted it on for added protection.
I worked the wires down the toe board, using existing recesses in the floor to minimize the wire “hump” under the carpet, back to the seat base. When I drilled the seat bases, I didn’t want any lip sticking up on the wire, so I drilled the holes, and then ground the lower lip even with the floor, so the wires laid flat, no sharp edges. This precluded use of grommets, so here I sliced open a shrink sleeve, wrapped it around the wires and slid it into the hole, zip tied it, and heated it to shrink in place.
Now, look at your battery posts and their relationship to your wire run and kill switch so you can access your box, run your ground and positive wires to your switch and keep it all clean.
Now to hook it all up! My positive main cable wire had been pre terminated with lugs and shrink wrap at the suppliers, but my alternator wire had to be lugged and sealed. I chose to use one of the 50amp fuse blocks to protect the charging system. I mounted the fuse block on the battery box, and measured and cut my alternator wire to come up to the fuse block, then installed weather proof heat shrink eyes. In order for the kill switch to actually stop your car from running, the alternator has to go to the battery side of the kill switch, so I installed a larger lug and heat shrink from the fuse block to the battery or off side of the kills switch. I ran the main positive battery wire from the engine compartment to the on side of the kill switch, and ran my 24 inch battery wire from the battery (I eyeballed it, don’t hook it up to the battery yet) to the off side of the kill switch, now the car will be electrically isolated when in the off position..
Moving to the front, I connected my battery wire to the battery side of the regulator (side opposite your starter lead) taped and sealed the pigtail since I am not using it yet, and I installed a lug and heat shrink on my Alternator wire. I left enough slack in the wires to form a loop on the Alternator to prevent vibration from loosing the lug, something I have learned from electricians on the ships.
I used a 30 inch 4 ga ground wire, and ran my ground wire off the post (eyeballing it, not hooked up yet) straight down the forward edge of the box, through the trunk floor and attached it too the tie down bracket bolt on the frame rail, ensuring it was insulated with a grommet as it passed through the floor.
Now you can install your positive terminal to your battery, and then your negative terminal. Your power is all hooked up, insulated and isolated!
I went a little further in this project with my fuel pump wires. What a mess! Having read some great articles on electrical systems from FATNFAST , I would like to go there, but I only have one electrical device now so I stuck with the basics of keeping the fuel pump relay close to the pump, and running a switch wire to the cockpit switch.
I chose to pull power off the battery and run it forward to the cockpit so I had a hot battery feed up there for future use.
To do this safely I used the second 50 amp fuse block, and pulled a hot wire off the off side pigtail of the battery cable, mounted the fuse block on the opposite side of the box. I then phished the main power wire, fuel pump switch wire over the passenger wheel well, down under all of the rear quarter window mechanisms (feel around in there, there is a gap or bracket you can go under) and out into the rocker channel, from there it runs up into the passenger compartment where it exits over the kick panel, then over to my switch panel. I covered this all with wire tube covering.
To keep it clean an orderly, I fabricated a bracket out of a piece of stainless steel to mount my regulator and circuit breaker. I then ran my fuel pump power wire off the relay (painless relays are well marked for this) through the factory grommet for the factory fuel gauge sending unit. Drill a small hole through the factory wire bushing/grommet, being careful not to nick the sending unit wire.
I plugged my fuel pump in with quick disconnects, grounded it, connected the switch and power wires to a switch panel. I closed my eyes, hit the master switch, no arcs or sparks, flipped on the fuel pumps and heard the Holly Blue pump doing what it does best, make a lot of noise. Then I spun the engine over, it’s all good!
I had my wife help me with some “action shots”, this is the look I get, she does like helping, but she laughs at me a lot as well.
Hope this helps someone out, its one way of many. When I add more electrical items, I will re visit the power/fuse panel, for now it’s simple and too the point.
Be safe as always, and have fun!