Mention it once and your buddies will suddenly be busy for the next three weeks. Wiring is the bane of existence for many gearheads; voltage, ohms, soldering, not to mention the miles of wire and all the sorting involved can be a real headache. Wiring gremlins (the trouble makers, not the AMC econobox) are one of the main reasons a project car gets sold unfinished, but it doesn’t have to be that way.
There are several wiring companies offering turn-key wiring kits that simplify the process of updating the wiring in your Mopar. Having worked with Painless Performance in the past it was a no-brainer. The Painless kits are well marked, pre-sorted and bundled and come with just about everything you need to do the job. One thing we really like about the Painless Performance kits is the way they are labeled. Each wire is printed with it’s number code and termination point, you don’t have to search a list of wire codes to figure it out. In addition to that, many of the systems that you must integrate, such as turn signals and head and taillight connectors are color matched to the factory colors. Mopar changed things on a regular basis, so not all cars will match, but it is really nice for the majority of years that do.
The Royal Scamp is not your typical muscle machine, it is a street\strip drag car, so much of the interior (ok, all of it) has been gutted to save weight, this means the dash, instrument panels and lighting have been removed. We needed a switch panel to make it easy and provide the extra switches for the cooling fans, fuel pumps and nitrous controls, so we ordered an 8-switch master panel from Painless as well. This panel gives us all the major circuits and negates the need for a key (the factory column key was busted long before we got the car). It also keeps the dash area clean and neat. To be legal on the track, we added a remote kill switch to the rear tail panel of the Scamp, which ties directly to the trunk-mounted Optima Red-Top battery.
The biggest problem with wiring a car is the mess. There are several hundred individual wires that must be bundled and organized, Painless takes the time to bundle the wires with zipties into several groups, but you need to keep it tidy, for that we keep a few boxes of Painless’ PowerBraid nylon flex-loom. This stuff is easy to use and looks great.
You will need the basic wiring tools for this job- quality wire crimpers (good ones, like Klein-brand, not those junk multi-stripper/crimps), good wire strippers and cutters (we use a Klein spring-loaded set), soldering gun, quality electrical tape (3M Super is good, don’t use the cheap junk), plenty of zipties (some are included, but you will need some bigger ones too), and your basic handtools. In most cases, you will also need a drill and few drill bits, a step-drill bit is the easiest for these tasks. It is also a good idea to have a multi-meter on hand for testing wires when integrating circuits.
The wiring harness we chose required a little compromise. We picked up the Painless Universal Mopar Muscle Car Harness (PN 10127), which is a well-designed kit that worked great. The only problem is that it did not provide any additional wires for extras like fuel pump, nitrous or other additional circuits. The Painless streetrod harnesses come with those circuits built it. The Mopar-specific harness uses factory color codes for lights and ignition, whereas the streetrod harnesses use either generic or GM color codes. In our situation, the Mopar harness worked out because we reused the factory headlight, taillight and turn-signal wires (as would most builders), but we had to re-purpose a few extra wires to provide juice to our extra circuits. The point is that you need to research the kits before you buy so that you can make the right decision. Tracing the factory wires is not difficult should you choose to use a more generic harness with all the extra circuits.
We wired the Scamp in about (3) 8-10 hour days. It takes a while to get each section routed, trimmed, terminated, loomed and finally installed. When wiring a car, you need to start from a central location and work your way out. We mounted the fuse box to the center of the firewall and then wired the switch panel, ignition, rear section (taillights, fuel pump, battery), then moved to the front of the car for the headlights and engine bay. You work in sections to break it down. Complete one task before moving on to another. This will do wonders for your sanity. Should you get stuck, the tech department at Painless is excellent. We had some questions about wiring the switch panel to the main harness, and they helped us out. If you take your time and follow the guidelines in the instructions, you will have your wiring panned out in no time.
01. Out of the box, the Painless kit is bundled in the pre-arranged sections. Before moving into the car, we divided each group to sections we knew we would need together, and coiled the wire. This makes it easier in the car.
02. The switch panels comes pre-wired and labeled for all the major functions, including start, ignition headlights and fuel pump. We repurposed one switch for nitrous arming.
03. First, the fuse-block was mounted to the center of the firewall, next to the stock location.
04. The engine and headlight group was run out of the original fuse-block hole, which was covered with this supplied aluminum plate. Don’t stress about the unprotected hole, these wires will be loomed with Powerbraid.
05. This is where most gearheads freak out. This is a mess of wire and it certainly looks daunting, but have no fear, it is much easier when you break it down in groups. We separated each group and tied it to the dash bar, keeping it separate for routing.
06. The switch panel mounts to the roof roll bar using hose clamps from the backside, then the wires run through it and the face panel installed. The wires will get covered and zip-tied to the roll bar down the driver side kick panel.
07. The corresponding wires, which include the ignition, lighting, fuel pump, nitrous and cooling fan wires were routed behind the column mount, to the dash bar and over to the switch plug. Do this before cutting any wires.
08. Several wires require connection to the same switch circuit. Here is a neat trick- strip back enough wire from the tip, then strip another section further down, but don’t remove the jacket all the way. Then the second exposed area is split as shown.
09. Insert the other wire(s) into the split and twist. Nice and neat.
10. Then solder the connection. You could use a crimp terminal, but that is messy and we had to a special terminal for the switch plug which was too small for more than one wire. Your solder connection should look like this, detailing the actual wire strands. If you have a big glob, then your solder joint is cold and not good.
11. The plug harness uses special terminals that require a delicate touch. Here, we crimped the end in our crimpers.
12. This is the result. It takes practice to get this right, and even then, it doesn’t always come out right.
13. The Painless Performance harnesses do not include any grounds, you have to ground each circuit on your own. The master switch harness was wired to a short ground lead which was screwed to the inner kick panel.
14. The pins were inserted to the plug and the two halves plugged to each other. Note how much better this looks with the Powerbraid.
15. The kit does not come with a factory-style column plug, and our harness was long gone, so we cut the plug and wired the harness to the column wiring using the factory color codes. Butt-crimps work great here.
16. Then we hid the wiring in the column mount.
17. Since we are not using a radio, heat\AC or any of those extras, there were a few extra switches and constant hot wires we didn’t need. Instead of cutting them short and capping them, we left them long, bundled them together and wired them up under the dash for future use, this way you won’t have to tap into another circuit and you will have a dedicated fuse in the fuse box.
18. We ran the main bundle of wires to the rear of the car and started wiring the taillights. Again, not factory terminal, but the taillight harness was in good shape, and this plug uses basic spade terminals. We color matched each color, incorporated the ground and moved on.
19. Since all of the wires are bundled together running to the back of the car, we had to separate a few. To keep it clean, the Y was taped up like this, keeping a factory look.
20. The master kill switch was installed in the rear tail pan of the car. In the event of an accident at the track, the safety crew can shut off the battery from the rest of the system. This runs inline with the battery’s positive side.
21. Inside the trunk, you can see the main power feed coming in (left) and the main feed going out (right) to the front of the car. The smaller lead coming off the out-post is the power feed for the fuel pump relay.
22. With the back end of the car wired, our attention moved to the engine bay. The factory head light wiring was in good shape, so we decided to keep it. That meant deciphering a few wires. We needed to clean the dirt and grease from the wires first.
23. Using the multi-meter set to continuity, we tested the wires to make sure the color codes matched the actual bulb function. One probe connects to the plug and the other probe is touched to the wire to be tested. The painless kit comes with new headlamp terminals, but this is easier and works great. All the colors matched.
24. Then we soldered each wire to the factory wire. We could have used crimps here, but soldering is cleaner and less prone to failure.
25. To finish up the wiring, the motor needs to be in the car, which next on the schedule. We installed a distribution block (to the left of the brake booster) for the battery feed. The large blue wire will connect to the starter, feeding power to the rest of the car. The nitrous solenoids, MSD ignition box and anything else that needs a battery connection will be wired to the block. All the grounds attach to the body. The engine will have a ground strap that connects it to the chassis. In the trunk, the Optima Battery is grounded directly to the body and to the roll cage. The other coiled wire you see here are the trigger wires for the nitrous, the gauge sending units and the alternator wires.
A life-long gearhead, Street Tech Magazine founder and editor Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 5 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced. You can follow Jefferson on Facebook (Jefferson Bryant), Twitter (71Buickfreak), and YouTube (RedDirtRodz).