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1957 Chevy Wiring Harness - Shockingly Painless

Installing Modern Wiring To Handle Your Classic Bow Tie's Electrics Is Easy Thanks To Painless Performance.

Patrick Hill Jul 1, 2009

The Painless kit comes in a nice, neat bundle, and includes pretty much everything you need for installation except for crimpers and wire cutters. It's always good, though, to have some extra electrical terminals, tape, and shrink tubing handy.

Thanks to the aftermarket, you can equip your classic Chevy with all sorts of modern performance and luxury items that'll make an old car feel like a newer one. From modern fuel injection, to power windows, to high-tech stereo systems, pretty much any option you can find on a new car, you can install on an old one.

The problem is, the old factory wiring harnesses of the classic cars were never meant to handle the electrical load of modern accessories, or the sheer number of them. It's the same thing as having 12 different appliances in your kitchen, but only one outlet to plug them into. Even if you add ways to plug more accessories into your original wiring harness, it won't be long before the electrical load of all the modern equipment will melt the factory harness, and possibly turn the car into a fireball.

But the same aftermarket that's brought you all the high tech stuff to equip your Chevy also has the solution, a modern wiring harness capable of handling just about anything, with plenty of accessory hookups so you can customize and equip your old car with anything you're thinking about.


To make the job easier, both the front and rear seats were removed from the car. The back seat must come out so you can access the wiring going to the trunk.

Our project '57 was a prime candidate for an improved, 21st century wiring harness. After having a Classic Instruments gauge upgrade, an MSD-6 ignition box, and electric fans added, the factory '57 wiring harness (although fairly new from the car's earlier restoration) couldn't handle the power windows and stereo upgrades the car was slated for. So, we called the electrical gurus at Painless Performance to get one of their Tri-Five 18-circuit wiring harness kits.

A few weeks later, Painless founder Dennis Overholser showed up at our door with the kit we needed and his tools to help us install the harness. Dennis founded Painless Performance in 1990 (then Perfect Performance Products) to handle the needs of street rodders who were installing modern parts on older cars looking for a reliable wiring harness that was easy to install. From there the company took off, becoming one of the leading suppliers of aftermarket harnesses to the hobby.

Dennis took one look at the sorry state of the wiring in our '57, and knew he had his work cut out for him. Follow along as we upgrade the wiring in our hardtop.


With the cluster loose, Dennis cut off the wires leading to the gauges, leaving enough length to connect the gauges to the new harness. One helpful tip: Use a piece of tape to mark what wires serve which gauge on the cluster, just in case you forget or get confused.

After pulling the cluster, we found this surprise. This is the kind of thing that leads to dead shorts in a wiring harness, or worse yet, fire.

Taking a break to rest his back, Dennis moved into the engine compartment. We pulled the hood off for easier access to the firewall. The wiring in the engine bay was a mess too, so it all needed to be removed for the new Painless wiring.

In an engine compartment, messy wiring not only creates fire dangers, but can be frustrating when your car has an electrical problem and you can't diagnose what's going wrong. If you add anything like an aftermarket ignition, or other engine accessories, you'll play hell trying to get them wired up correctly.


The fuse block in the Painless kit mounts in the same location as the stock unit, using this bracket. Two screws and it's ready to go.

Before mounting the fuse block, it's best to uncoil the whole wiring harness, and separate the wiring bundles for the dash, rear of the car, and engine compartment. To make things easy on yourself, route the engine wiring through the hole on the firewall before you mount the fuse block.

Here you can see the fuse block mounted, and wiring routed to the dash and engine. At this stage it's hard not to look at the massive amount of wiring and lose your head. Don't sweat it. This job looks a lot scarier than it really is. Your best tool for the install is going to be patience, and organization. Think of it as a jigsaw puzzle you're just starting. At first there are a lot of pieces, but once you get going things get easier.

This is what makes installing a Painless wiring harness painless. Each wire is marked for where it needs to go and hook up to. Unless you've forgotten how to read (or are a three-thumbed editorial director), it's nearly impossible to screw up.

The wiring for the back of the car uses the factory wiring channel for routing. To get to this, you have to remove the sill plate then peel back the carpeting. The channel cover is held on by a few screws. Before laying the new wiring, you'll probably need to vacuum out decade's worth of crud from the channel.

When the wiring comes out of the channel, it goes through this hole concealed behind the armrest.

To make routing the wiring easier, we wrapped some masking tape around the bundles. This is all the wiring for the trunk, including speaker wires. The Painless harness gives you wiring for other accessories that could be in the trunk/rear area, like trunk lights, CD changers, power antennas, etc. If you're not going to use those particular wires, you can cap them off and hide them under the trunk mat, in case you want to add anything later on.


Again, this can look really overwhelming, but because everything's marked, you just have to sort through the wires, and route them to their destinations. This bundle you're looking at is everything for the dash. First route the wires in groups to their switches, then from there take it one wire at a time to trim and hook up using blade connectors. Again, patience is your best tool for this install.

Back in the engine compartment, it was time to start routing wires to the right places. We used a lot of the factory wiring clips and routes to install the harness, but also rerouted some of the wires for a cleaner look. Painless sells some really nice split braided loom material, so once you're done hooking everything up you can wrap the wire bundles to give the engine compartment a clean, organized look.

The car's factory air ducts coming from the headlights had been removed during the CAA A/C install, so the MSD box was mounted in this cubby hole. We routed the driver's side headlight and turn signal wiring along here to tuck it out of the way instead of using the factory wiring clips along the inner wheelwell.

Out back, it was time to hook up the taillights, back up lights, and license plate light. The wires for the back of the car also have the wiring necessary for a rear mounted electric fuel pump, so if your car has one, wiring it in is a snap.


Here's the finished trunk area. All the lights are wired up, and unless you really dig deep, you have no idea this '57 has fully modernized wiring.

For the wiring we weren't using in the trunk, we capped off the wire ends then coiled them up and tucked them into this channel for easy access later if necessary.

Here you can see where we used the factory locations to route the engine compartment wiring. Be careful when bending back the factory wiring tabs, after 50 years they can be brittle and break. After we had everything cut and plugged in, we went back and used Painless' special split braided sleeving to clean up the harness and conceal all the wiring in the engine compartment.

To make removing the gauge cluster easier, and clean up the wiring, Dennis hooked everything through a master plug, so if the cluster has to come out again in the future, just unplug the whole unit, remove the screws, and out it comes. This also cleans up the wiring behind the dash substantially so you don't have a hidden rat's nest of chaos.

The master power fuse for the whole harness mounts on the firewall. So you don't drain the battery, or for security, you can pull the master fuse and the car will be stone dead--no power to anything.

Here you can see how the Painless wiring hooked right into the factory dimmer switch. On the dimmer and ignition switches, having a factory diagram for wire locations on the switches will be necessary so you have everything hooked up correctly.

One of the tabs on our ignition switch broke while we were wiring everything in, so we gave the folks at Classic Chevy International a call, and they sent us their factory replacement ignition switch, PN 25-05.


Progress being made--the ignition and headlight switches are back in place, along with the factory climate controls. Doesn't look as scary as it did before, does it?

Here's another shot of the new fuse block mounted next to the control block for our Classic Instruments gauges. The Painless harness hooked right into the Classic Instruments unit with no problems.

With the gauge cluster reinstalled, it's time to hook up the new radio.

Here's another shot of the new fuse block mounted next to the control block for our Classic Instruments gauges. The Painless harness hooked right into the Classic Instruments unit with no problems.

Because our '57 had been converted to LED taillights, we had to use a special flasher, which Painless sells. LED lights use very little power, a normal flasher won't work because the LEDs don't draw enough power.

While we had the dash apart, we installed a new Custom Auto Sound head unit and speaker system (watch for this install in a future issue). All the wires from the new harness for the radio were clearly marked; it was just a matter of crimping on some butt connectors and plugging everything in. When we turned the key the new radio and speakers worked great.

Here's the new head unit going in. The CAS unit fits right in the stock position, so there's no cutting of the dash. After this, we just had to tuck up some wires, clean up everything, and wrap any exposed wires in the split braided material, and the job was finished.


Custom Auto Sound



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