How to Wire a Leer Truck Cap: The Complete Guide

Installing wiring in your Leer truck cap can seem intimidating, but with the right guidance it can be a straightforward DIY project. Proper wiring allows you to power interior lights, electrical outlets, and other accessories that make your cap feel like a home away from home.

In this comprehensive guide, we’ll walk through all the steps needed to wire a Leer truck cap from start to finish. You’ll learn how to:

  • Choose the right wire gauge for your electrical needs
  • Safely run wiring from the truck cab to the cap
  • Install interior lights, outlets, and switches
  • Connect accessories like fans, heaters, and stereos
  • Fuse all circuits to prevent electrical fires
  • Keep wires tidy for a professional look

We’ll also share pro tips, materials lists, and step-by-step wiring diagrams to help you complete your truck cap wiring project with confidence. Let’s get started!

Key Takeaways for Wiring a Leer Truck Cap

Here are some of the most important things to keep in mind:

  • Use the proper gauge wire for expected electrical load. Heavier loads require thicker wire.
  • Don’t skimp on fuse protection – install fuses at the power source and circuits.
  • Carefully seal any holes drilled in the cap to prevent water leaks.
  • Keep wiring neat and secure with wire looms, zip ties and insulated staples.
  • Label all wire runs for easy identification and troubleshooting.
  • Have a plan before starting – draw a wiring diagram to visualize the layout.

Step 1: Determine Your Electrical Needs

The first step is deciding what type of wiring and how much of it you’ll need. Consider what accessories and features you want to install now and might add down the road. Some common truck cap electrical components include:

  • Interior Lights – Dome/reading lights, strip lighting, remote switchable lights
  • Outlets – 12V and 120V outlets for powering electronics and appliances
  • Fans & Heaters – For climate control and circulation
  • Audio System – Speakers, amplifier, head unit
  • TV/Computer – For entertainment or work on the go
  • Refrigerator – 12V DC refrigerator/cooler
  • Battery Charger – For maintaining house batteries

Make a list of everything you want to power in the cap. Then determine the voltage (12V DC or 120V AC), wattage or amp draw of each item. This will tell you the total electrical load that must be supplied.

As a rule of thumb, plan for at least 20% more capacity than you need for future expansion.

Step 2: Choose Appropriate Wire Gauges

Selecting the proper wire gauge (thickness) is critical for safety and performance. Thicker wires allow more electrical current to flow with less voltage drop.

Here are the recommended gauges for various amperage draws in a 12V DC truck cap system:

  • 15-20 Amps – Use 14 AWG wire
  • 20-30 Amps – Use 12 AWG wire
  • 30-50 Amps – Use 10 AWG wire
  • 50-70 Amps – Use 8 AWG wire
  • 70-100 Amps – Use 6 AWG wire

For 120V AC circuits, follow the electrical code requirements for appropriate wire sizes based on breaker amp ratings.

In general, it’s better to err on the side of a thicker wire gauge, especially for long wire runs. This avoids issues with wires overheating or excessive voltage drop.

Step 3: Run Power Source Wiring

Now it’s time to run the main power wires from the truck cab to the cap. This provides power to everything downstream.

There are two options for tapping into vehicle power:

Option 1: Tap Into Truck’s Electrical System

This method runs wires directly from the truck’s battery to the cap. It requires drilling a hole in the truck bed.

Locate a spot that avoids debris, heat sources, and moving parts. A common location is through the front of the truck bed, near the cab.

Use a hole saw to cut a clean hole just large enough for wires to fit through. Rubber grommets will protect the wires from abrasion.

Be sure to seal the hole to prevent gas/fumes from entering cab and moisture from damaging truck wiring. Silicone or outdoor sealant works well.

With the wiring hole created, run 2 power wires through:

  • Positive Lead – Red 10 AWG wire from truck battery positive terminal
  • Negative/Ground Lead – Black 10 AWG wire from truck battery negative terminal

Attach using crimp connectors or solder and heat shrink tubing for a reliable connection.

Adding an in-line fuse holder with 60A fuse protects the circuit from shorts. Mount it under the hood within 18 inches of the battery.

Option 2: Install Auxiliary Battery

For a self-contained electrical system, you can install a dedicated auxiliary battery in the truck cap instead.

Common types are deep cycle RV/marine batteries or absorbed glass mat (AGM) batteries. Choose one with appropriate capacity for your total load.

Mount the auxiliary battery in a secure, ventilated area. Run heavy 10 AWG positive and negative leads through to the cap interior to distribute power.

Put a battery isolator on the positive lead under the hood. This allows charging from the truck alternator while keeping the two battery banks separate.

With either option, use wire sheathing, looms, and grommets to protect against chafing. Make sure to seal all exterior holes.

Step 4: Distribute Power in the Cap

Once the main supply wires are run into the cap, you can start wiring the sub-circuits for lights, outlets, and accessories.

First, determine mounting locations for components and plan wiring routes. Position items like lights, switches, and fixtures where they are most functional and visually appealing.

Power Distribution Block

Install a power distribution block to split the main power feed into multiple outputs.

This allows you to run a single 10 AWG supply line from front to rear of cap. Then use smaller 14 AWG wires for individual branch circuits.

Choose a power block rated for at least 60A total current. Leave space around it for additional circuits later.

Bus Bar Panel

For more circuits, a bus bar panel offers greater capacity and flexibility. Bus bars allow neat branch connections using terminal lugs.

Choose a bus bar rated for 100-200A total load. Install it on a non-conductive surface like wood or plastic.

Label the bus bars clearly as positive and negative to avoid polarity mistakes.

Step 5: Wire Interior Lights

Let’s start wiring some circuits! Interior lighting is essential for working, camping and changing clothes in your cap.

Small dome lights typically draw 1-2A each. For general illumination, space 4-6 lights throughout the cap interior.

Use narrow gauge 18 AWG wire to connect lights in a “daisy chain” from the distribution block. Don’t exceed 10 lights per circuit.

Install rocker switches by each entry door to control groups of lights. Use 14 AWG wire runs.

LED strip lights add a nice glow for mood lighting. Keep strips short (<5 feet) and use 18 AWG supply wire. Connect with crimp terminals or solder.

For task lighting, install swivel reading lamps above the bed or dinette. Use a small switch at each location to control the light.

Finally, choose warm 2700K or 3000K bulbs to avoid harsh glare. Dimmer switches create great ambiance.

Step 6: Add Switches and Wiring

Switches enable safe and convenient control of all your truck cap’s electrical components.

  • Mount switches in intuitive, easy to reach spots. Panel by the door is most common.
  • Use weatherproof switches for exterior lights.
  • SPST switches work for simple on/off control.
  • DPDT switches allow switching power from multiple sources.
  • Use diagram to organize switches logically. Label each.

Choose switch rated for appropriate voltage and current. For general lighting, 15A/12V switches are ideal.

Use 14 AWG wire to connect switches to lights, fans, and other loads. Run power supply wire to a distribution block first, then out to switches.

Make sure to size wires for the total load of all items a switch controls. Place fuses at power supply ends.

Step 7: Install 12V Power Outlets

12V DC power outlets allow you to plug in and charge phones, laptops, cooler, vacuum, or other gadgets.

  • Put outlets by bed, at workstation, and near entry door.
  • Use 15A single receptacle outlets. 20A dual outlet if you need more capacity.
  • Wire with 14 AWG from distribution block through 15A fuse.
  • Label positive and negative outlet terminals to ensure proper polarity.
  • Mount outlets in enclosure box for flush, secure fit.

Tip: Include a dual USB charging port for convenient phone charging. This only requires thin 22 AWG supply wire.

Step 8: Wire Exterior Lights

Exterior lighting makes your truck cap functional for loading/unloading in the dark, as well as looking sharp.

Marker/clearance lights illuminate cap sides and outline. Use small 18 AWG wire to connect individual LED pods.

Scene lights mounted high on each side provide flood lighting. Use 12 AWG wire and 60W max load per light.

For the rear, install a license plate light plus tail/brake lights for road visibility. Use 14 AWG automotive primary wire.

Auxiliary reverse lights are extremely helpful for backing up in the dark. Use 12 AWG wire to handle power draw.

Don’t forget small step lights at doors to safely enter/exit. Use dimmable LEDs and 18 AWG wire.

Finally, protect all wiring with conduit running underneath cap exterior.

Step 9: Install 120V AC Convenience Outlets

Having 120V AC power enables you to run appliances and power tools just like at home.

But feeding 120V AC into a truck cap requires extreme caution and knowledge of electrical codes and practices. Consider hiring an electrician for this part of the project.

With proper permits and materials, here is how to wire 120V AC outlets:

  • Use heavy 12 AWG 3-conductor cable (hot, neutral, ground)
  • Shut off shore power source before wiring
  • Install GFCI outlet for safety near water sources
  • Use water-tight exterior outlet covers
  • Label hot vs. neutral wires correctly
  • Match polarity in outlets across all circuits
  • Connect to dedicated 30A circuit breaker
  • Include 4A Edison fuse for overload protection
  • Place outlets above flood level
  • Use ground fault interrupter fuse for shock prevention

Regularly inspect all 120V AC wiring for damage, cuts, or loose terminals. Having an annual electrical inspection performed is wise.

Step 10: Install Fans, Heaters and Accessories

The finishing touches involve wiring convenient accessories like fans, heaters, stereos and fridges.

Fans circulate air and keep condensation down. Use 14 AWG wire for most models drawing 5-10A.

Small space heaters and cooling units liven up chilly nights or hot days. Consult wattage rating and use appropriate 10-12 AWG supply wire.

For your audiophiles, an amplified stereo system will get the tunes pumping. Use thick 10 AWG wire for powering subwoofers.

Keep food and drinks chilled with a handy 12V refrigerator wired with 14 AWG cord. Get the larger 3-way models to tap into 120V AC or propane too.

With some thoughtful planning, even large accessories like a TV, microwave, or coffeemaker can be wired safely. Just be diligent about load capacities and follow all electrical guidelines.

Step 11: Install Fuses for Safety

Fuses are incredibly important for preventing fires from electrical shorts or overloads.

Install blade fuses at the power source, distribution blocks, and any high-draw components:

  • Use 60A fuse max at battery connection
  • 15A fuses for lighting circuits
  • 20-30A for outlets and fans
  • Match fuse amperage to device load
  • Use slow-blow fuses for motors

For 120V AC circuits, install code-approved breaker panel with labeled circuit breakers instead of fuses.

Implementing proper fuse protection gives you peace of mind that electrical issues won’t put your truck cap at risk.

Step 12: Neatly Route and Secure Wires

The final step is neatly routing all wires and securing them safely in place. A clean electrical layout looks professional, is easy to service, and avoids hazards.

  • Use flexible wire loom or spiral wrap to group wire bundles entering the cap. Secure with adhesive mounts.
  • Route wires neatly along edges and structural surfaces. Avoid high-traffic areas.
  • Use insulated staples or zip ties to fasten wires every 12-18 inches.
  • Connect wires to terminals or blocks securely using crimp, solder, or set screw connectors. No loose strands.
  • Provide a 6-inch service loop at connection points for easy servicing.
  • Label wire runs using printed tags for future reference.
  • Caulk around all interior and exterior holes with silicone sealant.
  • Double check polarity, tight connections, and fuse positions.

Proper wire routing takes some time but really finishes off your electrical project.

Wiring a Leer Truck Cap: Final Checklist

  1. Assess total electrical load and wire gauge needs
  2. Run supply wires through sealed hole into truck cap
  3. Install distribution block and wire branch circuits
  4. Add interior dome lights and switches
  5. Install 12V outlets and USB charging ports
  6. Wire exterior clearance lights, reverse lights and scene lights
  7. Add 120V AC convenience outlets if desired
  8. Install and wire fans, heaters, fridge, stereo
  9. Fuse all circuits appropriately
  10. Neatly route and secure wiring using loom, zip ties and labels
  11. Seal all holes with silicone caulk
  12. Verify polarity, security and fuse positions
  13. Test each circuit and accessory
  14. Drive and enjoy your fully wired Leer truck cap!

Following this comprehensive 12-step guide will help you complete your truck cap wiring project with greater understanding, safety, and enjoyment. Take it slow, be diligent about electrical codes, and don’t be afraid to call in a professional electrician if needed.

We hope these wiring details give you the confidence to DIY your Leer cap installation. Now the fun begins customizing your mobile adventure base to match your needs and style. The electrical system is what brings everything to life, from lights to tunes to power outlets.

Drive safe and let the open road take you wherever you want to go!

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