JULY 15, 2025

Thieman TT15 Liftgate Hydraulic, Electrical, and Mechanical Components Explained

Whether you're a technician servicing a pickup truck liftgate or a distributor needing to identify replacement components, understanding the full mechanical, hydraulic, and electrical layout of the Thieman TT15 is essential. This guide explains how each system works together and provides verified references to help identify and maintain your liftgate for pickup truck applications.

• Documentation Resources from Thieman
• Hydraulic System Components: Pump, Cylinder, Hoses
• Electrical System: Toggle Switch, Circuit Breaker, Pendant Options
• Mechanical Structure: Lift Arms, Pivot Supports, and Bushings
• Control Switch Mounting and Location Options
• Circuit Protection and Grounding Best Practices
• Lubrication Points and Service Intervals
• Part Replacement Reference (How to Use Thieman Part Numbers)
• Conclusion

Documentation Resources from Thieman

Information in this article is sourced exclusively from Thieman's official TT15 series documentation. Always refer to your specific liftgate’s manuals for serial number, model, and vehicle-specific procedures.

Reference PDFs Used:

• Thieman Liftgate TT-15 Owners Manual
• Thieman Liftgate TT-15 Brochure
• Thieman Liftgate TT-15 Parts List & Owners Manual
• Thieman Liftgate TT-15 Installation Manual
• Thieman Liftgate Rear Camera Kit (KIT-235)
• Thieman Liftgate Remote Control Pendant (KIT-179)
• Thieman Liftgate Cab Cutoff Switch (KIT-131)

Hydraulic System Components: Pump, Cylinder, Hoses

The hydraulic system powers all lifting and lowering motions of the TT15, making it the heart of any hydraulic liftgate for pickup trucks. It includes a pump and cylinder assembly, fluid reservoir, and interconnected hoses.

• The pump assembly (P/N 4400871) integrates a 12V motor (P/N 4423520), breather, solenoid, and valves within a single compact unit located beneath the liftgate threshold (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 13).
• The cylinder assembly (P/N 4293) includes two hydraulic cylinders responsible for raising and lowering the platform. Each cylinder connects via 41" hoses and 57" steel tubes with MJ-MAORB restrictor elbows and tees for pressure management.
• Routine checks include monitoring oil levels, which should be within ½" of the reservoir top when the platform is fully lowered. Acceptable fluids include Dexron VI, Mobil 1 Synthetic ATF, and others listed in the fluid chart (pg. 10).

Hydraulic maintenance includes inspecting for leaks, checking relief valve pressure (set at 2300 PSI), and ensuring all components stay cool during operation (pgs. 10, 13).

Electrical System: Toggle Switch, Circuit Breaker, Pendant Options

The TT15’s electrical system activates the pump and solenoid valves for raising or lowering the lift. Core components include:

• Molded Toggle Switch Assembly (P/N 31446): This sealed, dash-mounted switch is the standard control point for liftgate motion (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 14).
• Circuit Breaker (P/N 4301770): Installed within two feet of the vehicle’s battery, it protects the electrical system from overload (thieman-liftgate-installation-TT15-INST.pdf, pg. 11).
• Remote Pendant Options: Kit 179 includes a 10-foot coiled cord pendant for secondary or remote operation. Both gravity-down (P/N 4309) and power-down (P/N 4310) variants are available (thieman-liftgate-remote-control-pendant-KIT-179.pdf).

Proper cable grounding and voltage (12.5V at rest, ≥10V under load) is critical for system performance. Corroded terminals or low battery voltage can cause slow operation or complete failure (owners manual, pg. 29–31).

Mechanical Structure: Lift Arms, Pivot Supports, and Bushings

The TT15’s structural integrity comes from its mechanical framework, which includes lift arms, idler arms, and pivot supports.

• The lift arm assemblies (LH: P/N 31356-001, RH: P/N 31356-002) and idler arm assembly (P/N 31302) connect the frame to the platform, allowing for pivoting motion during lifts (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 14).
• All arms and supports utilize replaceable bushings (P/N 5504-001) at stress points to reduce wear. Thieman specifies that if the gap between a pin and bushing exceeds 1/32", the bushing should be replaced (pg. 9).
• Pivot supports (P/Ns 31301-002 LH and 31300-002 RH) bolt to the truck and form the hinge point for the liftgate’s movement.

These components collectively stabilize the liftgate during operation, especially important when using the TT15 as a pickup truck tailgate lift.

Control Switch Mounting and Location Options

By default, Thieman made this TT15 liftgate to include a molded toggle switch assembly (P/N 31446) that mounts directly to the frame of the liftgate for easy access near the platform (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 14). This weather-sealed switch offers reliable operation for both raising and lowering the platform.

For users who prefer more flexibility, remote pendant controls are available through Thieman’s KIT 179. This kit includes a 10-foot coiled cord pendant, a receptacle, and a secondary control cord to enable either primary or secondary use (thieman-liftgate-remote-control-pendant-KIT-179.pdf). It's ideal for operators who want to control the pickup liftgate from inside the truck bed or while standing safely beside the platform.

Choosing between fixed and remote control depends on workflow. Remote pendants reduce the need to reach under the bed or walk back and forth to the toggle switch—especially useful in frequent load/unload scenarios.

Circuit Protection and Grounding Best Practices

Electrical integrity is critical to the safe operation of any hydraulic liftgate for pickup trucks, and the TT15 includes specific protections to ensure long-term reliability. Thieman recommends installing the included 150-amp circuit breaker within two feet of the truck battery. This breaker protects the motor and solenoids from overcurrent situations, especially during heavy load cycles (thieman-liftgate-installation-TT15-INST.pdf, pg. 11).

Equally important is proper grounding. The TT15’s hydraulic pump motor must be grounded using a #2 gauge cable bolted directly to bare metal on the vehicle frame. Poor grounding or thin wire can result in voltage drops, which may lead to motor overheating, slow lift times, or complete failure to raise or lower the platform (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 29–30).

Thieman specifies a minimum of 12.5V at rest and at least 10V under load to operate the pump motor effectively. If you're wiring a pickup truck with liftgate integration, verifying ground paths and voltage with a multimeter during installation is strongly recommended.

Lubrication Points and Service Intervals

The TT15 requires minimal lubrication, but key points still need regular attention for optimal function and longevity.

• Extension pivots should be oiled every 50 lift cycles with SAE 10 to SAE 20 oil (thieman-liftgate-owners-manual-TT15-OM.pdf, pg. 10).
• Pump oil should be changed annually, and the reservoir level checked monthly.
• Note: The TT15 uses special bushings that do not require lubrication (pg. 10).

This limited maintenance schedule supports the TT15’s appeal as a low-maintenance pickup truck liftgate.

Part Replacement Reference (How to Use Thieman Part Numbers)

Ordering replacement parts for a pickup liftgate is made easier by Thieman’s structured parts list and identification system.

To order a part:

• Locate the serial number on the curbside mounting plate.
• Determine the quantity, approximate part number, and a clear description for what you’re looking for.
• Contact our Team to assist in finding the correct part number for your specific gate.

Part categories include:

• Electrical (e.g., solenoids, breakers)
• Hydraulic (e.g., cylinders, hoses)
• Mechanical (e.g., lift arms, pivot supports, bushings)

This method ensures accuracy when sourcing parts for liftgate repairs or replacements.

Conclusion

The Thieman TT15 integrates hydraulic, electrical, and mechanical systems into one robust and serviceable pickup truck lift gates on the market. From its dual-cylinder hydraulic lift design to its toggle and pendant controls, every part is engineered for reliability, ease of maintenance, and performance. For fleet owners, distributors, or independent operators, knowing these components makes it easier to diagnose issues and order correct replacements for your pickup truck liftgate.

Whether you're troubleshooting a hydraulic leak, replacing a pendant switch, or just looking for the right bushing part number, use the Thieman documentation and this guide to keep your TT15 operating safely and efficiently.