Start with what is installed
Factory System Overview
The newer GMT800 Silverado and Sierra arrived for 1999, but the older GMT400 Classic continued alongside them. This guide is for the newer body style. Confirm the actual generation before using a model-year search to choose radio or speaker parts. The extended cab also came in different rear-door layouts, which changes where the rear speakers are reached.
Confirm original equipment
Front doors contain the main woofers, and the optional six-speaker system adds separate front-door tweeters. Rear 4x6-inch speakers sit in both rear doors on four-door trucks; the three-door arrangement places one in the rear door and the other behind side trim. The original analog OnStar system is no longer supported, so a new radio should not be presented as a way to restore that service.
Planning guide, not a fitment guarantee. Match wiring, impedance, adapters, fasteners and removal instructions to the actual vehicle. Photos illustrate selected configurations, not every trim level or every removal step.
Radio Upgrade
The GM AM/FM CD receiver is slightly taller and shallower than most single-DIN aftermarket radios. A single-DIN replacement uses the appropriate dash kit. A double-DIN conversion needs the correct replacement dash-panel kit and a check of the receiver’s depth and support clearance. Avoid assuming a flip-out screen will work: the column shifter can occupy the same space.
Installation planning
Use the correct antenna adapter and vehicle-specific harness rather than cutting the factory plugs. Remove the dash surround carefully and keep its clips organized. Confirm any optional control-retention needs against the actual truck and receiver. Once connected, test the receiver, all speaker channels and any retained functions before reinstalling the trim; a working display alone does not establish a complete installation.
Shop Speaker Sizes
Choose a location below, then browse the matching collection.
Front doors • 6.5-inch factory
6.5-inch coaxial speakersChoose the correct bracket and confirm depth.
Front doors • optional tweeters
Car tweetersDiameter is not specified. Secure custom mounting is needed.
Rear doors / side • 4x6-inch factory
4x6-inch coaxial speakersPosition depends on three- or four-door cab. New mounting holes are needed.
These collections are browsing categories, not vehicle-fitment guarantees. Check mounting depth, brackets, wiring, impedance and crossover requirements. Alternate sizes need the specified mounting adaptation. A coaxial speaker is not interchangeable with every component woofer or tweeter.
Speaker Locations
Front-door woofers are 6.5-inch units. A 5.25- or 6.5-inch replacement can use the appropriate adapter bracket, while a 6.75-inch option requires drilling and its own fit check. Removing the door trim gives access to the original mounting arrangement. If separate tweeters are present, plan a secure custom mount and a compatible crossover rather than assuming that a replacement tweeter clips straight in.
Rear speakers and access
Rear speakers are 4x6-inch units mounted on clip-in plates. Aftermarket installation requires new mounting holes. Smaller 3.5- or 4-inch speakers are alternatives with adapter brackets, but the grille shape alone does not confirm usable depth. Match the removal instructions to the three-door or four-door cab, and test the rear channels before closing the trim. Stop if the actual panel arrangement differs from the reference.
Tools
Have a panel tool, 7mm socket, ratchet and extension ready for the receiver and front-door work. Rear-speaker installation also calls for a cordless drill for the new mounting holes. Inspect the area behind each hole before drilling, wear eye protection and protect the interior from metal shavings. Keep location-specific screws and clips separate during disassembly.
Bass and Amplifier
The extended cab offers more placement choices than a regular cab, but rear seating and storage still determine the usable space. Measure a vehicle-specific enclosure or compact powered subwoofer against the actual seat arrangement, seat movement and cable clearance. A product described as truck-specific still needs an exact cab/year fit check. Secure the enclosure so it cannot shift under braking.
Build around the truck
Door sound treatment can address panel resonance and rattles while the trim is removed. Preserve drains, window movement and access to hardware rather than covering everything indiscriminately. If adding an amplifier, plan a protected, correctly fused power route and ventilation. Security and remote-start work should be matched to the truck’s wiring and safety interlocks by an experienced installer.
Installation Checklist
Complete the system in stages and check it again after reassembly.
- Confirm the year, generation, cab and factory equipment
- Choose a compatible radio kit, harness and antenna adapter
- Check all original functions that need to be retained
- Verify each speaker size, depth, bracket and electrical requirement
- Protect wiring and inspect behind every new mounting hole
- Test each channel and door function before refitting panels
- Secure added bass equipment without obstructing moving parts
- Check final operation after all trim is installed
Keep a record. Save equipment models, interface instructions, wiring changes and tuning settings for future service.
Car audio guides, upgrades and installation planning.
