GMC C3500 Back Up Light Switch Guide: 1979-1987 Models
Solving the common problem of reverse lights not working on your classic GMC C3500 truck.
- The switch location is different for automatic (on steering column) and manual (on transmission) models. You must buy the correct part.
- Always check the fuse and bulbs before assuming the switch is bad.
- For automatic transmissions, the new switch may require adjustment on the steering column to work correctly.
- Aftermarket brands like Standard Ignition and Rostra are the standard, reliable replacements as OEM parts are largely unavailable.
Is Your Back Up Light Switch Failing?
A faulty back up light switch is a common issue on these classic trucks. Before you buy a new part, always check the simple things first: make sure the reverse light bulbs are good and that the "TURN B/U" fuse is not blown. If those are fine, the switch is the next likely culprit. Problems often show up as flickering lights or lights that only work when you jiggle the shifter.
Common Failure Symptoms
- No Reverse Lights: The most frequent symptom. When you shift into reverse, the lights don't turn on at all.
- Intermittent or Flickering Lights: The lights flash on and off, or only work when the shifter is held in a specific spot. This often points to a worn or misaligned switch.
- Reverse Lights Stuck On: The switch can fail in the 'on' position, keeping your reverse lights illuminated even when you are not in reverse.
Choosing the Right Aftermarket Switch
For a vehicle of this age, original equipment (OEM) switches are generally discontinued or very difficult to source. The market is well-served by quality aftermarket replacements.
The most important factor is buying the correct switch for your transmission type.
- For Automatic Transmissions: You need the combination Neutral Safety / Back Up Light Switch. This is a larger, crescent-shaped part that mounts to the steering column under the dashboard.
- For Manual Transmissions: You need the screw-in style switch. This is a smaller, more compact part that threads into the side of the transmission.
Available Brands: Standard vs. Rostra
For the 1979-1987 C3500, you will likely encounter brands like Standard Ignition and Rostra Powertrain. Both are established aftermarket manufacturers.
- Standard Ignition (SMP): This is a very common and trusted brand in the repair community for this type of part. Their switches are widely available and are considered a reliable, direct-fit replacement.
- Rostra Powertrain: Rostra also produces a wide range of automotive electronic components, including switches, and markets them as meeting OE standards.
Pro Tip: Given the simplicity of this switch, both Standard and Rostra are considered good-quality choices. Your decision will likely come down to price and availability. There is no significant performance difference for this component on a C3500.
Back Up Light Switch Cost for 1979-1987 GMC C3500
| Part Type | Price Range |
|---|---|
| New Aftermarket (Standard, Rostra, etc.) | $16.17 - $26.63 |
| New OEM | Generally Discontinued |
| Shop Labor for Installation | $100 - $200 |
Frequently Asked Questions (FAQ)
Where is the back up light switch on my truck?
It depends on your transmission. If you have an automatic, it's part of the Neutral Safety Switch located on the steering column, inside the cab, near the firewall. If you have a manual 4-speed, it's a screw-in switch on the transmission itself, often on the driver's side.
My lights still don't work after replacing the switch. What now?
If a new switch doesn't solve the problem, you likely have a wiring issue. On a 35+ year-old truck, this is common. Check for power at the switch connector (light green wire is often for the back up lights). Inspect the wiring for breaks or corrosion, and check for bad grounds at the tail lights.
Can I replace the back up light switch myself?
Yes, this is a DIY-friendly job for most home mechanics. For automatic models, access under the dash is tight but manageable. For manual transmissions, you may need to access the switch from underneath the truck or by removing the transmission tunnel cover inside the cab, which is more involved. A special or modified 7/8" socket may be needed for the manual switch.
Does the new switch need to be adjusted?
For manual transmissions, no adjustment is needed. For automatic transmissions, the switch on the steering column is adjustable. If your lights work in Park but not Reverse (or vice-versa), the switch needs to be rotated slightly on the column until the lights activate only when the shifter is in Reverse. It's helpful to have a spotter watch the lights while you make small adjustments.
Technical Specifications
OEM Part Numbers: 14014559 14069600
Varies by transmission. Automatic: Crescent-shaped, multi-function switch on steering column. Manual: 2-terminal, screw-in plunger switch on transmission case.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.