GMC K1500 Back Up Light Switch Guide (1979-1987)
If your reverse lights are out, the back up light switch is the most likely culprit; here's how to choose the right replacement for your truck.
- The switch location is different for automatic (on steering column) vs. manual (on transmission) models.
- Failure is a safety issue, as it prevents others from knowing you are reversing.
- Always check bulbs and fuses before replacing the switch.
- If a new switch on a manual transmission doesn't work, the issue may be internal to the gearbox.
Is Your Back Up Light Switch Failing?
A bad back up light switch is more than an inconvenience; it's a safety issue. The most obvious sign of failure is when your reverse lights don't turn on at all. Before you assume the switch is bad, always check the fuse and the bulbs first. If the fuse and bulbs are good, the switch is the next logical part to inspect.
Key Failure Symptoms:
- No Reverse Lights: The most common symptom is that the reverse lights do not light up when the truck is put in reverse.
- Lights Stay On: Less common, but the switch can fail in the 'on' position, causing the reverse lights to stay on continuously, even when not in reverse.
- Intermittent Lights: The lights may flicker or only work when you wiggle the gear shifter. This points to a worn-out switch or a loose connection.
A Note on Manual Transmissions
For manual transmission models, it's possible for an internal part in the gearbox to wear down. This means the transmission no longer pushes the switch's plunger in, even if the switch itself is new and working. If a new switch doesn't solve the problem, this may be the issue.
Choosing the Right Aftermarket Switch
For a truck of this age, new OEM parts from GM are generally not available. The market consists almost entirely of new aftermarket parts. Brands like Standard Ignition and Rostra are common choices. In general, forum discussions about these trucks note that the quality of modern electronic replacement parts can be inconsistent, regardless of brand. However, both Standard and Rostra are established aftermarket manufacturers that produce parts to meet original specifications.
- Standard Ignition (SMP): A well-known aftermarket brand offering a wide range of automotive electrical parts. Often considered a reliable choice for replacement components.
- Rostra Powertrain: Another established manufacturer, known for transmission components and electronic parts.
When buying, the most critical factor is ensuring the part matches your truck's specific transmission (manual or automatic), as the switches are completely different.
Pro Tip: Diagnosis
If you have a manual transmission, you can easily test the circuit. Disconnect the two-wire plug from the switch on the transmission. Use a small piece of wire to connect the two terminals in the plug. If your reverse lights turn on, the circuit is good and the switch is bad.
Known Issues, Recalls, or TSBs
There are no known recalls or Technical Service Bulletins (TSBs) from the National Highway Traffic Safety Administration (NHTSA) for the back up light switch on the 1979-1987 GMC K1500. Any failures are typically due to normal wear and tear over the decades.
| Part Type | Price Range |
|---|---|
| New Aftermarket | $16 - $27 |
| Shop Labor | $90 - $150 |
Frequently Asked Questions
Where is the back up light switch located on my K1500?
It depends on your transmission. For automatic transmissions, it's part of the Neutral Safety Switch on the steering column, inside the cab near the firewall. For manual transmissions, it's a screw-in switch on the side of the transmission itself.
Can I replace the back up light switch myself?
Yes, this is a DIY-friendly job for most home mechanics. For manual transmission trucks, you'll need to safely get under the vehicle to access the switch on the transmission. For automatic trucks, you'll be working under the dashboard, which can be a tight space. The difficulty is low, typically taking less than an hour.
My new switch didn't fix the problem. Now what?
First, re-check the bulbs and the fuse. Then, check the wiring for breaks or corrosion, especially the ground wires. If you have a manual transmission, the problem could be an internal transmission issue where the shifter is no longer activating the switch plunger.
Do I need to drain the transmission fluid to change the switch?
No, you should not need to drain the transmission fluid. The switch is located high enough on the case that only a very small amount of fluid, if any, might seep out when you remove the old switch. Have the new switch ready to install quickly to minimize any loss.
Technical Specifications
Location and type are dependent on transmission. Automatic transmission switches are part of the Neutral Safety Switch assembly on the steering column. Manual transmission switches are typically a 2-prong, plunger-activated switch that screws into the transmission case.
We Have This Part in Stock
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.