Guide to the 1979-1981 GMC P2500 Back Up Light Switch
Getting your reverse lights working is a critical safety repair—here’s how to choose the right switch for your P2500 van or chassis.
- You must identify if your P2500 has a manual or automatic transmission before ordering, as the parts are completely different.
- Always check the reverse light bulbs and the 'TURN B/U' fuse before replacing the switch.
- A new aftermarket switch from a brand like Standard Ignition is the most practical and reliable repair option for this vehicle.
- Driving without functional reverse lights is a safety hazard and may be illegal.
Is Your Back Up Light Switch Failing?
A bad back up light switch on these classic GMC workhorses has very clear symptoms. However, before you assume the switch is the problem, always check the simple things first.
Pro Tip: Before buying a new switch, check that the reverse light bulbs aren't burned out. Then, check the fuse panel for a blown fuse, often labeled "TURN B/U". A bad bulb or fuse is a much easier fix.
Symptoms of a Bad Back Up Light Switch
- No Reverse Lights: The most common symptom is that the reverse lights do not come on at all when you shift into reverse.
- Lights Won't Turn Off: The switch can fail in the 'on' position, causing your reverse lights to stay on constantly, even when driving forward.
- Flickering or Intermittent Lights: You might notice the lights flicker or that you have to jiggle the gear shifter to get them to work. This points to a worn or misadjusted switch.
- Blown Fuses: If the switch shorts out internally, it can repeatedly blow the fuse that controls the backup lights and sometimes the turn signals.
Choosing the Right Aftermarket Switch
For a vehicle from this era, finding a new original equipment (OEM) part from GM is highly unlikely. The market for the 1979-1981 P2500 is served almost exclusively by new aftermarket parts. Brands like Standard Ignition (a brand of Standard Motor Products) are a common and reliable choice, manufacturing direct-fit replacement parts that meet or exceed original specifications.
Critical Ordering Information: The single most common mistake is ordering the wrong part. You must know if your P2500 has an automatic or a manual transmission. The switches are not interchangeable.
- For Automatic Transmissions: You will need the combination Neutral Safety / Back Up Light Switch that mounts to the steering column inside the cab.
- For Manual Transmissions: You will need the screw-in switch that mounts directly on the side of the transmission case.
Aftermarket Back Up Light Switch Cost for 1979-1981 GMC P2500
| Part Type | Price Range |
|---|---|
| New Aftermarket (Standard Ignition) | $26.16 - $53.37 |
| New OEM | Unavailable |
| Used OEM | Varies, but not recommended due to age |
Prices are estimates and may vary based on the specific switch for your transmission and the retailer.
Frequently Asked Questions (FAQ)
Where is the back up light switch located on my P2500?
It depends on your transmission. For an automatic, look inside the cab, under the dashboard, at the base of the steering column near the firewall. For a manual transmission, you will need to look under the truck on the driver's side of the transmission case.
Can I replace the back up light switch myself?
Yes, this is a DIY-friendly job for most home mechanics. For automatic models, it requires working in the tight space under the dash. For manual transmission models, accessing the switch can be difficult without a lift, and sometimes requires a special or modified 7/8" socket to remove due to limited clearance. Always disconnect the battery before starting any electrical work.
My reverse lights still don't work after replacing the switch. What now?
First, re-check the bulbs and fuse. If you have an automatic, the new switch may need to be adjusted on the steering column to engage correctly. If that doesn't work, the problem is likely in the wiring. Check for a bad ground wire at the tail lights or use a test light to check for damaged wiring between the switch and the lights.
Are there any recalls for the P2500 back up light switch?
No. Searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls specifically for the back up light switch on the 1979-1981 GMC P2500.
Technical Specifications
Location and type are dependent on transmission. Automatic transmission switches are mounted to the steering column. Manual transmission switches are screwed 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.