Jeep J20 Relay Guide for 1984-1988 Models
Understanding, diagnosing, and replacing essential relays in your classic J-series truck.
- Relay failure often causes a no-start or intermittent electrical issue.
- Diagnosis is simple: swap the suspect relay with a known good one to see if the problem moves.
- Replacement is an easy, plug-and-play job that requires no special tools.
- Aftermarket relays are the standard for this vehicle and are a reliable, cost-effective choice.
Understanding Relay Failure in Your J20
The relays in your Jeep J20 are simple electromagnetic switches that have been in use for decades. While generally reliable, their internal components can wear out or burn out over time from heat and repeated use. A failing relay can cause frustrating and hard-to-diagnose electrical problems. Symptoms often appear suddenly and can be intermittent, making it tricky to pinpoint the cause.
Symptoms of a Bad Relay
A bad relay can cause a wide range of issues depending on which circuit it controls. Here are the most common signs to look for:
- Engine Cranks but Won't Start: This is a classic sign of a failed fuel pump relay. The relay isn't sending power to the fuel pump, so the engine isn't getting any gas.
- No-Crank, No-Start: If you turn the key and nothing happens—no clicking, no cranking—the starter relay could be the culprit. It's failing to send the high current needed to engage the starter motor.
- Component Works Intermittently: If your horn, lights, or fuel pump work one minute and not the next, the relay controlling them may be failing. Jiggling wires or tapping the relay might temporarily make it work again.
- A Clicking Sound Without Action: You might hear the relay click when you turn the key or flip a switch, but the component (like the starter) doesn't activate. This often means the relay's internal switch isn't making a good connection.
- Component Stays On: In rare cases, a relay can fail in the "closed" or "on" position. This could cause the fuel pump to run continuously even with the key off, draining your battery.
A Note on J20 Electrical Systems
Electrical systems on older vehicles like the J20 can be finicky. Previous owners may have modified the wiring. Before replacing a relay, always check for simple issues first: ensure your battery terminals are clean and tight, and inspect the fuses in the fuse block, which is typically located under the dashboard to the left of the steering column.
Choosing the Right Aftermarket Relay
For a vehicle from the 1980s like the J20, original OEM (Original Equipment Manufacturer) relays are generally no longer available. The market consists of aftermarket parts sold under general labels like "Replacement."
Don't be concerned about the lack of a big brand name. These relays are standard, time-tested components. The key is to ensure the new relay matches the specifications of the old one. Check the pin configuration (the number and layout of the metal prongs) and any amperage ratings printed on the old relay. A standard aftermarket replacement will restore function just as well as the original part.
Part Cost Comparison
| Part Type | Price Range | Notes |
|---|---|---|
| New Aftermarket | $17.03 - $17.03 | The most common and readily available option. Meets or exceeds original specs. |
| New OEM | Not Generally Available | Original Mopar parts for this model year are largely discontinued. |
| Used OEM | Varies | Can be found at salvage yards, but reliability is not guaranteed. |
Pro Tip: Buy a Spare
Because relays are inexpensive and a failure can leave you stranded, it's wise to buy a spare. Keep an extra starter or fuel pump relay in your glove box. It could save you a tow bill down the road.
Frequently Asked Questions (FAQ)
Where are the relays located on a 1984-1988 Jeep J20?
While locations can vary, the starter relay on many Full-Size Jeeps of this era is a silver, cylindrical or boxy component mounted on the passenger-side inner fender well. Other relays may be found in the main fuse block under the dash or near the components they control. Always trace the wiring from the non-working part to find its specific relay.
Can I replace a relay myself?
Yes, this is one of the easiest repairs you can do. Most relays are plug-and-play. Simply locate the old relay, unplug it, and plug the new one in. No special tools are required, though sometimes a gentle pull with pliers might be needed if the connection is tight.
Is it the relay or the starter/fuel pump?
A good test is to swap a suspect relay with an identical, known-good relay from another circuit (like the horn). If the problem moves to the other circuit, you know the relay is bad. If the problem persists, the issue is more likely with the component itself or the wiring.
Are there any recalls for Jeep J20 relays?
No, there are no active or past recalls specifically for relays on the 1984-1988 Jeep J20 according to NHTSA records.
Technical Specifications
Match the pin configuration and voltage/amperage ratings of the original relay.
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.
- Jeep J20: