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Your vehicle has a variety of electrical components that power everything from the air conditioner to the taillights. When something goes wrong, it can be hard to diagnose the problem with one of those components, but when it comes to a vehicle’s electronics, there’s a decent chance the problem is related to a relay. 

Several electrical components in your vehicle are controlled by relays. They function like switches, letting one circuit control another, despite differences in amperage. When they go bad, it’s important to know where the problem lies, so that it can be safely fixed without damaging the vehicle. Thankfully, testing a relay is a task that even amateur mechanics can handle. 

The Drive’s crack informational team is here to help, so let’s dig in!

Estimated Time Needed: 30 minutes to an hour, depending on skill level and the relay location

Relays can be found in nearly any vehicle, and are even used in marine and aviation applications. They’re generally used to allow a low amperage circuit to control a higher amperage circuit. Relays act as a switch, allowing the low amperage circuit to turn the high amperage circuit on or off. 

As an example, imagine your vehicle’s headlights. If you connected the lights directly to the on/off switch in the vehicle’s dash, the amperage could exceed the switch’s capacity, which can cause melting wires and even a fire in some cases. Relays can also control multiple systems at once, such as activating headlights when windshield wipers are turned on, or extending an antenna when the radio is turned on.

Relay testing is a simple process, but don’t skip out on safety.  It’s a good idea to take these things into account when working with relays:

Checking your vehicle’s relays is a simple process that doesn’t require an entire toolbox to complete. To check for faulty relays, you’ll need:

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

If you’re short on garage space and plan to work on your vehicle in the street, check your local laws to make sure you’re not violating any codes. Every state and town has different regulations on this type of thing, and we’re not going to help bail out your car if the situation goes south.

Here's our step by step process in picture form.

You’ve done it! Way to go!

The Drive recognizes that while our How-To guides are detailed and easily followed, a rusty bolt, an engine component not in the correct position, or oil leaking everywhere can derail a project. That’s why we’ve partnered with JustAnswer, which connects you to certified mechanics around the globe, to get you through even the toughest jobs. 

So if you have a question or are stuck, click here and talk to a mechanic near you. 

Here at The Drive, we’ve tested our fair share of relays over the years and have found that the simplest method is best. That said, here are a few helpful tips from us pros.

You’ve got questions, The Drive’s info team has answers!

Ignoring a misbehaving relay or slapping in any old relay that fits can lead to big problems under your hood. If a relay is malfunctioning or if an incorrect relay is installed, you can end up frying wires and potentially starting a fire under your hood. Not a good look at 80 mph on the highway.

No. If you’re convinced that there’s a problem with a relay and don’t have the tools to test, you have two choices. You can be cautious and just replace the relay, which is the easiest path forward, or you can pay a mechanic to do the testing and changing of relays for you. 

Most relays should be located in locations that can be accessed quite easily, but if there’s one that you’re unsure about, it’s best to have a professional check it out. Digging around blindly under your hood can damage good relays and do a number on your knuckles in the process.

Pump the brakes. We’re recommending that you fall back on a vehicle-specific repair manual for help locating the correct relay, replacing it with the correct relay, and to make sure that you understand what you’re looking at. Every make and model is different, and even the same model can differ greatly from year to year, so it’s best to have a guide for your specific vehicle to fill in the gaps that the super-brains at The Drive may have missed.

Given the number of electronic devices and systems in modern vehicles, it’s safe to say that nearly all new vehicles have relays.

The most expensive part of testing and replacing relays in your vehicle is the relay itself. Depending on what it’s controlling a relay can cost anywhere from $5 to several hundred dollars.

Ohmmeters can be purchased for less than $20 and come in a variety of designs. High-impedance test lights are slightly more expensive, usually costing between $20 and $40, but spending more doesn’t necessarily net a better product.

Finally, jumper wires are cheap, ranging in price from $2 to over $50, depending on the length of the wire.

Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com

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