Adding a Fuse Block and Relay to a UTV

Picture a 2021 Can-Am Maverick in a driveway with three accessories jammed into one factory tap: a 20 inch light bar, a Bluetooth soundbar, and a USB charger. Flip on the lights and crank the stereo, and the fuse pops in under a minute. That tap was built for one small accessory outlet, not a light bar and a stereo together.

The fix is not a bigger fuse. Stuffing a 20 amp fuse into a slot rated for 10 amps protects nothing, it just lets more current cook a connector that was never sized for it. The real fix is a dedicated fuse block fed by its own wire from the battery, switched by a relay, and grounded at its own clean point.

Done right, a 6 to 12 circuit block takes about 90 minutes to wire in and gives every future accessory, from heated grips to a winch remote, its own fused, switched slot. Here is how to size it, mount it, and wire it so it works the first time.

Why One Factory Tap Cannot Run Three Accessories

Most factory accessory circuits are fed by a 10 or 15 amp fuse off a switched, key-on source, plenty for the single 12 volt outlet it was designed to feed.

Add a 10 amp light bar, an 8 amp stereo, and a 3 amp charger to that same tap and you are asking one small connector to carry 21 amps. The wire heats up, the crimp loosens from thermal cycling, and voltage at the far end sags under load. That sag is why accessories dim or reset the moment you flip on one more switch.

A voltage drop test tells the story fast. Load up all three accessories and measure across the connector. A healthy connection reads under 0.2 volts. An overloaded tap commonly shows 0.6 to 1.1 volts of drop right at the plug, lost as heat inside the connector.

Choosing a Fuse Block Sized for What You Are Actually Running

Start by listing every accessory you want to run, current and planned, with its rated draw. A 20 inch light bar draws about 10 amps, a 40 inch bar closer to 18, a marine style stereo runs 8 to 10 amps, a USB charger 2 to 3 amps, and heated grips 3 to 5 amps. Add them up before you buy anything.

A 6 circuit blade fuse block, about 18 to 25 dollars, covers a light bar, a stereo, a charger, and two spare slots. A 12 circuit block, 30 to 45 dollars, makes more sense once a winch remote, rock lights, and a compressor are on the list. Buy one size larger than today’s plan to avoid pulling the block back out next season.

Look for mini or standard blade fuse slots, a shared positive bus, and an independent negative bus so every accessory grounds right at the block. A clear cover and gasket keep dust and splash out.

Picking a Mounting Spot That Stays Dry

Mount the block inside the dash, under a seat, or in a sealed console, never in the wheel well or belly pan spray path. Keep it at least 8 inches from exhaust heat, and leave 12 to 18 inches of slack in the main feed wire so it can be pulled for service.

Add a small drip loop in the wire before it enters the block so water runs off instead of tracking into the connector body.

Wiring the Relay So the Block Shuts Off With the Key

A standard 5 pin, 30 to 40 amp automotive relay costs 6 to 10 dollars and is the difference between a fuse block that drains the battery overnight and one that shuts off the instant you pull the key.

Pins 86 and 85 are the coil. Pin 86 goes to a switched, key-on source, checked first with a meter (12 to 12.6 volts key on, 0 volts key off). Pin 85 grounds. Pin 30 is the constant battery feed, protected by the main fuse. Pin 87 is the switched output feeding the block’s input stud.

The coil only pulls 150 to 200 milliamps from that switched circuit, so it will not overload a wire already feeding a gauge cluster or ignition relay. The real current, the 20 to 40 amps the accessories draw, travels through pins 30 and 87 on its own heavy wire.

Sizing the Main Feed Wire and the Main Fuse

Add up the accessory list again and size the wire and fuse for the worst case, not for today’s two accessories.

For the light bar, stereo, and charger example above, the combined draw is about 21 amps with everything running at once. An 8 AWG feed and a 40 amp main fuse leaves headroom for heated grips or a compressor added later. A 12 circuit block feeding a winch remote and rock lights can push past 50 amps, where 6 AWG wire and a 60 amp main fuse earn their keep.

Use an ANL, MIDI, or MEGA fuse holder rated for the wire size, 12 to 18 dollars, mounted flat against the frame near the battery tray, not zip tied loose where it can swing into a moving part.

Grounding the Block So It Actually Works

A hot, switched fuse block with a weak ground behaves like a bad ground anywhere else on the machine: dim lights, a stereo that resets, a charger that drops out over bumps.

Run a ground wire matched to the main feed gauge, an 8 AWG feed gets an 8 AWG ground, from the block’s negative bus to the battery negative post or a cleaned frame ground point. Sand the mounting point to bright metal, use a star washer, and torque a typical M6 ground bolt to about 80 to 100 inch-pounds rather than just snugging it by feel.

Check the work with a voltage drop test. With every accessory switched on, put a meter across the new ground connection. A clean ground reads under 0.2 volts. Anything over 0.5 volts means the paint was not fully cleaned off, or the ground point is a poor choice.

Wiring Accessory Circuits and Testing the Whole Install

With the block mounted, grounded, and hot only with the key on, wire each accessory to its own slot. Match the mini blade fuse to the accessory’s real draw plus about 25 percent. A 10 amp light bar gets a 15 amp circuit, not a 30, so the fuse still protects the wire if that circuit shorts.

Test in this order. Key off, meter on the block’s input stud, should read 0 volts. Key on, same point, should read battery voltage, 12.6 to 14.4 volts with the engine running. Listen for the relay click, and confirm continuity between pins 30 and 87 with a meter while it is energized. Then switch on every accessory at once and recheck voltage drop at the feed and the ground. Combined, it should stay under 0.3 volts.

One block a customer brought in last spring had every symptom of a bad relay: the stereo cut out over washboard trail but worked fine sitting still in the shop. The relay tested fine on the bench. The actual fault was the ground ring terminal, tucked under a plastic dash bracket screw instead of bare frame, which only opened up under vibration. Moving the ground to a cleaned bolt on the frame fixed it in about ten minutes and it never came back.

• Add up the rated amp draw of every accessory the block will feed
• Choose a fuse block with two more open circuits than you need today
• Size the main feed wire and fuse to the combined load
• Fuse the main feed within 7 inches of the battery positive post
• Ground the block with wire matching the feed gauge to bare, cleaned metal
• Test key off and key on voltage at the block before wiring a single accessory

What to Check After the First Real Trail Ride

Plan on a five minute recheck after the first ride that works the suspension and gets everything hot with mud, heat, and vibration. Retorque the ground bolt and fuse holder terminals once, since new crimps settle in the first few hours of use.

Keep a spare of each fuse value in the glove box, the mini blade sizes and the main ANL or MIDI fuse for the feed. A 40 or 60 amp main fuse rarely blows on its own; if it does, something downstream shorted and deserves a look before dropping in another one.

From here, adding the next accessory is simple. Pick an open slot, size the fuse to the load, and run a wire to the block instead of back to the battery. The block, the relay, and the main feed wire are already sized to carry it.

Frequently asked questions

How many amps can a typical UTV fuse block handle?

Most 6 to 12 circuit blade fuse blocks are rated for a 30 to 60 amp main feed, with each individual circuit limited by its own mini blade fuse, usually 5 to 20 amps. Add up your accessory list before buying so the main fuse and feed wire match your real total draw, not just the block maximum rating.

Do I need a relay if I already have a switch for my accessories?

Yes, a small dash mounted switch is only rated for a few amps, nowhere near the 20 to 40 amps a loaded fuse block can pull. The relay carries the heavy current on pins 30 and 87 while the small switch or key on wire only triggers the coil at 150 to 200 milliamps.

Can I ground the fuse block to a random bolt on the frame?

Only if you clean that bolt to bright metal and confirm the ground with a voltage drop test, reading under 0.2 volts with the accessories loaded. A painted or rusty bolt often reads fine with a plain continuity check but shows 0.5 volts or more once current is actually flowing, so test it under load.

What size main fuse should I use for a 6 circuit block?

Add up the rated draw of everything you plan to run. A light bar, stereo, and charger drawing about 21 amps combined is well covered by an 8 AWG feed wire and a 40 amp main fuse. A fully loaded 12 circuit block pulling closer to 50 amps needs 6 AWG wire and a 60 amp main fuse instead.

Why does my fuse block drain the battery overnight?

That almost always means the block is wired straight to a constant battery feed instead of through a relay triggered by a switched, key on source. Test the block input stud with the key off, it should read 0 volts. If it still reads battery voltage, move the trigger wire to a source that actually shuts off with the ignition.