ATV Lights Flicker (Solved)

Night riding is challenging enough without the added excitement of flashing and flickering headlights, besides it can be off-putting to other riders and disorientating to you.

The top 8 most common causes of ATV light flicker, include:

  1. Faulty light connector
  2. Battery not connected
  3. Faulty regulator/rectifier
  4. Bad light switch/connection
  5. Corroded/loose connections
  6. Faulty relay
  7. Wiring short
  8. Bad light circuit ground

By the end of this post you’ll know the likely causes of ATV light flicker, how to diagnoses them and also how to fix them.

Loose/Corroded Battery Connectors

The most common cause of light flicker is a loose master connector, and by master I mean the connector that carries power to both lights. If both your head lights are flickering, you know, it’s not likely it’s a couple bulb holders giving the same problem at the same time, right. The problem must be further upstream.

ATV wiring has to deal with a lot, some customers treat them like submarines, they’re caked in mud and years of rough trail riding causes loose connections, chafing, broken wires, wiring corrosion and fretting (micro corrosion) on the wiring terminals.

It’s not a problem to young fit ATV’s, but after a few years, the wiring is one of the first components to let you know it’s not the bike it once was.

I’ll usually start my diagnoses with the low hanging berries first, hey, we might get lucky. Check and see if your lights flicker on heads and dips or both. Both might indicate a failing rectifier or stator, but we’ll get to that later. I start by eliminating a source of lots of electrical problems, I’ll check:

  • Battery fitted
  • Battery connections are tight & clean
  • Battery is healthy

A problem here could cause your lights to flicker, but the symptoms may not be identical for each. If your bike is missing a battery or the battery is faulty, this can cause the lights to flicker, but usually at higher rpm.

A bad battery connection and by bad I mean damaged, corroded or loose, will cause problems and will need to be fixed before proceeding to troubleshoot your flickering lights.

Testing ATV Battery

Testing the battery is a two part process, first we’ll check the voltage and then we’ll load test the battery. We’ll need a volt meter for these tests.

Using a DVOM, go ahead and connect the meter and set to 20v DC – Red test cable to positive (+) pole of battery and the black test cable to the negative pole (-) of the battery.

Most ATV’s are 12 volt systems, some older bikes may run 6 volt systems, either way the voltage will be marked on the battery casing.

Hold the test leads firmly on the battery and record the reading.

  • 12.65 volts 100% charged
  • 12.4 volts 75% charged
  • 12.2 volts 50% charged
  • 12.0 volts 25% charged
  • 11.9 volts discharged (Flat)

A reading below 12.4 volts and your ATV may struggle to crank the engine.

If your battery is low, you can attempt to jump start from another vehicle or charge your battery with a battery charger.

Load test – We run a load test because your battery could show a full 12.65 volts on a volt test, be actually be faulty. To run this test the battery will need to be at least 75% charged. If the battery is soft, you’ll need to charge it first.

For this test we’ll connect a DVOM to the ATV and have a helper attempt to crank it over. If the battery voltage on the DVOM reads below 9.6 volts while cranking for 3-4 seconds, your battery is faulty.

Cleaning Battery Connections

To clean the terminals, use some basking soda and water, but you’ll need to wear glasses and gloves, acid is nasty stuff.

Remove the battery terminals and clean with sandpaper, apply a coat of petroleum jelly after refitting, helps prevent corrosion in the future.

Be sure to tighten the leads securely, loose terminals will cause problems.

Charging System

Your ATV charging system is pretty simple, it consists of battery, stator, regulator and rectifier. The battery we’ve already covered and you know what it does.

The Stator lives inside the engine cover and its job is to produce voltage. It’s a 3 phase unit, meaning it has 3 separate wingdings that each produce alternating current (AC).

The rectifier’s job is to convert ac voltage to direct current (DC), as your ATV’s electrical systems can only use direct current.

The regulators job is to sense battery load and adjust charge voltage output so that it meets the electrical demands of the bike. Note: regulator/rectifiers are combined into one solid state unit.

Checking Charging system

With a DVOM, check battery voltage with the engine at idle, anything above resting battery voltage (12.65) indicates your stator and regulator/rectifier are doing their job. About 14 volts at idle with lights turned on.

However, if your voltage doesn’t change, something’s up in the system and we’ll need to test.

Checking The Stator

Check the output of the stator by checking the voltage the rectifier receives. Unplug the stater wiring harness, you’ll see it run from the engine casing to the rectifier, or back-probe them in place.

The stator has 3 wires, one for each of the winding’s. Using a DVOM set to AC volts, probe any 2 and note the voltage. Now probe the remaining wire and note the voltage.

A typical reading for both is anything above 15 volts AC. Much less than this or one reading a lot lower than the other suggests a fault and you’ll need to confirm with a resistance test, and if so replace the stator.

Check Regulator/Rectifier

Checking these guys using a DVOM can be tricky as model spec varies. Instead, check battery, cables and stator out put, if all is OK and still not charging, go ahead and replace the regulator/rectifier.

Check Main Fuse & Grounds

Checking the light fuse makes sense, these guys are easy to find, check and clean. Corrosion builds on the fuse contact points and fuse holders become loose allowing the fuse to lose contact.

The grounds are usually pretty easy to find on an ATV. Trace the other end of your negative battery cable and check it’s tight. Now check the engine chassis ground, are they tight and in good condition?

Check Light Circuit Connections

With the battery and charging system eliminated from the possible fault list, go ahead and check the light circuit connectors, one by one. Some bikes will be easier than others. Follow the loom as best you can, no need to remove any covers just yet, we’re still just troubleshooting on the fly.

When you find a connector, turn on your lights to replicate the flicker. Using both hands wiggle the connector and see if it makes any difference. Open the connector and check for corrosion, apply dielectric grease to the connector and refit. Repeat this for as many of the connectors as you can find. Don’t forget the loom to the light switch.

Check Light Switch

Remove the light switch and clean the contacts or try spraying some down the side of the light switch, and check light flicker. Light switch contacts corrode and become worn, replacing switches is a common repair.

Only One Headlight Works

If you have only one headlight flickering, then your problem is likely to be bulb fault, holder or a problem at the connector, where the light loom splits from the main loom. Start by swapping the bulb for the opposite side, to eliminate bulb failure before getting to work with sandpaper and dielectric grease on connectors and bulb holder.

Light Relays

Check your light circuit relays, as they get older the internal moving components get tired and fail. You may need to sway out the relay to eliminate it. You’ll often have more than one identical relay on a bike, so swap them around to test. Just because it clicks doesn’t necessarily mean it’s good.

Volt Drop Test

If your still chasing your problem, you’ll need to get a little more technical and run a volt drop test. This is a test I perform regularly when chasing faults. The test is performed on a live circuit and you’ll need a DVOM and some back probes would be great.

I know most of you already know this stuff, but for those that are foggy, here’s a very basic explanation of whats going on and what we’re looking for. This stuff is simple, so stay with me here because this test will help you nail your problem down.

Electricity as you know moves in a circle (circuit) and the positive charge from the battery is constantly searching for the shortest possible path to a ground (Ground is chassis and engine metal components which are all connected to the negative battery pole). By harnessing the the voltage and forcing it to pass through a light bulb, the bulb lights up.

But if instead some of the positive voltage found a path to ground before it got to the bulb, the bulb would be less bright or flicker. An example of this is a chaffing power wire off the chassis, it’s a common fault.

Wiring Problems Four Flavours

  1. Open circuit – not connected, caused by broken wire, disconnected connector etc.
  2. High resistance – connected, but not fully connected, there’s a blockage eg rusty connectors.
  3. Shorting to ground – the positive charge has found a quicker path to ground, eg chafing positive wire on engine or chassis.
  4. Shorting to power – less common, chafing of two separate power circuit wires.

This test simply identifies high resistance (blockage) between two points in a circuit. It does this by measuring the difference in voltage on one side of a connector, for example to the other. A high reading indicates the connector may be corroded.

This test will only work on a live circuit, so you’ll need your lights turned on and bike running. The test is performed on the positive side and on the ground side of the circuit.

In the case of your ATV’s flickering lights, you have a resistance issue. The resistance (blockage) can be caused by many different type root causes like, rusty connections, loose connections, broken or partially broken internal wiring strands, worn switches, corroded wiring etc.

And since we can’t see into the wiring and stripping the bike to examine the complete circuit would be laborious, we will instead check various sections of the light wiring circuit. A systematic approach would be nice but i live in the real world where we have to improvise and I know ATV riders are excellent at that.

Start where ever you can gain access easily and remove covers etc only when all the easy stuff is checked.


A good volt meter, back probes and crocodile clips, a test light is always useful, Wire strippers, heat shrink, soldering gun and solder, insulation tape, assortment of insulated connectors and a knife.

I avoid piercing the wiring loom if I can and instead back probe the connectors. But when I have to pierce the wiring insulator I’ll wipe some silicone sealer into the wound. It prevents future corrosion.

John Cunningham

John Cunningham is an certified mechanic and writer on I’ve been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance, repair to troubleshooting.

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