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:
- Faulty light connector
- Battery not connected
- Faulty regulator/rectifier
- Bad light switch/connection
- Corroded/loose connections
- Faulty relay
- Wiring short
- Bad light circuit ground
By the end of this post, you’ll know the likely causes of ATV light flicker, how to diagnose them, and also how to fix them.
The most common cause of light flicker is a loose master connector, and by a master, I mean the connector that carries power to both lights. If both your headlights are flickering, you know, it’s not likely it’s a couple of 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 ATVs, 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 diagnosis with the low-hanging berries first. Hey, we might get lucky. Getting the answer to a few simple questions helps speed up the process.
Questions like – Do your lights flicker on heads and dips or both?
Flickering on both may indicate a failing rectifier or stator, but we’ll get to that later.
Flickering on just dips or just heads may mean a block connector in the main loom is loose, dirty or corroded.
If your bike has twin lights and just one is flickering, then you are likely dealing with a loose light fitting.
Let’s start by eliminating a source of lots of electrical problems.
- Loose connectors at the light fitting, loom or chassis ground
- Battery connections are tight & clean
- Battery is healthy
Light fittings, block connectors and chassis grounds
The lowest hanging fruit of all is the light fitting, the light block connectors, and don’t forget chassis grounds.
Check them first, try the wiggle test – wiggle the light fitting, light loom and block connectors, and the chassis connecting wires with the lights on and see if it helps. While not very technical it’s often the most efficient way to find intermittent electrical problems. We’ll look at this in a little more detail later.
A single flickering could be caused by a faulty bulb itself, don’t rule it out completely.
Battery supply issue
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 voltmeter for these tests. Using a DVOM, go ahead and connect the meter and set it to 20v DC – Red test cable to the positive (+) pole of the battery and the black test cable to the negative pole (-) of the battery.
Most ATVs 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.
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.
Crank test – We run a load test because your battery could show a full 12.65 volts on a volt test, but 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 baking 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, which helps prevent corrosion in the future.
Be sure to tighten the terminals securely. Loose terminals will cause problems.
Your ATV charging system is pretty simple. It consists of a battery, stator, regulator, and rectifier. The battery we’ve already covered, and you know what it does.
The stator lives inside the engine side cover, and its job is to produce voltage. It’s a 3 phase unit, meaning it has three separate windings 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 regulator’s 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 the 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 and up 15.5 when revving the engine.
However, if your voltage rises above 15.5 or it doesn’t change, something’s up in the system, and we’ll need to test.
Checking The Stator
Typically we run a couple of tests to test a stator. A dynamic test with engine running and resistance test with the bike off and stator block connector disconnected.
First, we run the dynamic test. Check the output of the stator by checking the voltage the rectifier receives.
Back probe the stator wiring harness. You’ll see it run from the engine casing to the rectifier, yours maybe a little further back towards the rear of the bike.
A typical stator has three wires, one for each of the windings. Using a DVOM set to AC volts, probe each circuit in turn as per the picture below. Note the voltage.
A typical reading is anything above 15 volts AC. Less than this, or one reading a lot lower than the others suggests a fault, and you’ll need to confirm with a resistance test.
We’ll cover the resistance test next.
Spec varies from model to model, so verify your bike’s spec.
A resistance test is easy, but we’ll need to disconnect the stator block connector altogether, back probing won’t work.
Set meter to resistance, finding a reading outside spec means your stator is at fault.
But spec varies from model to model, so verify your bike’s spec.
Checking these guys using a DVOM can be tricky as model spec varies. Instead, check the battery, cables, and stator output. If all is OK and still not charging, or overcharging by a process of elimination you’ve diagnosed a faulty regulator rectifier. Go ahead and replace the regulator rectifier.
Check 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 contact cleaner 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, 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 holders.
Check your light circuit relays. As they get older, the internal moving components get tired and fail. You may need to swap 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 you’re still chasing your problem, you’ll need to get a little more technical and run a volt drop test. This is a test I regularly perform 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 what’s 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.
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 the ground (Ground is chassis and engine metal components connected to the negative battery pole). By harnessing 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 the 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 Come in Four Flavors
- Open circuit – not connected, caused by broken wire, disconnected connector etc.
- High resistance – connected, but not fully connected, there’s a blockage eg rusty connectors.
- Shorting to ground – the positive charge has found a quicker path to ground, eg chafing positive wire on engine or chassis.
- Shorting to power – less common, chafing of two separate power circuit wires.
The volt drop test 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 the 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) may be caused by many different types of root causes like rusty connections, loose connections, broken or partially broken internal wiring strands, worn switches, corroded wiring, etc.
And since we can’t visually 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 ideal, but I live in the real world where we have to improvise, and I know ATV riders are excellent at that. So, we’ll start testing where ever we can gain access easily and we’ll avoid removing covers, etc. until all the easy-to-access areas are checked.
Power side volt drop test – Test with the lights switched on. A reading above point three volts indicates high resistance.
Check readings back towards the battery to identify the problem area.
Ground side volt drop test – Test with lights on. A reading above point two volts indicates high resistance in the ground side of the circuit.
Check the grounds are clean, tight, and in good order.
A good voltmeter, back probes, and crocodile clips, a test light is always useful, Wire strippers, heat shrink, soldering gun and solder, insulation tape, an 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.
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