EVO: Electrical System


The Reference Section also has related information:

Basic Electrical Concepts

Buying & using a multimeter

See also Current Draw with Key Switch OFF

Wire Gauges - By Circuit

Typically, the MoCo does not publish the wire gauges used on their bikes. However, in the 1995-96 Electrical Troubleshooting Guide (99948-96), the wire gauges used on various circuits were listed. The following list should be fairly accurate for other models of this era, as well. I'm certain that some changes would have occured in later years, but in general, this list should guide you in making repairs of existing circuitry.

Battery cables, required to carry high current loads (up to 200amps) for the starter motor, must use heavy duty wire. Custom made battery cables, being relatively short on motorcycles, are typically made with 4 gauge wire, with 2 gauge wire chosen where the reduced flexibility can be accomodated or where required for a longer run from a more distant battery location.

A general discussion of Wire Gauge & Amperage Rating is included in the Reference section titled Electrical Concepts.

Wire Gauges used in the 1996 XL Main Harness:

18ga wire was utilized for these connections:

  • One of three Main Chassis Grounds
  • Output of 10a/15a CBs (Circuit Breakers) to power circuits
  • Starter Relay Coil Control from Starter Button
  • Coil connections
  • Horn connections
  • Neutral Switch
  • Oil Pressure Switch
  • Ignition Module (except Ground)
  • VOES
  • Cam Position Sensor
  • Lt Switch wiring (except Low Beam)
  • Rt Switch wiring (all)
  • Instrument Cluster
  • Turn Signal Module (except Power In)
  • Rear Turn Signals
  • Rear Taillight
  • Front & Rear Stoplight Switch

16ga wire was utilized for these connections:

  • One of three Main Chassis Grounds
  • Lt Switch for Low Beam to Headlight (only)
  • Ignition Module Ground
  • Turn Signal Module Power In

14ga wire was utilized for these connections:

  • One of three Main Chassis Grounds
  • Into 10a/15a CB - feeds all
  • From Keyswitch to Starter Relay
  • Output of Starter Relay to Starter Solenoid

12ga wire was utilized for these connections:

  • Battery Power to Main 50a CB (from starter stud junction)
  • Main 50a CB to Keyswitch

In a thread by morvenhouse on the XLForum, he included this picture of the difference between his 6-AWG stock battery cable and the 3-AWG battery cable he made: 1)

Wiring Colors - By Function

HD has been quite consistent over the years in selecting wire colors based on the function they perform, although this practice was NOT ABSOLUTE in all models or years.

For example:2)

Blue wire was used for regular lighting power
Yellow wire was used for low beam headlight power
White wire was used for high beam headlight power
Brown wire was used for the right turn signal power
Violet wire was used for the left turn signal power
Orange or Orange/White was used for Accessory power

Connector Options

Here is a link to a great listing of connector and connection options. That web page discusses switches, wiring, connectors and tools. Contributed by Oldrump1 from the XLForum.net 3)

Deutsch Connectors

Example connectors - 6-pin & 12-pin Plug Connectors for Female Socket Contacts


Here's an XLForum Thread that show how to disassemble various connectors.

For Multi-Lock Connectors, here's an animation of Removing the Wire From the Connector:

Battery Cables - The Place to Start

A huge number of issues are caused by battery cable deterioration and/or loose connectors. The negative cable to the frame is especially critical. All Sportster models occasionally have trouble with the battery cables but it seems to be even more prevalent on the rubber-mounted engine models from 2004-up (since the motor moves more in relation to the frame).

(If you're having a No Start issue, after doing everyting mentioned in this section, have a look at the REF section on Troubleshooting a No Start Problem.)

The large Positive Battery Cable goes direct to the Starter Solenoid. There is another wire from the Battery (or from the Starter Solenoid) that feeds the Main Circuit Breaker (or Maxi-Fuse) for the system electrical & electronic devices.

The large Negative Battery Cable on the early models went to rear motor mount. Later, it was moved to the backside of the Primary cavity on the crankcase near the Starter Motor.

“I was checking the voltage at the battery against the voltage at the starter, at first it was the same. I moved the bike to get to the other side and double checked the voltage and it dropped significantly. I nudge the battery once and watched the voltage go to zero! I removed the positive lead and it appeared fine on the outside. One good pull on both ends and the end to the starter and about 2” of copper strands slid out from the insulating jacketing“, said TimC of the XLForum.5)

To check the battery cables - PULL HARD on both ends of both the positive and the negative cables where they mount to the battery and to the engine. There should be no looseness to the cable at the connector junction. Corrosion in the connectors and the wire itself can be hidden from your casual examination yet will still cause severe loss in current capability. Therefore, PULL HARD to be sure they are solid.

If both ends are secure in their connectors, then verify that the bolts at each end of each cable are without corrosion and are firmly tight. Wrench tight.

Then use your voltmeter (multimeter,​ dvm, etc.) to measure the incoming voltage (from the battery) at the key switch. Then measure the outgoing voltage from each of the keyswitch positions. If you still have no power, continue checking downstream, thru the fuses, until you find the break in the voltage circuit.

6) 7)

As you can see in the pictures above, if the connections are not tight even the posts can melt due to high current arcing. In addition to tightening the bolts, you can physically restrain the connectors with a zip tie around the battery post. With proper placement, even the rubber boots can be put back in place.

Battery Charge Level

Battery condition can be seen as the voltage of the battery after it has been charged. To verify that it is in a 100 percent fully charged condition, charge the battery and disconnect the charger. Let the battery rest for one to two hours, then check the voltage level.

AGM Batteries 8)

Voltage Reading 12.7 12.6 12.3 12.0 11.8
Percent Charged 100% 75% 50% 25% 0%

Older-style Sealed Lead Acid Batteries 9)

Voltage Reading 13.0 12.8 12.5 12.2 12.0
Percent Charged 100% 75% 50% 25% 0%

Be sure your multimeter BLACK Probe is properly grounded to the Battery Negative Post or to the frame.

Battery Voltage Readings

From the XLForum.net 10)

Whenever there is a problem that may even remotely be electrical, it is important to know the quality of power with which you are operating. This is why you should have a volt-ohm meter (DVM/Multimeter) and take voltage readings, as described below, as part of your initial diagnostics.

Be sure to connect your BLACK Probe directly at the Battery Negative Post to take a reference Battery Voltage Reading - or use the frame once you have established that the battery voltage (taken on the Battery Positive Post) is the same with the BLACK Probe on the Battery Negative Post -and/or- on the frame.

When there is “no power” at all, check the main circuit breaker or maxi fuse (usually 30amp) located near the battery - Power is supplied from the battery, thru the MaxiFuse to the key switch. Check to be sure the MaxiFuse is not blown - If that is good, then, check all the remaining fuses. The 1997-earlier models (including ironheads) have thermal circuit breakers which are self-resetting. Although quite resilient, these will fail from time to time.

Corrosion can be a real power killer. It can degrade the quality of your voltage significantly and your geographic location can be a factor in the potential for corrosion. Be sure to check both the front and back of the fuse box/panel for corrosion, especially on the 2007-later models where the fuse box is in a very exposed area and subject to standing water.

If the fuses/circuit breakers are OK, check the keyswitch itself.

Remember - Many suspected fuel issues turn out to be electrical. Some suspected ignition module issues (rigid mount) turn out to be voltage quality related. So do a through check on these systems.

Taking Voltage Readings - You need to know the following voltage readings (and provide them to your tech or when asking questions on the forum):

SUMMARIZED - Basic Battery Voltage Test
Take a voltage reading across the battery POSITIVE and NEGATIVE terminals…

1) With the keyswitch off (should be 12.8v or more)
2) With the keyswitch on - but engine not running (should be 12.5v or more)
3) With the keyswitch on, while cranking the starter (should be 10.5v or more)
4) With the engine running with a slightly elevated rpm above idle (should be 13.5v or more)

Also check the Key Switch ←– Link to function & testing info.


  • 1. KEY OFF battery voltage, at the battery: Normal is 12.8, acceptable is 12.6 to 12.8 for no load. If just taken off a charger, voltage may be 13 point something, but battery should be allowed to 'rest' for 1-hour before taking qualified readings. In the case of a bad cell, the other cells overcharge and give an almost normal reading, until load is applied.
    • If lower, then battery is discharged and needs charging or
    • Battery has a bad cell
  • 2. KEY ON battery voltage (headlight on): Normal is not under about 12.5 initially, but will decline the longer that the headlight is on, without the motor running. Under no load, 12.5 volts indicates 50% discharge, but under load, it is just voltage drop.
    • If lower, then battery is discharged and needs charging or
    • Battery has a bad cell or
    • Battery cable(s) have high resistance
  • 3. KEY ON - While Cranking the starter motor: Normal is not under 10.5 volts
    • If lower, then battery is discharged and needs charging or
    • Battery has a bad cell or
    • Battery cable(s) have high resistance or
    • Starter is drawing too much current
  • 4. KEY ON - Bike Running at 2500 RPMs: Normal battery voltage should be 13.8 to 14.8
    • If not, then check stator internal resistance and whether either end of stator is grounded
    • If the stator resistance is within spec and is not shorted to ground, the regulator or regulator ground is suspect

(Above references are to lead-acid battery readings - Readings for AGM batteries are typically .2v lower)

Grounding is Critical

Ground connections on the bike are like a spider web - they should all be interconnected through the various ground bolts, harness connectors and individual components. There should only be a very slight difference in resistance between any two ground points in the entire system. If there is excess resistance between any ground point and the negative battery terminal, there is something loose, frayed, corroded or disconnected.

Over the years, HD has grounded the Sportster electrical systems in a number of ways.

In the early models (typically, 1993-earlier), components were grounded to the frame at a nearby point while power was distributed throughout the system on a minimal number of wires in the wiring harness. There could be as many as a dozen points on the frame used for grounding. The front lights & instruments were grounded thru a connecting strap between the fork risers & the handlebars.


Beginning in 1994, the wiring harness itself began to carry ground wires to various components. The wiring harness by then consisted of many separate power wires to multiple locations, with a number of circuit breakers protecting the various circuits from overload.

The battery ground cable and the common wiring harness ground wires connect to the engine. Up through 2003, the ground wires connected onto the upper left (or right) rear engine mounting bolt. After the bolt & nut secured the engine to the frame, the battery & harness cables are placed onto the extended bolt and a lock nut is then used on the same bolt - this secures the cables to the engine & frame. There were still devices that grounded thru the frame (back to the battery), such as the horn, the oil pressure indicator switch and the neutral indicator switch.


Beginning in 2004, the Rubbermount models have the wiring harness grounds collected to a single point on the engine called the Powertrain Ground Point. Located near the starter motor, this PGP is a dual-threaded stud mounted horizontally to the engine case with the ground wires from the wiring harness attached by a nut.

Similarly, there is another dual-threaded stud to mount the negative battery cable to the crankcase. This ground point is particularly subject to thread corrosion between the stud and the engine because the stud socket on the engine is a vertical hole. When water gets in the threads, causing corrosion, there are erratic electrical problems created throughout the system.

If a bike of these model years experiences erratic electrical problems, be sure to remove this stud and thoroughly clean the female threads on the engine. Then, clean the stud threads on both ends and apply a copper-based antiseize compound on reassembly to provide the best electical conductivity and minimize future corrosion.

Another point that must not be overlooked is the grounding strap that attaches between the engine and the frame. It is located in parallel with the torsion tie bar UNDER THE REAR OF THE ENGINE. Remove the strap and thoroughly clean both connecting points and reassemble with copper-based antiseize compound as suggested above.

A recurring problem has been the battery ground cable from the negative battery terminal to the engine/frame ground point. This cable often fails with internally broken wire strands or excessive corrosion. This condition is aggravated by storing the bike outdoors.

More reading HERE.

2004-later has two main ground points - Engine Case Battery Ground & Power Train Ground (AKA GND1)
(2004-2007 may have these reversed with battery ground on primary cover & harness ground on case stud)

Plus, there is the Engine-to-Frame Grounding Strap under the rear of the engine

Testing for Proper Grounds

It's possible to use a volt/ohm meter, or Digital Volt Meter (DVM), to check the resistance from any ground point on the bike back to the negative battery terminal. Such resistance checks can discover problems. To do this type of check, the meter is set on a low resistance scale (less than 100ohms if possible). The negative battery cable should be removed from the battery (to disable power on the bike). One lead of the meter is placed on the battery end of the battery cable (now disconnected from the battery) while the other end is placed on the ground point being checked. If properly connected, the meter should read a very low resistenace, nearly ZERO (usually less than one ohm).

A quick and dirty test (although not able to detect borderline issues) can be performed with a powered test light connected between the negative battery cable and the ground point under examination. These test lights sometimes look like pens or screwdrivers with a pointed probe and a small internal battery. If the light illuminates, there is a circuit connection between the two points being tested. This is similar to using the multimeter continuity check. The meter also sends power through the circuit to see if the circuit is completed.

There is another method for testing grounds. You can test ground connections using voltage checks. This uses the voltage setting of the meter and does not require you to remove the negative battery cable. With this method, you will use the battery itself to test for continuity to various ground points on the bike. A digitial multimeter (DVM) is prefered for this method.

First, set your meter to read DC voltage where 12 volts is easily measured (maybe the 20v scale). Place the red lead from the meter on the positive battery terminal. In fact, you should find a way to clamp it on that terminal (maybe using a plastic spring clamp). Be very careful not to short the positive terminal to any part of the bike.

Now measure a REFERENCE VOLTAGE. Place the black lead on the negative battery terminal to take an initial voltage reading of the battery itself. This voltage should be close to 12.8 DC volts. Whatever your voltage reading, directly on the battery, will be called the REFERENCE VOLTAGE.

When checking the voltage between the positive terminal of the battery and ANY GROUND POINT on the bike, you should have a voltage reading very close to the Reference Voltage (like 12.8v above). Every single ground point on the entire bike should measure within .3v of this reading.

So, if you take the black lead to the other end of the negative battery cable, on the powertrain ground or engine, it should measure near the Reference Voltage. If you take the black lead to the ground pin on the headlight connector, it should measure near the Reference Voltage. If you take the black lead to the ground pin in the taillight connector, it should measure near the Reference Voltage. If you take the black lead to the cylinder heads (next to the spark plugs), the meter should read near the Reference Voltage.

IN EVERY CASE, the red lead is still on the positive battery terminal and the ground point you are testing should have a good connection back to the negative battery terminal through the ground connections of the wiring harness, the powertrain ground, the frame and the battery engine case ground point. If ANY GROUND POINT does not measure within .3v of the Reference Voltage, there is something loose, frayed, corroded or disconnected which causes the voltage loss. 15)

http://xlforum.net/forums/showthread.php?t=1506137 - Pic from morvenhouse - Annotated by IXL2Relax
sportsterdoc of the XLFORUM.net
Illustration created by IXL2Relax at the XLForum
http://xlforum.net/forums/showthread.php?t=2071578 - Pic from The Doctor71 - Annotated by IXL2Relax
Pic from SportsterPaul
2016 Sportster Owner's Manual
1998 Sportster Service Manual
http://xlforum.net/forums/showthread.php?t=2073777 - Pics from John Harper - Annotated by IXL2Relax
http://xlforum.net/forums/showthread.php?t=1944256 - Pic from decman - Annotated by IXL2Relax
13) , 14)
http://xlforum.net/forums/showthread.php?t=1891463 - Pic from Chopsticks - Annotated by IXL2Relax
Contributed by IXL2Relax of the XLFORUM.net
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