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Charging system diagnoses Plus the "Free Power MOD"

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Much of the basic info in this article has been provided previously by TT Member Noble in various individual posts he has contributed to the DRZ Forum.

This article has been editied for content, organization, visuales and compleation to it's published form.

This preventative Maintenance "fix" is applicable and recommended for all year and model year DRZ 2000 -Present

Diagnosis needs to start with a tested, known good fully charged battery.
What have you done to charge the battery? Starting then running the bike 10 min will not do much.
Have the battery charged (overnight on a charger) then have the battery load tested. When you have a good fully charged battery, check for charge voltage at the battery with the bike running.

The electrical system is composed of 5 main components:
1. AC generator (the stator and magnets in the flywheel)
2. The rectifier
3. The regulator (the rectifier and regulator are combined in 1 box but function independently)
4. The battery
5. And the wires that connect everything.

First things first - check the charge voltage at the battery. Battery needs to be fully charged. Running 3000 rpm you are looking for 14 volts or higher. If voltage is low, start troubleshooting the system

Stator and wires. The stator is easy to check and the source of all power so check that to verify it is good. Check short to ground, coil resistance and running AC voltage of all 3 phases as described.

It is very important to check all wires and system ground wires. You have to be systematic and comprehensive. There are no secrets or short cuts

Check the 2 pin plug from the RR. From the battery, trace the small red wire and the small black wire to the first connector. Check those 2 connections. They must be perfect. Check and replace the fuse. Look closely at the fuse holder. The fuse must be a tight fit. Check the 3 pin connection between the stator coils and the RR. Any heat tint or melting of wires or connector plastic here or anywhere else is a problem. (See free power MOD below for more info)


1) Check all connections in and out of the regulator/rectifier (RR) 3 yellow wires and 1 each black (black has a white trace) and red. Trace the red to the battery and check all connections, the fuse and fuse holder and battery terminals. Now do the same with the black wire. You are looking for any signs of heating, loose or dirty or corroded connections. Fix if you find any. Test connections with your hands to feel for any heat (under load). Hot connections are bad.2) Use a voltmeter set at DC for the battery. There are four tests here; Engine off key off, Key on, lights on, motor off, Engine running at idle, Engine running High idle.These test needs to be done with a good and fully charged battery.

  • Engine off, key off - you should have 12.8 or more volts (DC).
  • Engine off, Key on, lights on - around 12 volts (DC) is good.
  • Engine running at idle - above 13 volts (DC) is good.
  • High idle to around 3000 rpm - 14 to 14.5 volts (DC) is what you want to see. (Note Suzuki Spec is @5000 RPM and 13.5-15v)


Suzuki says 13.5 is OK but that will not keep a battery charged in most cases. Many DRZ's will show the highest voltage at idle and the voltage drops as the rpm goes up. That is ok if it is above 14 volts. It is not really dropping but your test meter thinks so.

3) Low voltage - start by checking the stator coils. Unplug the single plug with 3 yellow wires from the RR. Engine off: On the stator side of the plug, check each yellow to ground. No continuity is good, any continuity is bad. Now check wire to wire: Y1 to Y2, Y2 to Y3, and Y3 to Y1. You should see about .5 ohm resistance. Any open is bad, any continuity is good.
With the stator still unplugged from the RR, start the engine and check the AC voltage output between the yellow wires: Y1 to Y2, Y2 to Y3, Y3 to Y1. You are looking for about 60 volts AC at approx 3000 rpm. Exact output is not critical but should be about the same for all 3 readings and above 50 volts. Voltage varies with RPM. Make sure you use the AC scale. ( The factory Service Manual Spec is More than 75v AC @ 5,000RPM, however even brand new serviceable DRZ charging system will show something above 60 to 80v AC many times) If any of the stator coils are shorted to ground, the stator AC voltage output can still test OK open circuit. But when you plug it into the R/R it will not work because you have a common ground for both the AC input and the DC output. That is why you must do (and pass) all 3 tests.

4) Regulator / Rectifier testing - remove the R/R from the bike. You can test the internal rectifier diodes. Put your digital meter on diode check and follow the meter test instructions. Check red wire to yellows wires then reverse the test leads. You will get no continuity one way and about .5 volt drop fwd continuity the other. Now repeat the test black wire to yellows. You should get the opposite results for no continuity and fwd continuity with a .5 volt drop. If you are not using a digital meter with diode test function, use a 12 volt battery and a low wattage bulb and test for continuity vs no continuity.
There is no good way to test the regulator part of the combined R/R unit, except by elimination of all other problems, or substitution with a known good one. The DRZ is not known for R/R failure. But good diagnostic process demands it be tested and eliminated as an issue, as well as being an older design diode style rectifier VS a more robust and longer living MOSFET design so hard part failure on the OEM DRZ R/R should always be considered a possibility, even if not common.

More info, some redundant

Look at all the wires and connections between the R/R and the battery. Both positive and negative. Look at the fuse and the fuse holder. Try a new fuse (fuses can go bad without going open)

NOTE: For the following test it is important to understand the R/R must be connected to a load (the stator and battery) when conducting this test. The R/R cannot be tested for voltage if it is not under load.

If you don't find anything otherwise faulty at this point, make a test connection so you can test voltage at the regulator red and black wires right at the R/R. You are going to have to improvise so you don't poke holes in the insulation which is always bad to do.



It is recommend to rewire the R/R output (charge wire) direct to the battery. This has come to be known as the "Free Power" mod, due to the increase in voltage measured at the battery after this MOD has been performed. The stator and R/R system are not producing any additional power, you simply have eliminated the common faulty OEM plug, and excess wiring length, part of the OEM system that through resistance lowers the amount of power getting to the battery, hence "Free Power" is measured after this MOD..

You will need 14 gauge high quality automotive wire (marine grade wire is a great choice if you can source it).

Fuse and fuse holder or Circuit breaker 

Ring terminals.

Heat Shrink tube ( adhesive lined preferred)

Cut both the Red and Black wires about 4" from the R/R.

Insulate the cut red and black wire leading back to the wiring harness by; cutting off all exposed copper wire back to insulation and use heat shrink tube to cover the wire ends.

sealing a wire.jpg

NOTE: Another option is to use the positive and ground wires just cut and leading back into the harness, for a battery tender plug... 

Next you will extend the now cut R/R Red and Black wires from the R/R to the battery terminals.

The Red positive wire can have a 20 amp fuse or circuit breaker installed as close to the battery as possible to safe guard the charge wire in the event the wire, stator, RR short out. Its never been seen and reported, its not been done that way in thousands of times this Mod has been done, but its still not a bad idea to install the safeguard.. So by all means install a sealed type ATO fuse holder or marine rated circuit breaker in the positive charge wire, and place it as close to the battery as possible.

Even if all the connections are good, this mod will give about .5 more volts to the battery.

You should be very comprehensive with checking all the wires and terminals and connectors. Suzuki uses small wires and small connectors and any sign of heating will cause problems.


Ground wires are too often overlooked but are just as important as the positive feed wires. Something as simple as the small black wire from the battery to the harness can stop everything. That is the only place the loads (other than the starter) are grounded.

There is 1 more thing to check . That is current leakage. With every thing off, disconnect the battery neg. Connect a light between the battery and the cable. Should get nothing. If the light glows you have a big current leakage problem. If no glow, continue. Use the 10 amp scale and connect between the bat an the cable. If less than 1 amp go to the milliamp scale. For an E bike you are looking for less than 1mA current leakage. For the S and SM with LCD instrument display, current leakage up to 2 mA has been found to be normal.

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