Overcharging Problem? at idle multi-meter reads 15v(ish) but with some choke gets up to 18v

This is sort of a continuation of my last thread where no power was getting to any fuse but main. after unplugging and replugging stuff in (also fixing some bad solder spots from the PO) everything is powered and the bike runs. Tested the battery and was bad so I got a nice new one.

With the new battery installed bike warmed up and running I noticed the BATT warning coming on randomly so I double checked the red lead that hooks directly to the positive cable and it was connected. With a multi-meter at idle the reading goes crazy like the multi meter is freaking out from 0-15 up and down really fast. sometimes the reading is a steady 15ish. with some choke (I mean enrichment) or a bit of throttle the reading jumps up to 18 and freaks out again.

I have read all the electrical overload stuff and 18v is a no no, is the only fix to clean up all connection corrosion?

If you havent read my previous thread bike is an 82 xj750 seca
Multi-meter is a quality craftsman and is a known good one
setting on the multi-meter was 20dcv
Tach does not work so I dont know my rpms
AGM new battery tested at O'reillys charged and good

 

Yes, check, clean, and test all connections especially the ones having to do with the charging circuit. Also I would recommend cleaning the commutator rings with an eraser and checking the brush length. If all that checks out then I would suspect a regulator rectifier issue. Not sure if this will be clear enough to read but this is at least part of the FSM charging system tests. Someone else may have a clearer to read version

 

Thanks ill give that a shot.

 

voltage regulator is likely your problem
If your charging voltages are too high, suspect your Regulator - Rectifier unit first, and perhaps dirty or corroded electrical terminals. The procedure for checking these is too detailed to describe here, and you should consult your service manual for additional details.

read this thread at bottom is charging system info
https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

 

Double check your meter with a good steady supply voltage (regulated benchtop supply, or a brand-new 9v battery) to rule meter faiulte out.
If the charging voltage still reads high then you have a bad voltage regulator, and it will need to be replaced.

The battery monitor lead is not supposed to be directly hooked to the positive battery post, unless it has a resistor fitted to it so that the monitor can see the correct voltage (the original sensor was fitted to a single cell of a wet-cell battery). There is a thread in the DYI section that details the required modification. Just hooking it up directly will keep the warning from triggering, but not give you any useable data about the state of the battery.

 

yeah the monitor has the proper resistor on the lead. really doubt the multimeter is bad but ill test it anyway.

 

yup yup thanks for the link

 

new 9 volt battery is cheaper than a regulator

 

Looks like the voltage regulator is probably the issue. the connector is partly melted on a few wires.
Not sure on the multi meter, with a new 9v battery the reading was close to 12v and with a freshly charged 1.2v AAA it read at 1.4v
I removed the connector and put all wires together with some connectors to see if the multimeter would do the same thing and it did but now I dont trust the multimeter, may get a new one and try again.
haynes manual says I need 2 meters to properly test the regulator, kinda sucks because I think my current one is bad.
Tci box next to the regulator looks ok no burned connectors and they are clean now.

 

there's 3 white cloth covered wires that come from the alternator to a plug that has a habit of melting, check that too.
the R/R might be good and it's that plug that causing the problem
a new 9v battery is about 9.6v, that 18 volts you measured will start popping bulbs