Classic F650 Battery Overcharging Fix

Summary: This fix is fairly easy. Obtaining the various electrical bits is probably the hardest part. I realized about a .55 volt reduction in voltage charging the battery at 4,000 RPM with only the low beams on. Increasing the load on the system had little effect until overload occurred. A very stable voltage of between 14.30 and 14.38 volts was obtained after the fixed, again at 4,000 RPM. I was able to scavenge almost all electrical parts other than the diode and various connectors from an old BMW auto I have hanging around. This document assumes you have printed the latest VR wiring diagram and have it handy.

Bill of Materials

1 1 12V 30A relay 2 6 Female Spade Connectors – insulated or covered 3 1 Long Male Spade Connector with retention tab similar to the stock male connector on the green wire from the VR to the harness. (you can bypass this method if desired by not using the original connector for the green wire.) 4 1 3A diode – loose 5 2 ¼ inch stud connectors. They look like lollipops with holes in them, similar to the ground connectors on the frame nearest the fuses. 6 3 feet of #12 wire though #14 would probably be fine. I am always accused of overkill. I would just get some green, red and brown. 7 ? feet of electrical tape and/or shrink tubing, whatever you like.

What I Did or Will Do

1 I did not cut the green wire. In fact, I cut no stock wiring. I did each wire all the way before moving to the next. I laid the relay in between the VR and the back of the bike in the back part of the under- seat tray and tried to keep the wiring the same length so that when I was finished I could wrap the end of it up, including the relay and push the wires in an “S” fashion so that I could eventually just lay the relay down where it would be out of the way. 2 So, starting with the VR side of the green wire, disconnect the plastic connector that connects the green wire and the red/white wire to the rest of the harness. Reach down into the plastic housing with a small screwdriver and depress the metal tab on the long male connector and remove it from the housing. 3 Get about a four inch length of green wire with a female spade connector on each end and used it to connect the long male end of the green wire with terminal #30 of the relay. Tape or shrink-tube the male/female connection between new and stock wires. 4 Make a long male connector with two green wires coming out of and connect it to the now vacant half of the connector I mentioned in number two. You can use a regular male connector and just crimp two wires into it and bypass the stock connector, but you will have to take out the female connector. From this two wire connection to what was once the VR side of the plastic connector, take one wire and connect it to terminal #86 of the relay using a female spade. Solder the second wire to the end of the diode with the band at the top of the barrel facing the two-wire connection, not the ground. To the other end of the diode solder a wire that will become the ground (you can use one piece of shrink tubing to cover the whole mess). I would use brown wire for this. 5 Take another piece of brown wire 6-8 inches long and along with the ground you created in #4 crimp both wires into one of the ¼ in stud connectors and attach this sandwiched with the two others at the ground point mentioned in #5 in the Bill of Materials section above. 6 Take the long ground you just created in #5 and connect it to #85 of the relay using a female connector. 7 Get some red wire and crimp onto one end the remaining ¼ inch stud connector. Thread this wire from the “+” terminal of the battery alongside the main bunch of wires going to the fuse buss and then connect it with a female spade to #87 of the relay. Tape everything up or whatever and then connect the stud connection to the battery. Fold the wires and relay in such a way as to lay nicely and you’re done!

I am sure there is a neater way to do this way seems to work. I did make a wire with the appropriate connector on each end so that the relay can be bypassed in case the relay fails.

Chris in Santa Cruz, CA #782