Electrical System Modification

Some CBX750s suffer problems with the electrical system, the voltmeter reads anywhere between 14 and 16 volts, and with the headlights off it nearly always is sitting on 16v and some even with the headlights on. The manual says that anything over 15v indicates an electrical overload.

As far as the group has been able to determine, this problem is due to the regulator incorrectly reading the battery voltage. After going all the way through the loom and back to the regulator, the added resistance of the loom causes the regulator to believe that the battery is 1 volt below the true battery voltage.

This can cause 2 problems. First the battery is constantly being charged and this shortens the life of the battery. Second, fuses blow for no apparent reason or your headlights blow more frequently than they should. My CBX went through 5 in a year.

The solution however is relatively simple. We provide a short-cut so that the regulator sees the correct battery voltage, direct from the battery; rather than the incorrect voltage from the loom. We use a relay to stop the battery being drained by the regulator.

You will require a standard headlight electrical relay , a couple of short pieces of wire (4 × 18” pieces will be fine for under seat installation and 4 × 8” pieces for under side cover installation), a selection of wire connectors, a soldering iron and wire cutters.

For the brave (or those who simply want to see what we’re doing), here’s the schematic diagram:

In Image 2 you can see we have elected to extend the wire by using connectors rather than cutting and soldering. This was done because we only had my bike as a test and it seemed to work there but when I start working on someone else’s bike I tend not to make assumptions and wanted to be able to reverse the installation completely. The wiring here is from Viking’s bike which was suffering from the 16volt syndrome before we started.

Note the picture displays the black wire connected to a Yellow/Red wire. Really you should not do this, try to use the same color wiring.

Connect the extension wire from the Red lead on the block to pin 87 on the relay.
Connect the Black lead from the loom to pin 85 on the relay.
Connect the new piece of wire to where the black wire was on the connector block and to pin 30 on the relay.
This is an image of a completed assembly using all the right colored wires.

Just to show you that we can do it the right way.
This unit was mounted under the Side Cover.
Here you can see that Viking elected to have his under the seat.
List member Alan has come up with an interesting solution to the problem – rewire the bike! Or at least parts of it. I won’t bore you with the details, but by adding larger wires and additional ground paths, Alan has solved the problems he was having with low voltages and bad grounds. View the details here in his write-up (28KByte Adobe Acrobat file).