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cb750 rectifier

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ogre:
hi all on my 1970 cb750 just bought new battery before connecting it checked to see if i was getting a drain connected positive terminal and put meter between earth on battery and earth lead off the bike not connected got 12v its a new wiring loom disconnected rectifier no volts so took the sleeving off the wires of rectifier must of got hot in the past and melted so seperated the wires connected it back up getting 12v again am i right in thinkin the rectifier is shortening between the red and green through the rectifier or travelling straight thru the diodes in it
any help would be appreciated
thanks

LesterPiglet:
It's hard to understand what you have done there without putting a few full-stops in. I'm not sure what you have connected to what.
If you have the + terminal of the battery connected and your - not,  then put your tester between the - battery terminal and the earth lead you will read 12v.

ogre:
sos for the grammar.yes i have the negative disconnected ignition off and meter between negative on the battery and earth strap to me it should read 0 volts. i did this test a few years back on my 750 supermagna cos everytime i come to the bike the battery was flat .i found i was gettin about 5 volts reading on the meter finally traced it to the starter solenoid it was shorting inside it.

Lobo:
Don't think you're performing this test correctly. As you described it, I'd expect zero volts reading with the ignition switch OFF (because open circuit)...  & 12v with switch ON, because you're now reading the potential diff across the battery.

What you should be doing is setting your meter scale to AMPS (10A range), and connecting it as you describe... ie in between the battery +ve & red lead, OR .... -ve battery & earth strap. (Ie in series).

The following all engine not running... and assuming all switches, INCLUDING the kill switch, in good working order. Any current drain less than 50mA is basically OK, tho' zero is the goal.

Remember any non-standard mods... eg alarm fitted, side stand warning switch, lights perm ON, ... whatever... ensure these circuits are disabled, eg alarm fuse out, side stand up, bulbs removed... what have you.

With the ignition switch OFF, you should have a zero Amp drain (assuming you've no alarm, etc) If you have got a significant reading its likely your ignition switch is faulty... try disconnecting it at its loom plug.

With the ignition switch ON, there will now be a 'drain', according to which circuits are 'ON'.

With ign ON and all switches OFF (including the kill switch) only the alternator field coil should be energised, and this will be drawing about 1.6Amps. This is normal.

If you now disconnect the Alternator loom plug (Yellow/Yellow/Yellow/White/Green) you will isolate the field coil, and should now see a '0 Amp' drain.

If still registering something then there's a current leak somewhere... perhaps indeed signifying a defective rectifier.... in which case now disconnect this loom plug.

If still registering a current drain try now isolating the voltage regulator .... simply detach the black lead.

If still registering a current drain there's a problem outside of the charging system, and you'll have to start disconnecting more items to 'zero' that ammeter...

Hope this makes sense / is of use.

Simon

ogre:
thanks for the reply but with the ignition off and my meter between the earth of the bike and battery earth i'm getting 12v am i right in thinking something is giving the ground side a 12v supply which it shouldnt.it was an auto electrician who told me this a few years ago. could be doing it wrong but funnily enough about 12 months ago our fork lift truck kept draining the battery over a couple of days i did the same test on it sure enough got a 10v reading across the disconnected earth.the flt guy couldnt find the fault we ended up putting a kill switch from the battery cured the problem sos for goin on a bit. 

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