Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Johnny4428 on October 24, 2020, 03:06:31 PM
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Here’s my dilemma, I have removed wiring harness removed all covering and inspected tested and repaired one or two connections. With harness now back on bike and all connected again I still have the same issue regarding heating of switched black wire and fuse glowing when ignition is on. If anything it is worse after my intervention. The only thing is I’m quite sure the problem is not with the harness. With the black wire disconnected from voltage regulator all is fine. When I test between live spade connector on regulator and frame I get open circuit. So am I being stupid or is there a problem there because to connect live wire to regulator is like putting a live wire to frame or earth. Wish I had another regulator to try on bike. Help!
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Possible short on white wire to field coil as black goes to white to excite generator
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Is that between white wire and ground Bryan? Just tested and white wire is open to ground!
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White wire should go to ground via the field coil if its open circuit its broken somewhere and could short intermittently
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Thanks Bryan, yes no resistance between white wire and frame of bike, I will follow wire back to coil tomorrow. Thanks for your help I will report back findings.
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If its the 750 check the connections in the lead to alternator, there is a point where the white an green from field connect via bullet connectors and these get hot and melt the insulating sleeves sometimes, same on 500/550 but there is no oil sealing shaped rubber bit to deal with.
Is this a standard reg or an aftermarket combined unit?
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Yes Bryan it’s a 750 with possibly original regulator. I have had the cover off it and it just looks like new on the inside. That lower bullet connectors look as if they have been subjected to a bit of heat.
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Those connectors could be your problem, the regs are normaly bulletproof but the everything, specially me, is getting older
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Removed cover and generator the day, so getting 2.5 ohm between end white wire and casing. Nothing obvious, seems to be ok between 8 terminal plug and female connector.
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Should be infinite resistance white to casing and low resistance white to green.
Maybe white has been trapped and has partially shorted
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Long distance electrical fault finding is like shoveling sand in a hurricane!!!
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Yes Bryan I was thinking it’s not easy for you, I’m staring at it with a meter and still scratching my head. I have put it back together replacing some of the connectors. The reading from white wire at reg to frame about 1.8 to 2 ohm and between green and white wires at reg about 2 ohm as well. I didn’t see any shorts to frame but I didn’t remove coil from casing. I’m still getting a bit of warming at main fuse but dare I say not as bad as before, not right either. I am in time going to completely strip and restore bike so wonder if I shouldn’t waste any more time looking for something that I will probably find through dismantling and inspection.
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Just found this on recent post. Sounds as though field coil resistance too low drawing too much current.
"ALTERNATOR FIELD COIL: using a multimeter set on Ohms scale, verify the resistance between the WHITE and GREEN. It should be about 7.2 Ohms. Also check the coil isn’t grounded; ie measure between the White and battery -ve. ... it should read infinity."
That is measuring at field coil connections.
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When doing resistance checks on low readings first you need to touch the meter probes together, in theory the reading should be zerp but it never is and you need to note this reading and subtract it from any measured reading you get.
2 ohms is very low for a field coil what do you get across all 3 pairs of yellow wires, block connector pulled out
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Thanks Cliff I will try these tests tomorrow.
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Thanks Bryan, yes that readings are the “net” value. I think the meter is shite to be honest, just put a new battery in it that’s probably doubled the value, and that was a cheap battery from tesco.😂 I will carry out more tests tomorrow with another meter.
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Is this the one with a 3 fuse box or the single fuse?
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Three fuse..
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OK, those fuse holders loose their "springiness" enough to cause a high(er) resistance contact to fuse which causes heating and in the states has even loosen the solder connection to the wire making the problem worse.
On the US site Mark Paris(hondaman) makes a plug and play blade fuse conversion to replace them.
With meter =ve probe on battery check +ve voltage at both ends of main fuse both with ign off and on, if there is a measurable difference the fuse holder is duff
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Thanks Bryan I was having a bit of trouble getting the fuse to connect at times I put it down to just old dirty connections same as rest of bike. I will try that today. Central heating pump to change first. Success of that depends on isolation valves.
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Thanks Bryan I was having a bit of trouble getting the fuse to connect at times I put it down to just old dirty connections same as rest of bike. I will try that today. Central heating pump to change first. Success of that depends on isolation valves.
Take the fuse box off and remove the rear cover. You will be surprised what you find in the back of those sometimes ;)
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0.4 volt difference between these contacts with ignition on.
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0.4 volt difference between these contacts with ignition on.
With kill switch on or off ? With kill switch on you will lose volts to the points ;)
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Checked as Cliff suggested between green and white connections on field coil and meter read infinity. Also checked between white and battery negative which also gave infinity.
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Indeed trigger will try again.
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Looks like that’s where my .4 volt went to coil circuit.
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Half a volt drop across the fuse suggests bad fuse to clip contact and/or wire to contact in back. There should not be any drop there as its just a straight connection and should have zero resistance
As this is under load i suspect this is you fuse warming problem.
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Thanks Bryan, what about the readings between green and white field coil wires going to infinity? As Cliff suggests should be resistance of around 8 ohm. I did test with another multi meter this morning.
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Yes there should be contiuity between white and green wires to the field coil, best to check first as close to coil as possible then work back towards electric panel retesting at each junction
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Think I have cracked now Bryan. I am at least able to switch on without fear of something smoking. Next job fire up and check charging etc. Can’t get neutral signal to panel though. Checked bulb and it’s fine, also power to it is good. Not important at moment, got oil pressure light.
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Again possibly a bullet connector, is there power on black wire to bulb? If so try grounding the wire at the neutral switch, if light works its switch if not break in wire from bulb to switch
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Thanks Bryan, yes grounding out from switch activated light, so I will check wire from switch to light panel if it’s ok I guess it will be switch.
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Good continuity between switch wire and headlight connection, think must be the switch.
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If grounding it at switch put light on the switch is duff
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Yes Bryan, I will take it out and see if it can be revived until I replace.
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Hi guys just studying some of the pics I took last week and noticed this, possible short and definitely can’t be correct position of this retainer.