Author Topic: Strange 750 wiring problem..  (Read 1342 times)

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Offline 754

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Strange 750 wiring problem..
« on: August 19, 2019, 06:24:46 PM »
 First off, I am more interested at this point, if anyone has experienced this.
 More info will be added.
 Basically I turn my key on, I now often I have no idiot lights, then after 30 seconds to a minute they come on, not full bright.. turn the kill switch of full bright comes on. If I wait around two minutes it will get to full bright with kill on. Then I can kickstart it.  A few days ago full  bright and it starts right away, but not when bike is hot after running.

  Sat morning, full on bright, lights on , horn worked,  can hit horn and brakes stayed running, 20 minutes later  can't run with lights on, brake light can stall it at idle , horn won't work for a few seconds..... hitting horn and brake light same time will kill engine EVEN at 3K.

 So I did 900 miles this weekend, and it's hard to start nearly every time.
 Before I say what I did check, let me know if you have seen this happen before
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline toma

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Re: Strange 750 wiring problem..
« Reply #1 on: August 19, 2019, 07:00:36 PM »
Bad or intermittent bad ground. Problem then becomes - to find it. Good hunting.

Offline 754

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Re: Strange 750 wiring problem..
« Reply #2 on: August 19, 2019, 07:27:03 PM »
 I have checked a few of the grounds and fixed some..
 However I have suspected a ground cable someone made up to battery, it has a ring terminal with a hole, the sure goes in the hole and is held with a setscrew, and I been thinking, it is not ideal..
 Good call I hope, thanks.
 Several things I have tried and one was redoing the harness ground, have resulted in turning the key on to check and it appears fixed, only to have problem reappear hours later.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline maxheadflow

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Re: Strange 750 wiring problem..
« Reply #3 on: August 19, 2019, 07:49:48 PM »
Sounds like the charging system is getting weak. Possibly the battery. Do you have electric start?

Offline scottly

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Re: Strange 750 wiring problem..
« Reply #4 on: August 19, 2019, 08:15:56 PM »
Stock fuse box? Check for a poor/dirty connection at the fuse clips, and any sign of overheating, including the back side.
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Offline 754

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Re: Strange 750 wiring problem..
« Reply #5 on: August 19, 2019, 08:33:23 PM »
 Changed fusebox, changed regulator.
 Don't use electric start, has a small battery...
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline scottly

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Re: Strange 750 wiring problem..
« Reply #6 on: August 19, 2019, 08:45:26 PM »
How about the ignition switch?
Don't fix it if it ain't broke!
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Offline RAFster122s

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Re: Strange 750 wiring problem..
« Reply #7 on: August 19, 2019, 09:01:17 PM »
Sounds like a short for it to slowly increase in brightness the idiot lights. Could be ground problems in addition to the short. Sounds like a black wire short in brake and horn circuits or bad ground in those circuits since brake application or horn application are causing the failure to become critical. Handlebar wiring OK?

David
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Offline bryanj

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Re: Strange 750 wiring problem..
« Reply #8 on: August 19, 2019, 09:09:36 PM »
Had bad contacts inside key switch, getting hot softens fibre/plastic base so contacts receed a bit and you get weak contact therefore volt loss hence dim getting brighter as contact gets a bit better with heat.
You can take the switch apart and clean contacts plus make sure all "buttons" in base are slightly proud
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Offline 754

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Re: Strange 750 wiring problem..
« Reply #9 on: August 20, 2019, 12:27:24 AM »
 Yeah, I changed key switch,  but have to open this one up to make sure. I can hotwire it at the  plug end, to eliminate it being the switch.
 Stator connections under chain cover will be cleaned this week as well.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline pjlogue

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Re: Strange 750 wiring problem..
« Reply #10 on: August 20, 2019, 01:51:12 AM »
Had this happen about 40 years ago.  It was the contacts inside the ignition switch.  In my case there was dirt and grease inside the switch.  This (I think) caused a high resistance.  As the resistance point got hot the grease woulld melt/flow so more contact was made.  I opened the switch up and cleaned everything and all was well after that.

-P.

Offline scottly

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Re: Strange 750 wiring problem..
« Reply #11 on: August 20, 2019, 08:42:44 PM »
I had an issue with my K1 switch years ago: the metal "cup"? that holds the plastic part with the contacts was loose where it was crimped to the switch housing. The contacts themselves were fine, but the loose "cup" didn't allow proper contact. Ended up compressing the cup against the housing, and J-B welding it firmly in place. No problems since then. ;D
Don't fix it if it ain't broke!
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Online PeWe

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Re: Strange 750 wiring problem..
« Reply #12 on: August 20, 2019, 11:04:32 PM »
My K6 had ignition switch problem early 80's. I cut the wires close to the switch and connected needed wires with a hidden switch ( flip arm type, no key) under the tank. No harm done on main harness.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline 754

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Re: Strange 750 wiring problem..
« Reply #13 on: August 21, 2019, 08:10:07 AM »
 Dealt with my ignition switch, re did my battery ground.. might be better, not riding it far enough to really tell.
About the 6th time I thought I found the problem.
 
 Scott the loose switch to housing, I knew mine was loose. On Sunday I stoped for a drink, on a hill so I could start it.. 95 degrees. Turn switch it freewheels.  Back fell off.. get out my tape , tape it back on. Then I got bright idiot lights, ahh I think.. it's got to be the switch, fix it when I get home.. but ten minutes later, same old problem..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline MauiK3

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Re: Strange 750 wiring problem..
« Reply #14 on: August 21, 2019, 09:07:21 AM »
Some times wire can get corroded back away from a connector and have high resistance. Maybe get a digital volt meter and check resistance of the various ground wires to see if you have one that's border line high.
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Offline RAFster122s

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Re: Strange 750 wiring problem..
« Reply #15 on: August 21, 2019, 10:14:12 AM »
Black wire rot is not unheard of... Tough to find on areas with multiple paths as you have to be able to isolate a single wire to find it.
David- back in the desert SW!

Offline 754

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Re: Strange 750 wiring problem..
« Reply #16 on: August 21, 2019, 09:04:22 PM »
 I may have found it . Will know tomorrow , if it's what I found today, it's sort of embarrassing.
 To add insult, I gassed up on the way Home and I did something sorta stupid , I think...
Has to push it 1/2 mile home, slight uphill most of the way. . Second time I pushed that far since Saturday morning. Ugghhh.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Online PeWe

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Re: Strange 750 wiring problem..
« Reply #17 on: August 21, 2019, 09:41:57 PM »
I'm very curious about the problem. If an easy problem, misplaced fuse?

Frank, you'll have a reason for a nice test ride when you have sorted it ;)
That's the charm with these bikes, always something to test after repair or modification.

I like cheap restaurants in smaller villages making the test ride a special event.
« Last Edit: August 21, 2019, 09:43:29 PM by PeWe »
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline scottly

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Re: Strange 750 wiring problem..
« Reply #18 on: August 21, 2019, 10:05:57 PM »
I don't think tape would be an adequate fix for a loose ignition switch? ;) I had to use strong spring clamps to compress the contact springs while the JB weld set up...
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline 754

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Re: Strange 750 wiring problem..
« Reply #19 on: August 21, 2019, 11:45:01 PM »
The key portion with the  threads is diecast I think.  It has two round pins sticking out. The ignition switch is in a steel can. Can fits over  diecast portion,  then the 2 round pins get peened.
 So I re-peened these  holding the steel can to the keyswitch, then reassembled the ignition guts in the can, after cleaning, then crimped the can in 3 spots to hold the plastic with the contacts in place.
  Works fine , thought that may be my problem.. but no such luck.  :-\    :-\
« Last Edit: August 21, 2019, 11:47:00 PM by 754 »
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Kevin D

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Re: Strange 750 wiring problem..
« Reply #20 on: August 22, 2019, 04:41:03 AM »
Frank, I had this intermittent problem with my round plug ignition switch:
 The switch itself was ok. When plugging it in to the main harness, one of the wires on the main harness got pushed back in the main harness receiver plug. The switch wire and the harness wire were touching, but not with the intended M-F engagement and too much movement would open the circuit.
 I got my smallest screwdriver and pushed the offending wire back into the plug, taped the daylights out of it and it's been good for 35000mi/17yrs.
 
71 CB750 K1
104,000 miles
Original Owner
———past———
70 SL100/125/150
70 Candy BlueGreen CB 750 K0
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Offline 754

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Re: Strange 750 wiring problem..
« Reply #21 on: August 22, 2019, 05:41:41 PM »
 With fingers crossed, I cautiously say, I think  I have it fixed..
 So my battery it appears was losing a cell, and it got worse yesterday.
 But when It would not start ,  I found something I overlooked. .stupidly..
 No secret, I am not fond of electrics nor maintainence thereof.

So as it did not start , I lift the seat , and check fuses,  make sure battery connections are tight.
 The positive wire is heavy , goes to solenoid, about 3 inches long, had cleaned it a few times. And beside it, coming off it is a short run of red/white, with a bullet connecter, and I think...hmmm ..main connection into the wire harness, and not been checked..  So I get it apart, green, grotty,  corroded.. really bad.. So I think I found the sputtering smoking fuse... faaaacccckk.
 Still  had to push it  home... got a battery today.. finally might be good.. fingers crossed..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline RAFster122s

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Re: Strange 750 wiring problem..
« Reply #22 on: August 22, 2019, 07:03:09 PM »
I hope you have found it Frank. Sounds like it is very likely that you have done so....

David
David- back in the desert SW!

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Strange 750 wiring problem..
« Reply #23 on: August 22, 2019, 08:15:34 PM »
and now you will be headed south? I'll be there about 6pm.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline 754

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Re: Strange 750 wiring problem..
« Reply #24 on: August 22, 2019, 08:59:13 PM »
Nope can't get down there. .  Probably go to northern Wa near the border, ride the backroads.. a bit.,
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way