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No power to ignition switch. Or anything else.

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Taylorecle

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Hey first time posting here. I recently picked up a 1979 cb750 project bike. The guy had done a few things go the bike, new tank, tires, chain, but the electrical work was left somewhat of a mess. I'm not sure what he worked on exactly. But I was able to start it at first. Then yesterday I went to start it and nothing. Turn the key and no lights no power to the ignition switch, tested the coils and there's nothing going through them. The only power I can find is from the battery, and starter solenoid. If I connect the poles of the solenoid I hear the starter going, so something is connected right somewhere. But I cant figure out why I cant get spark, or power anywhere else. I've replaced the solenoid and the starter switch. Before and after still no dice. I'm looking now to see if it's a grounding issue, but at the moment everything seems fine. Any suggestions for troubleshooting?
 
Last edited:
Could be a 100 things. There is a safety on the Clutch, could be a short someplace. Get yourself a wiring diagram and multimeter and check everything. Oe, if your afraid the harness is too cobbled up, buy a new wire harness.
 
Do the lights on the instrument cluster illuminate when the key is switched on? If so, get a cheap multi meter from harbor freight and check for voltage using an electrical schematic. Start at the battery and move out from there. keep the black cable on the multi meter connected to the negative of the battery and move the positive probe to each component checking for voltage. You will have to keep in mind the function of each component. If checking a switch, the switch must be closed. Give you magnetic starter switch a few wacks with a small metal hammer. Sometimes they get stuck after sitting for a while or upon initial starting. This happened to me until I got everything cranking consistently. Also loose connections will yield inconsistent electrical power.
 
Wez_ said:
Do the lights on the instrument cluster illuminate when the key is switched on? If so, get a cheap multi meter from harbor freight and check for voltage using an electrical schematic. Start at the battery and move out from there. keep the black cable on the multi meter connected to the negative of the battery and move the positive probe to each component checking for voltage. You will have to keep in mind the function of each component. If checking a switch, the switch must be closed. Give you magnetic starter switch a few wacks with a small metal hammer. Sometimes they get stuck after sitting for a while or upon initial starting. This happened to me until I got everything cranking consistently. Also loose connections will yield inconsistent electrical power.
Click to expand...

Nothing does anything when the key is on position, theres no current going through the fuse box, I feel like it's the wiring harness, but I'm hoping its something else I'm just missing. I have a multimeter I can start troubleshooting with, I'll have to go through the web of wires and see what I can find.
 
Did you try turning the key back and forth several times?

Dirt inside the switches can make them work intermittently.
 
Excuse me butting in, have you checked the 30amp main fuse? If that is loose, corroded or blown you will have no electrical power to the entire electrical system. Shorting the terminals on the starter soleniod will crank the engine, given the battery is charged, the fuse is not part of the starter circuit.
 
Taylorecle said:
Hey first time posting here. I recently picked up a 1979 cb750 project bike. The guy had done a few things go the bike, new tank, tires, chain, but the electrical work was left somewhat of a mess. I'm not sure what he worked on exactly. But I was able to start it at first. Then yesterday I went to start it and nothing. Turn the key and no lights no power to the ignition switch, tested the coils and there's nothing going through them. The only power I can find is from the battery, and starter solenoid. If I connect the poles of the solenoid I hear the starter going, so something is connected right somewhere. But I cant figure out why I cant get spark, or power anywhere else. I've replaced the solenoid and the starter switch. Before and after still no dice. I'm looking now to see if it's a grounding issue, but at the moment everything seems fine. Any suggestions for troubleshooting?
Click to expand...
What did you find out was the problem..I have same issur
 
Start at the battery. Are the terminals clean? How do the battery cables look? Check the condition of the battery cables and contacts at both ends of the main cables (battery x 2, starter solenoid and ground). Now check the main fuse and wiring to the ignition switch for power. Check that power goes through the ignition switch when it is turned on.
 
Rod said:
Start at the battery. Are the terminals clean? How do the battery cables look? Check the condition of the battery cables and contacts at both ends of the main cables (battery x 2, starter solenoid and ground). Now check the main fuse and wiring to the ignition switch for power. Check that power goes through the ignition switch when it is turned on.
Click to expand...
For you other folks chiming in asking about this issue:

Electrical troubleshooting is how you figure this out. Eliminate the possible causes logically until you find the problem.
 
Hi, I just purchased a 1984 CB750 and I’m having the same issue sometimes it starts and has power going to the cluster and sometimes it’s dead.. Battery if 100% charged. Did you find the problem?
 
I have same problem. It turns out, there was main wire to the key switch broken, right there where it came out from under the reservoir. See the picture. The black wire should be conected to the soldered junction.
20230520_113317.jpg
 
Chris in Dorset England said:
Excuse me butting in, have you checked the 30amp main fuse? If that is loose, corroded or blown you will have no electrical power to the entire electrical system. Shorting the terminals on the starter soleniod will crank the engine, given the battery is charged, the fuse is not part of the starter circuit.
Click to expand...
Where can I find the main fuse? I have searched all over my bike and can't find any other Fuses and I'm having a similar problem.
 

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