Author Topic: electrical failure AHH! '75 cb750 (Read 2396 times)

1974blaze · « **on:** October 26, 2009, 09:00:03 AM »

ok, i have read all of the posts, and there are many, describing this exact situation, but i was riding along and then NOTHING. no electrical at all.

this happened once last summer and i installed a new ignition, all better until now.

i'm guessing it's the main fuse right? but my fuse box has 3 fuses that read 5A 7A 5A from top to bottom and the "look" good. besides, the main isn't a 5 or 7 right? it's like a 15 or 30???

so, i have followed the + off of the battery and it goes to a cylinder looking thing (not the fuse, right? it's kinda big, like a quarter in diameter). but i'm not finding anything looks like a fuse. could be the new ignition, so which wires do i jump to bypass?

so frustrated, please help oh gurus of the tarmac.

-blaze

J.Webster Designs · « **Reply #1 on:** October 26, 2009, 11:16:43 AM »

i had some lovely gremlins hiding in my fuse box. similar situation as you would happen. i would be riding and boom dead in the water.... if i jiggled the fuse box around a little bit it would come back to life..... I ended up replacing the fuse box for blade style fuses and all is well now. to this day i couldn't tell you what was wrong with that fuse box. i tried everything to diagnose it but could never figure it out.

If i was you i would bust out the multi-meter and start at the battery and find where your positive wire goes dead. just follow down that harness testing connections in succession and when you find where the line goes dead you should know what part is causing you problems. good luck with it all. i hate diagnosing electrical.

TwoTired · « **Reply #2 on:** October 26, 2009, 11:45:25 AM »

Got a Multimeter?
Skills to use it?
Whatever it is, it's a mechanical problem. But, you can use electricity to find it.

Hush · « **Reply #3 on:** October 26, 2009, 11:53:45 AM »

Pull those "good looking" fuses and give the fuse holders a good clean up with a small wire brush then coat them in dielectric grease.
Most of our SOHC4 bikes also have that "main fuse" down by the solenoid which also can become a non conductor so give that a birthday too.

If you hadn't recently installed a new ignition I would have been naming that as top suspect.

GammaFlat · « **Reply #4 on:** October 26, 2009, 12:02:46 PM »

The glass fuses lie! They fail in the ends where you can't see the failure. I too have replaced with a bladed unit and as Tony the Tiger would say, "it's greeeaaat".

If you want a cheap test, buy some Wrigley's gum (or steal some foil from the kitchen). Wrap you fuses in foil and then put 'em back in. I believe the top one is the one failing you (and it should be 15amps btw). Do not be tempted to leave in the foil when the bike starts.

mystic_1 · « **Reply #5 on:** October 26, 2009, 05:16:33 PM »

Quote from: 1974blaze on October 26, 2009, 09:00:03 AM

so, i have followed the + off of the battery and it goes to a cylinder looking thing (not the fuse, right? it's kinda big, like a quarter in diameter).

I'm betting that your cylinder looking thing is an inline fuse holder. Grip the ends right where the wires go in, push in (together) and twist. It should turn 1/4 turn and then release, springing apart in two halves, revealing a fuse.

mystic_1

Gordon · « **Reply #6 on:** October 26, 2009, 05:42:55 PM »

Quote from: mystic_1 on October 26, 2009, 05:16:33 PM

Quote from: 1974blaze on October 26, 2009, 09:00:03 AM
so, i have followed the + off of the battery and it goes to a cylinder looking thing (not the fuse, right? it's kinda big, like a quarter in diameter).

I'm betting that your cylinder looking thing is an inline fuse holder. Grip the ends right where the wires go in, push in (together) and twist. It should turn 1/4 turn and then release, springing apart in two halves, revealing a fuse.

mystic_1

You sure that's not the starter solenoid? That's where the positive battery cable goes to.

mystic_1 · « **Reply #7 on:** October 26, 2009, 06:32:52 PM »

You might be right, depends on if he meant "like a quarter, in diameter" or "like 1/4 inch diameter"

mystic_1

1974blaze · « **Reply #8 on:** October 26, 2009, 07:45:19 PM »

i meant like a quarter dollar and i think it is the solenoid. i've been looking for a main fuse nearby but haven't found squat. so if the main fuse is not in the fuse holder, where would it be? and what would it look like? and if the fuse at the top is 15A, which makes more sense, why does it say 5?
BTW thanks everyone for the help, i'll try it all.

Don R · « **Reply #9 on:** October 26, 2009, 07:53:11 PM »

I think the top one should be 15amp, not 5. that could cause it to blow.

mystic_1 · « **Reply #10 on:** October 26, 2009, 07:55:49 PM »

Does the fuse say 5 or does the fuse holder say 5?

Someone may have put in the wrong fuse.

BTW, any corrosion on your wires? If the battery terminals or any of the connections at the solenoid or ground strap have corrosion it can cause intermittent problems like this. Clean them up with a brass bristled brush.

mystic_1

Hush · « **Reply #11 on:** October 26, 2009, 07:59:07 PM »

Previous owners of these bikes set traps, all my fuses were 20amp when I got the bike!
The main fuse may not look much like a fuse if it is the original "spanner" fuse, it is a thin grey metalic strip held in place by two screws and should be right next to the solenoid.
Once removed it actually looks like a tiny 1 inch spanner...hence the name, many bikes have had this up graded to an "in-line" fuse in a plastic fuse holder or to the newer bayonet fuses commonly found in cars.

mystic_1 · « **Reply #12 on:** October 26, 2009, 08:06:45 PM »

Spanner fuse:

mystic_1

1974blaze · « **Reply #13 on:** October 26, 2009, 09:29:35 PM »

ok, i'll look for the spanner. any chance that there is NO main fuse, like the PO removed it. there is a suspicious yellow and red stripe wire lurking in the area. is is not connected to anything. could it all have been re-routed to not have a fuse?

mystic_1 · « **Reply #14 on:** October 26, 2009, 09:31:51 PM »

Possible. Got pics?

mystic_1

1974blaze · « **Reply #15 on:** October 26, 2009, 09:44:21 PM »

i'll take some tomorrow. seems prudent.

ekpent · « **Reply #16 on:** October 27, 2009, 07:22:02 AM »

You did double check though the connection where the ignition switch plugs into the harness ?? Let me down once.If your ignition is up in the handle bar area can make wires a little short and stress connecter with sharp turns.

1974blaze · « **Reply #17 on:** October 27, 2009, 01:02:31 PM »

i did check the wires. one of them had power. now it doesn't

i don't get that at all. here's a pic.

mystic_1 · « **Reply #18 on:** October 27, 2009, 02:27:13 PM »

"Solenoid right?" = Correct.

"Should power be coming out of here?" = only when you push the start button. the solenoid is a big switch. When you feed power into the small wires, it connects the large wires together.

"Fuses top to bottom" = 15A, 7A, 5A ( I think )

"Red + Yellow Wire" = I think this is your problem. Red+Yellow carries voltage from the rectifier to the fuse block. Find where it's broken off and fix it.

Got a wiring diagram? There are some good ones in the tech section of the main SOHC4 website.

http://www.sohc4.net/index.php?q=node/135

mystic_1

TwoTired · « **Reply #19 on:** October 27, 2009, 03:36:22 PM »

Those fuse clips are ugly tarnished. At LEAST, polish any part of it that makes contact with the fuse ends.

Yel/red stripe is from the starter switch. It ought to connect to the solenoid itself, one of the small wires.

mystic_1 · « **Reply #20 on:** October 27, 2009, 03:47:19 PM »

Oops misread diagram. Red+white from rectifier join with red in the harness which takes power to your fuses. TT is absolutely correct (but of course) that the Red+Yellow runs from the starter button the the solenoid. A problem with red+yellow should not lead to the "whole bike shuts down" problem but the fact that it's broken means the other connections in the area should be considered suspect.

mystic_1

1974blaze · « **Reply #21 on:** November 20, 2009, 11:03:22 PM »

yeah! well, thanks to all, but whoever said clean up the corrosion and the the fuse boxes are crap, you win. here's the final results. tested everything and got cozy with the multimeter and the wiring diagram, learned lots. i suspected the ignition, so i tested it. 12v, 8.3v, 4v, 2.5v then i kicked the dangling fuse box, 12v. that thing was GREEN on the back when i pulled it. so i jumped it with some wire and all was lit up like a x-mas tree. took the box apart (i know many are saying under their breath, replace the damn thing with blades) and scrubbed, dremeled, sprayed, soaked, soldered, and reinstalled. all better!
the fuses for the record were just fine. but, the fuse box had been installed upside-down and looks to me to be from a F-bike not a K from studying the various diagrams. different config/amps. but now it's coming on winter and painting time. polished casings till 1am the other night, just to repay the bike for working again without costing me money.
thanks to all, great answers and suggestions as always.

Spanner 1 · « **Reply #22 on:** November 21, 2009, 03:14:40 PM »

Congrats on fixing the fuse box!.....I didn't see anywhere you have changed the Main fuse to a 15 amp , hope you have or bike will quit again !!! ( Tail=5A, Headlight=7a ).

1974blaze · « **Reply #23 on:** November 22, 2009, 02:48:13 PM »

yup, did that. thanks.

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Author Topic: electrical failure AHH! '75 cb750 (Read 2396 times)