Tips on findinf a SHORT

[TurboFarviknugn]

Had an interesting ride home from work yesterday, bike died 2 miles from home and ended up pushing it the rest of the way home ! Learned that even as a striped down bobber these bikes still have some weight to them !

Anyway today got out in the garage to figure out what is going on here, bike has been VERY reliable for over 5,000 miles as a daily rider, with scratch built wiring harness using stock Yamaha handlebar switches.

For some reason I bring this up is the 7.5 amp fuse for the pamco on the fuse box keeps popping every time I hook up the battery. I used the wiring harness below and have the short narrowed down to the orange circled area. Anyone know if a shorted coil could cause this ?



ANY INSIGHT OR SUGGESTIONS ????

 

[chugg]

Hey Turbo

I would start with the most basic stuff first. If you still have a kill switch check it first for bare wires or a shorted switch, then check the wiring and the connections. There are instructions in the tech section here on checking the coil.

Philip

 

[xjwmx]

Anyone know if a shorted coil could cause this ?

Check for continuity from both coil terminals to ground. Should be no continuity. If there isn't then the coil isn't the problem.

 

[jd750ace]

Remove the fuse, disconnect the red wire to the pamco and the coil, then check the "out" side of the fuse holder for continuity with ground. Should be none. This proofs your wiring. Make sure your stop switch is in the run position. If you find continuity, the short is in that wiring group, which now only has one component, the stop switch. To further isolate at that point, cycle the stop switch off. If the ground goes away, the short is in the wiring from the switch to the coil and pamco. This does not exclude the switch as a potential point of failure, and I would start there in this event. If you had continuity and it did not go away with the switch, the short is in the wire from the fuse holder to the switch.

 

[Brian902]

10 amp fuse.

7.5 too light perhaps.

Yamaha Motor Japan sent new bikes with 10 amp fuses in 1978.

Or loose or bad ground.
,

 

[pamcopete]

Turbo,

If your wiring is as shown in the diagram, then I would be concerned with the location of the 20 A fuse which serves no purpose other than to protect against a short in the capacitor. If that fuse blows or even just comes loose, you will lose the benefit of the capacitor and the regulator will go ape sh*#% producing a destructive high voltage which will in turn fry the PAMCO.

The 20 Amp fuse should be located in the output of the regulator before the ignition switch so if it blows there is no power from the regulator available.

Here is a similar diagram showing that.

 

[Brian902]

Pete, will your system and that coil system work on 7.5 amp fuse?

 

[pamcopete]

Brian,

When the coil is turned on by the transistor in the PAMCO it draws 13.5/2.5 = 5.4 Amps but it is only on for 120/360 = 33% of the time so the average current is 5.4 X 33% = 1.78 Amps. Because the fuse is a thermally operated device it actuates on the average current flow.

There is a protective device in the PAMCO circuit that clamps voltage spikes to no more than 18 Volts, but that device is not designed to clamp a continuous high voltage. It's purpose is to clamp the voltage spikes that come primarily from the operation of the crude mechanical voltage regulator in the earlier models.

Since the popularity of PMA's arrived over the last couple of years the most common cause of PAMCO failures with a PMA is either incorrect wiring or a defective regulator. I think as more and more PMA's are installed, we will reach a plateau in the learning curve and these failures will diminish.

 

[TurboFarviknugn]

THANKS EVERYONE for the tips, Will be headed out to the garage in the next hour to figure this thing out once and for all.

Pamcopete, no there is no fuse in that location I fixed that long ago.

 

[TurboFarviknugn]

Remove the fuse, disconnect the red wire to the pamco and the coil, then check the "out" side of the fuse holder for continuity with ground. Should be none. This proofs your wiring. Make sure your stop switch is in the run position. If you find continuity, the short is in that wiring group, which now only has one component, the stop switch. To further isolate at that point, cycle the stop switch off. If the ground goes away, the short is in the wiring from the switch to the coil and pamco. This does not exclude the switch as a potential point of failure, and I would start there in this event. If you had continuity and it did not go away with the switch, the short is in the wire from the fuse holder to the switch.

Excuse my IGNORANCE I did as you instructed, I am using a digital ohm meter I did at instructed in step 1, with the kill switch in the run position the ohm meter reads 0.00 which signifies it is making a complete loop (correct? continuity?) turn the switch to off and it reads 1 . which is open (no continuity?) I hooked up the + lead to the coil and it still reads the same way no changes. all this tells me what ?

Again I apologize for my wiring ignorance, wiring is admittedly my weak suit, guess its the Plumber in me (Hot on the left, shit goes down, payday is on Friday, no licking your fingers while eating fried chicken)

 

[XSLeo]

At some point on the wiring between the 7.5 amp fuse and the Pamco and coil the wire may have rubbed on something and is now shorting to ground. Look at the wires very carefully for and spot that look chafed. It may be a very small spot.
There have been instances that with a missing grommet in the headlight bucket has rubbed into the wire enough to short but couldn't be seen by eye but replacing the grommet fixed the short.
Leo

 

[TurboFarviknugn]

Just did 1 more test, hooked everything back up (except the coil completely out of the loop both - and + wires un hooked), put yet another 7.5 amp fuse in there, when I turned on the main power toggle switch (using toggle instead of key type switch) all is good as soon as I rotate the kill switch to the RUN position POP goes the fuse. Which tells me there is a problem in the wiring to the switch, the switch its self or the wire leading from the switch back to the......pamco (I think) I will know for sure here shortly fixing to start stripping this thing down AGAIN.

 

[TurboFarviknugn]

Removed tank seat wiring loom sheath and all zip ties figure eh, what the hell its only one more 7.5 amp fuse, hook up the battery turn on the ignition toggle....... no POP, turn kill switch to run MMmmmmmm no POP.............. give it 1 kick and WHAALAH !!! fired right up !!!! (Actually startled me !)

Now to start disconnecting and following wires to find the short, guess removing all the stuff from the wiring was enough to move the wires to where it was no longer shorting out.

Will keep ya posted !!

 

[jd750ace]

You have it narrowed down pretty good. Good work. If the loom is free of the neck and it works, check the side that was in contact with the backbone, especially where it goes past any tabs or mounts.

 

[TurboFarviknugn]

Found a small chafed area on the 2 wires going up to the switch unsure if that point would be under the clamp or not and it was sheathed in the Yamaha black plastic sleeve. Decided to replace all the way up to the switch with new wire to be done with it soldered on new eyelet connectors and will be putting it in heat shrink. Hoping this is the fix !





I have followed the wires from the 7.5 amp fuse to the switch and back to the + side of the coil should this should be the fix. (Seriously hoping so)

 

[Brian902]

The green wire is bare very near the bolt. Probably not the issue but could be tidied up.

 

[TurboFarviknugn]

ran single wire heat shrink up to plastic (after pic was taken) then encased both wires in heat shrink just inside housing all the way under the tunnel / tank area.

 

[TurboFarviknugn]

Well piss in my ear and tell me its raining !!! Got it all wired up and put back together hook the battery to the capacitor fires right up, disconnect the battery keeps running check voltage at cap bounces between 14 and 14.3 volts good let it run for a bit shut it off attempt to restart off cap no go, mmmmmmmmm go through jumping it off with the battery all good shut it down, before trying to start it again check voltage 0.00, looks like the sparx capacitor has decided to crap out after about 1 month of use. Anyone got a recommendation for something better than the sparx brand cap preferably one I could go to NAPA or elsewhere and buy off the shelf ? Hate waiting on shipping.

 

[xjwmx]

sparx brand cap preferably one I could go to NAPA or elsewhere and buy off the shelf ? Hate waiting on shipping.

Just had this thought. I think they use big caps in xtreme car stereo so you might be able to get them at a car stereo shop. The best thing is the caps I've seen there are very fancy, like chrome, fancy colors and such. Just make sure the mf (uf) and the voltage is the same or higher than what you know you need.

 

[TurboFarviknugn]

Got my new capacitors in yesterday, could only install 1 as the new one is a tad larger than the sparx.



Fired it up started and ran GREAT, took it for a spin around the block all good, then went 3 blocks all good, went out about 1 mile you guessed it BLAH, short is back !!! Had to push it home AGAIN !!!! Of course it was my last 7.5 amp fuse that I had, got more today after work, but had to go to meet the teacher thing at the kiddo's school tonight. back at it tomorrow night, some where there has to be a spot I missed on my wiring check.