Electrical Problem (2013)

[h-dDrifter]

Hey Folks, Brand new here. I am a technician in a motorcycle shop and generally specialize in Harley Davidson. However, I have a customer who recently discovered a "72 750 Commando while clearing out his late father-in-law's estate. It is in beautiful condition and has a great patina since it has been locked away since 1978. In an attempt to get this bike running, we have removed and cleaned the carbs, cleaned and readjusted the points and plugs but when we tried to install a battery, we started getting sparks from the ground post as if there were a short to ground and began to blow fuses. After bypassing the fuse, the wire to the zener diode on the right side of the chassis began to smoke. As I really hate to dismantle this pristine wiring harness chasing a short, does anyone have any ideas where to start looking for this problem?

 

[L.A.B.]

Welcome to the forum.

Are you aware the electrical system is positive ground?

http://britmoto.com/manuals/Manuals/750_man.pdf

 

[Old Bloke]

O my goodness, the Harley guys are trying to torch the Commando :shock:

No seriously, +1 what Lab says, (and for the record, I've been into my local Harley dealership for bits and bobs, rubber mounts, nuts and bolts, ignition switches etc, and they could not have been any more helpful to me when I said it was for a Norton, so no offence meant)

 

[batrider]

Bypassing a fuse is idiocy. Don't care what brand of anything you are working on.

 

[bluto]

Bypassing a fuse is idiocy. Don't care what brand of anything you are working on.

True...what IS safe when tracking down a short is to replace the fuse with a 12V bulb as it will limit current (i.e. a 50W bulb would not conduct more than 4 amps or so). If there is a dead short the bulb will glow brightly until it is eliminated. It does sound like maybe the battery was connected negative ground as was said, but if not a bad zener diode or 1MC capacitor is possible.

 

[Torontonian]

Technician... please do not eliminate a fuse when playing with vehicle electricitys be it positive or conventional negative ground. Enjoy. Rectifier could be toasted.

 

[concours]

Hey Folks, Brand new here. I am a technician in a motorcycle shop and generally specialize in Harley Davidson. However, I have a customer who recently discovered a "72 750 Commando while clearing out his late father-in-law's estate. It is in beautiful condition and has a great patina since it has been locked away since 1978. In an attempt to get this bike running, we have removed and cleaned the carbs, cleaned and readjusted the points and plugs but when we tried to install a battery, we started getting sparks from the ground post as if there were a short to ground and began to blow fuses. After bypassing the fuse, the wire to the zener diode on the right side of the chassis began to smoke. As I really hate to dismantle this pristine wiring harness chasing a short, does anyone have any ideas where to start looking for this problem?

Duhhhh.... just put the smoke BACK IN!!! :roll: :lol: :mrgreen: :idea:

On the off chance this isn't a troll, OP, you need to contact your MMI instructor, mention to add a 60 seconds of mention covering history and positive ground.

 

[mikie3117]

don't feel bad. I recommend looking up a podtronics unit and installing per spec. Positive ground systems are pretty rare.
Good luck.
Mike

 

[Torontonian]

The rectifier can't handle that kind of abuse , Podtronics opportunity ?

 

[DogT]

If the zener got hot enough to smoke, it's toast, pun intended. I hope we haven't scared him away.

Dave
69S

 

[baz]

i must admit i did this once when i was 18 years old on a BSA A65 connected the battery the wrong way round i have never forgotten that lesson !!

 

[eatpasta]

True...what IS safe when tracking down a short is to replace the fuse with a 12V bulb as it will limit current (i.e. a 50W bulb would not conduct more than 4 amps or so). If there is a dead short the bulb will glow brightly until it is eliminated.

It looks like Bluto hasnt been active in quite a long time but I just wanted to throw out there, that this was a great tip for me.

As a newbie to the site and Nortons, I had been chasing down a fuse-blowing short now for a few weeks and scratching whats left of my hair away.

After reading this, I rigged up a bulb that will plug into the fuse holder and in 30 mins I tracked the short down to the amp meter inside the headlight.

The bike now runs stronger than ever as I suspect it had been on its way out for some time

Sorry for reviving an old thread but I figured if it helps someone else out, it may be worth it.







....and for the record, yes I believe you did scare him off



gotta have thicker skin than that to hang around a bike forum though....