• NOTICE: The owner of this website and GTMotoCycles.com completely lost his home on the morning of January 8th in the L.A. Wildfire Storm. Most of his neighborhood is gone, and a few friends were killed along with their pets. The GTM SHOP and STORE are functioning normally, but we DEMAND EXTREME PATIENCE on orders as we are a SMALL business and Todd usually has his hands on nearly every order before it goes out. You can find more info on a post named L.A. Wildfires in the USA section. Our heart and best go out to everyone effected in this horrific disaster.
  • Ciao Guest - You’ve landed at the ultimate Guzzi site. NEW FORUM REGISTRATIONS REQUIRE EMAIL ACTIVATION - CHECK YOUR SPAM FOLDER - Use the CONTACT above if you need help. New to the forum? For all new members, we require ONE post in the Introductions section at the bottom, in order to post in most of the other sections. ALWAYS TRY A SEARCH BEFORE STARTING A NEW TOPIC - Most questions you may have, have likely been already answered. DON'T BE A DRIVE-BY POSTER: As a common courtesy, check back in and reply within 24 hours, or your post will be deleted. Note there's decades of heavily experienced Guzzi professionals on this site, all whom happily give endless amounts of their VALUABLE time for free; BE COURTEOUS AND RESPECTFUL!
  • Be sure to see the GTM STORE link also above for our 700+ product inventory, including OEM parts and many of our 100% Made-in-SoCal-USA GTM products and engine kits. In SoCal? Click the SERVICE tab above for the best in service, tires, tuning and installation of our products or custom work, and don't miss our GT MotoCycles® (not) art on the BUILDS tab above. WE'RE HERE ONLINE ONLY - NO PHONE CALLS MADE OR RECEIVED - DO NOT EMAIL AND ASK QUESTIONS OR ASK TO CALL YOU.
  • There is ZERO tolerance on personal attacks and ANY HYPERLINKS to PRODUCT(S) or other competing website(s), including personal pages, social media or other Forums. This ALSO INCLUDES ECU DIAGnostic software, questions and mapping. We work very hard to offer commercially supported products and to keep info relevant here. First offense is a note, second is a warning, third time will get you banned from the site. We don't have the time to chase repeat (and ignorant) offenders. This is NOT a social media platform; It's an ad-free, privately funded website, in small help with user donations. Be sure to see the GTM STORE link above; ALL product purchases help support the site, or you can upgrade your Forum profile or DONATE via the link above.

Perplexing electrical issue - advice welcomed!

Julian Sudano

Julian Sudano

Tuned and Synch'ed
GT Contributor
Joined
Jul 25, 2021
Messages
67
Reaction score
18
Location
Los Angeles, CA
Hi All

My 1984 V65 SP has a really irritating electrical issue. The Italian electrical gremlins have finally struck!

When I turn the ignition on, and when the bike is running, I get no dashboard warning lights: no Oil Pressure light, Generator light, Neutral light, Hi Beam light, etc. As I rev the engine, the generator light comes on and stays on until the engine returns to idle. I also get no headlight, even with the light switch on. My brake light doesn't work when using only the hand lever.

This is the odd part though. When I brake, using both the foot pedal and hand lever simultaneously, ALL the dash warning lights illuminate!

I followed some previous advice on this forum and pulled apart the 15 pin Molex connector under the tank, and was able to restore the dash light operability, by playing with #4 pin which connects the front and rear brake circuit pressure sensors and dash lights. However, I pulled the front of the bike apart to grease the yoke bearings, and the issue came back. I was able to restore the dash lights again, by repeating this, but only briefly. It's now a permanent condition.

I'm at my wits end here, as I hate messing around with automotive electrical systems as I don't really understand them well. I have spent hours with my multimeter checking continuity on all of the circuits that seem to be interconnected, but haven't been able to find any faults. I've pulled apart the LHS switch gear - Light Switch, Flash/Horn Switch - but can't seem to identify any issues. One anomaly is that the head light will illuminate when the Flash Switch is pushed.

If anyone has any suggestions, hints or advice I would be grateful!
 
I'm not familiar with this bike but Is it possible to disconnect the generator and its associated regulator/rectifier and just have it on the battery, the reason I say this is when you rev the bike you have issues with the gen light. Either of those 3 could be compromised and putting an earth/12volts where is shouldn't be. Also check you have good earths with zero ohms where applicable. Bad earths in lamp fittings can cause all sorts of weird problems. Try to use an analogue meter and not a digital multimeter as the later has such a high input impedance it can give erroneous readings. You can even use a small light bulb with a couple of wires attached to check voltages and earths.
 
Is the bike stock? At this age somebody may have been messing with the wiring so it won't necessarily match the wiring diagram. Look for sections of the wiring that have been electrical taped. Often with an old wiring harness, pulling on it to connect/disconnect things can trigger other problems caused by poor repairs.

I would start methodically, pick one item (say the oil pressure light), When the bike is switched on, you should get 12V on that wire. Trace it back on the positive side and check you're getting 12V and it switches on and off with the key. Also chase the earth back, on my bike the earths are shared between a few of the warning lights although mine has been heavily messed with so I don't know whether that is right or not. Your earths likely need a good cleanup - undo the bolts and make everything shiny before re-assembly.

Electrical problems on cars can be a real pain, the V65 is a bit simpler (but not much simpler) than a car but it will be time consuming.
 
Not knowing your bike specifically .... But 53 years of fighting electrical problems on my own bikes can allow me to state with confidence that 95% of bike electrical problems are due to either a battery that can not supply sufficient current under load (solved with a Battery Tester, not a voltmeter), OR a loose or corroded ground wire, either to the frame or battery negative post. Smackeyacky's advice is good, never mind his weird screen name!

Lannis
 
smackeyacky said:
Is the bike stock? At this age somebody may have been messing with the wiring so it won't necessarily match the wiring diagram. Look for sections of the wiring that have been electrical taped. Often with an old wiring harness, pulling on it to connect/disconnect things can trigger other problems caused by poor repairs.

I would start methodically, pick one item (say the oil pressure light), When the bike is switched on, you should get 12V on that wire. Trace it back on the positive side and check you're getting 12V and it switches on and off with the key. Also chase the earth back, on my bike the earths are shared between a few of the warning lights although mine has been heavily messed with so I don't know whether that is right or not. Your earths likely need a good cleanup - undo the bolts and make everything shiny before re-assembly.

Electrical problems on cars can be a real pain, the V65 is a bit simpler (but not much simpler) than a car but it will be time consuming.
Click to expand...
Thanks - I will dig into that shortly. Took a break as it was doing my head in! I'm now wondering if it is the handlebar switch gear as I had that off, and checked it all out, and now it Lights warning light on the dash does work, but the lights don't come on! It appears that the wiring has not been messed with at all...
 
smackeyacky said:
Is the bike stock? At this age somebody may have been messing with the wiring so it won't necessarily match the wiring diagram. Look for sections of the wiring that have been electrical taped. Often with an old wiring harness, pulling on it to connect/disconnect things can trigger other problems caused by poor repairs.

I would start methodically, pick one item (say the oil pressure light), When the bike is switched on, you should get 12V on that wire. Trace it back on the positive side and check you're getting 12V and it switches on and off with the key. Also chase the earth back, on my bike the earths are shared between a few of the warning lights although mine has been heavily messed with so I don't know whether that is right or not. Your earths likely need a good cleanup - undo the bolts and make everything shiny before re-assembly.

Electrical problems on cars can be a real pain, the V65 is a bit simpler (but not much simpler) than a car but it will be time consuming.
Click to expand...
Thanks mate - I did check the Oil Pressure circuit a while ago but didn't get any voltage with the ignition switch On, or with the engine running. The positive side of the circuit would be the "supply side" yeah? OFf to muck around with the beast again now.
 
Thanks to all who weighed in on this irritating issue!

Happy to let you all know that I have fixed the problem! After taking your advice Smackeyacky, I traced the Oil Pressure circuit back to the supply, at Fuse # 3. All looked good, but I thought I may as well test the fuse for continuity, and loe and behold, when I put the prongs for the multimeter on either end of it, I saw the smallest of sparks at the supply side of the fuse. Turns out the fuse, which along with the other 3 in the fuse box I had replaced when this issue started, was faulty despite looking fine, until I pulled it out to inspect it.

At least I can now ride with the confidence of knowing that I have given the electrical system a thorough going over.

Fuse 1.webp
 
You must log in or register to reply here.
Back
Top