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Blown Fuse!

5K views 35 replies 10 participants last post by  Cal30M1 
#1 ·
Went for a 30 mile ride yesterday and all was going well until I jump on the freeway. I just got it up to 70 mph when it blew the fuse. Looked at all the wires I could get to without taking the tank off and couldn't see any problem. I had a spare fuse in my pocket but as soon as I put it in it blew that fuse too.
Called my AAA membership to get a tow but found out the towing my wife signed up for didn't cover motorcycles! So had to fork out for a tow bill. Apparently, I need to have the AAA "premium" tow card for motorcycles!
Hooked up my test meter to locate the short but, (of course), wasn't shorting anymore. Looked at all wires and can't find anything wrong. I did notice that my right coil was very hot but think that is because I had the key on and the points were closed that the coil fed. Wouldn't think a coil going bad would cause a fuse to blow.
I have 300 miles on the bike since putting it together with a new wiring harness. Have had no troubles until now. Appreciate if anybody has a good idea for something to check.

Gary
 
#4 ·
I had a similar problem with random fuse blowing. Turned out to be the wire to the stop light switch popped out & was shorting.
 
#6 ·
Looked at those wires also and they appear to be okay. I'm kind of concerned about the wires coming from the stator. Not sure if they are being hit by the primary chain and maybe that's causing the short. However, not sure if that would cause the fuse to blow.
 
#13 ·
I have a 76 T140V engine in my 70 Bonneville with standard ignition - points,condensers, and zener diode. I was wondering if, (since I was accelerating at and at high rpm's when the fuse blew), it's possible for the zener to go bad and short out if it got hot and then work okay when it cooled down? ---- The wire terminal connections were good and tight at both the ground and the hot side so didn't see a problem there. The diode is original from way back in the 70's but tested okay when I put it on. I actually put it in my bead blaster and took all the oxidation off it before testing it and putting it on the bike so I know it has good connections. Have you ever heard of one going bad and causing a short?.....Gary
 
#15 ·
I could be wrong about this since I'm getting old and the memory is fading fast. But..... my 71 Daytona has an AC alternator, and selenium full-wave rectifier mounted under the seat, and a zener diode out front for voltage regulation. I know that at one point the selenium rectifier failed but it failed open instead of shorted. I replaced it with a little 25 amp silicon rectifier bridge which is still in there and still works. My only point here is that the zener diode gets a lot of blame for blown fuses but a bridge rectifier could also fail shorted which would be likely to blow your system fuse. You might have a look at that.
 
#19 ·
Cal30M1:Brand New Old Stock Lucas? or brand new Lucas current manufacture? or brand new reproduction Hong Kong Harry?
Hey Cal30M1,
Thanks for responding. I don't remember what kind of rectifier I bought. It was 3 years ago that I bought it but I do remember grinding down an open end wrench so that it would fit and hold the nut under the mounting bracket so I could tighten the top nut without damaging the rectifier. The wrench was to thick to slip under the bracket. All I can tell you is the rectifier looked just like the original rectifier....Gary
 
#20 ·
StuartMac:
Btw, as your bike's a mix of oif and dry-frame years, where's the Zener located - attached to the air-filter box (oif) or to the finned heatsink under the headlamp (dry-frame)?
Hello Stuart!,
I have a 70 Bonneville with 76 T140V engine in it. The zener diode is located in the original spot on the finned heatsink under the headlight.
Do you think it's possible to be intermittent and cause a short and then cool off and be okay?
For what it's worth in this discussion, the battery has been staying charged after long rides.

Always appreciate your help. Thanks, Gary
 
#21 ·
Hi Gary,

Do you think it's possible to be intermittent and cause a short and then cool off and be okay?
As I posted above, I never like to say impossible, but a Zener heating up or cooling off almost instantly doesn't happen, so I'd say it's unlikely.

If you had a known-good Zener to swap, I wouldn't discourage but, as the problem is intermittent, you could swap the Zener and think you've fixed the problem ... 'til the next time the fuse blew. Then is it the new Zener gone wrong or the original cause, that's never been fixed ...? :(

There's never an intermittent electrical problem that wouldn't make an angel curse. Rrpita. :mad:

Hth.

Regards,
 
#22 ·
Hi Gary, July 2 is fast approaching. I've been watching the thread with great inerest. Several good suggestions so far. I have a few thoughts. As was stated intermittent problems are the very worst. It's unlikely the alternator wires or zener are the problem. Not being there in person & not seeing the colors of your wiring makes this post hard for me. I looked at wire diagram in '70 owners manual I found on Bikebiz on the sticky notes. Looks correct??

A visual inspection of great detail is the only thing you can do at this point. Thinking of the ammeter falling apart, can you see any melting or heat damage of wiring to meter. Usually on dead short that melts wiring it melts from short back towards battery. I've observed that many times. However... That is on neg. ground systems. None the less look for any heat damage to insulation as a clue. If you see melting harness could be melted inside wire jacket to red ground wire. Don't open that new harness unless you really have to. You'll see melting at exposed wires if melted.

Going over diagram since lights were off we need to look at ever "hot" circuit in detail.

Brake light sockets can cause problems, but since you were accelerating the brake should not have been depressed, but some riders reset foot is such way the brake light can be triggered by pedal so don't discount socket yet...

I'll list the circuits I noticed in no particular order.

Brown/blue fuse to ammeter.

Brown/blue ammeter to horn relay.

Brown/white to headlight switch terminal 4.

Solid white to zener.

Brown/white zener to ign switch.

White from ign switch to oil press light.

White to coils & jumper to next coil.

From one coil to the front brake light switch in brake cable.

White to rear brake light switch.

In case stop light was on wires from switches to stop bulb socket & finally socket itself. Make sure it has the correct bulb. Straight across pins with 2 contacts. Look in & make sure the fiber in socket is good & square. To really check socket wires on back side you have to take it all apart. Kind of a last resort.

Also looking a blown fuse. Do you think fuse actually blew, or did it break from vibration. Often a vibration break will leave fuse wire intact, but broken at one end or in middle with no section burned out. Sometimes impossible to tell.

If I was there could I find it? Who knows?? Only if I could see it. Hopefully you'll see the fault. Wiggle all the wires around with the key on. Really a hard problem. Start with prayer! Not kidding. If it was constant you could just disconnect circuits one at a time until fuse stopped blown. That would be much easier.

The hot coil was almost certainly from those points being closed at the time. A shorted coil would almost certainly result in misfire at times.

If anybody saw any circuits I missed feel free to post them.

Since our last ride I've covered 400 miles or so. My rear tire is bald. Had tire over a week, but no time. I've got to squeeze it in somehow.

Don
 
#24 ·
Hi Don, good to hear from you. Yes our ride date is getting close and I want to have the bike ready too. We may want to reconsider riding up Ice House road to Loon Lake. I don't think we will be able to get a cell phone signal there if something goes wrong and we'd be a long way from any service. My son and I went to Ice House Lake about 5 months ago and couldn't get a signal. So maybe your first idea would be better to go along the Mormon Emigrant Trail over to Hwy 88 and around that way.


TR7RVMan:Going over diagram since lights were off we need to look at every "hot" circuit in detail.
That's what I did and the circuit you mentioned for the horns was a place I found two wires that could possibly cause a short. So I put tape around them just in case that was the problem. However, I think I'll go take that tape back off and see if I can get the wires to short and blow the fuse. That way I'll know for sure if that was the problem.

Thinking of the ammeter falling apart, can you see any melting or heat damage of wiring to meter.
The wires to the ammeter look good with no signs of melting.
(Most of you don't know that earlier, on another ride, the bottom of my ammeter broke out of its clear plastic housing and shorted out against the headlight bulb holder and blew my fuse while driving down the freeway. I was able to fix that problem on the side of the freeway that time. Just wrapped the ammeter in a rag to insulate it and put a new fuse in. That got me home.)

Was going to take the bike back out for a longer ride tomorrow but noticed the left front fork leg is leaking at the bottom of the chrome cup that holds the seal. Looks like it's leaking by the threads where it screws on to the lower leg. Hopefully I just need to tighten that cup down a little more....Thanks for your help Don I'll talk to you later....Gary
 
#26 ·
Hi Gary, Any route you choose is fine. I've always wanted to ride Mormon Trail & 88 also. We could always coast down to a cabin with land line. No worries, between us we'll figure any problem out. Bring lots of spare fuses & tools. Bring wire diagram. I'd like to have an old school test light also. I have one. I'm not afraid. I can't wait!
Don
 
#27 ·
Hi Don, yes it will be fun and looking forward to the ride too.

Still haven't taken the bike back out since taping the wires but did remove the tape to see if I could get the fuse to blow. The fuse would not blow and with a closer look with a magnifying glass I could see no bare wires there. It was just some kind of a silvery looking dust or scuff on the wires.

I mentioned earlier that the front fork was leaking and found the chrome cup that holds the seal was lose. Tightened it up and so far no dripping but will need to see what happens after taking it for a ride.

I'll have a pocket full of fuses, that's for sure, no matter where I go from now on and as many tools as I can carry.

Weather is real nice for riding but have been working on a bracket to mount my Norton type oil filter. I'll start a new thread!....Gary
 
#30 ·
Hi Marc,

is this a mod that is highly recommended on our older model bikes?
All triples are fitted with a micropore filter as standard within the crankcases between the pump and the rest of the engine. One of the parts listed for fitment to the '74 (last) T100D's was an oil filter. I believe the late singles have a filter? So the factories were moving in that direction before they closed.

Since then, if you read the BritBike forum, thousands of owners of earlier Britbikes have fitted micropore filters without any problems whatsoever; there are several recommended filters.

Fwiw, I fitted my T100 with one of these in pretty much that position on the bike; I chose that one because it uses the triple filter element; MAP in Florida do a very similar kit.

Hth.

Regards,
 
#31 ·
Cal30M1: I don't recall the exact measurements but the big nuts you see is the muffler clamp holding it on the down tube. The smaller bolts thread into the filter base from the back of the bracket.

After tightening the filter base to the bracket and snugging the muffler clamp, rotate the unit towards the oil tank a twaat-hair counter/anti clockwise if looking down from above

If it is at the 6:00 position when "straight" then about 5:30 to 5:40 is where you need to be to clear the center stand.

THEN tighten the muffler clamp the rest of the way.

Oh and install long bits of hose before installation. You can cut it to fit later but it is neigh on impossible to get the hoses on after the filter base is installed.

Don't ask me how I know! Just save yourself some cussing!


This is on a 1969 Bonneville.

Cheers!
Hey Cal30M1,
Thanks for your post. I came up with something real close to your design. I just went down to the shop and took a picture of it. I've got it attached to a piece of a 69 frame I had laying around the shop....Gary
 

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