Need an electric guru

[BigDick]

I put in a spade fusebox, eliminated the RLU and put in a diode I picked up from radio shack. I started the bike once the harness was all taped back up and looked pretty. The headlight came on and functioned correctly. This was last night. This morning when I was getting ready to go to work, I revved up the bike just a touch and the headlight quit. It had popped the fuse. I put in another 10 amp fuse and everything worked correctly. I twisted the throttle just to see what happened and the fuse popped. I put in a 30 amp fuse because I had no others, the headlight worked. On my way home I found out I had no headlight. I pulled the side cover expecting to see a popped fuse, but the fuse is good, I pulled the bulb and it seems blown, there's soot on the inside but I have continuity through the filaments (this denotes a good bulb correct?). The bulb plug seemed like it may have melted a bit, so I pulled the seat and gas tank to see if my harness had melted anywhere else. I had taped the harness and then put the replacement diode in and taped over that. the tape seemed to be heat damaged slightly where the diode was, but not anywhere else. I pulled the tape off to look and the diode has localized soot around it (3/8 of an inch). I checked with my multimeter, all three of the leads in the headlight plug are grounded somewhere. When checking the fuse block the hot side is not grounded, but the other side is grounded. Am I going to have to take the tape off of the whole harness again? Where should I start? I'm going to check on getting a new factory diode from yamaha now. Pictures to follow in a little while.

There is a possibilility that I put the diode in the wrong direction.

[b.walker5]

aaaaarrrgggghhh

First of all NEVER, i repeat NEVER increase the fuse size above the rated current of the circuit, If it's rated correctly and it's popping then you have a fault. You might as well put a 4 inch nail in it. A fuse is in a circuit to protect the cable, not whats on the end of it. By increasing the fuse above the rating of the cable you run the risk of melting the insulation and causing your bike to burn to the ground in the event of a short. Maybe while your on it , it has happened

As to your fault, it sounds like you definately have a short in the system somewhere, although the fuse blowing only after the revs build is a mystery. If removing the RLU is the only thing you've done then you definately need to recheck that work. I'm not familar with that mod so I can't comment further at this stage, except to say that a diode is a one way device, in that current will flow in one direction only. So if your lights work at idle then that would tend to suggest the diode is installed in the correct direction. You mentioned that you got the diode from Radio Shack. Is it rated correctly for the current load?

Sorry, missed the bit about the new fuse box. Does it have seperate circuits or is it a common rail type, where it's designed to have only one 12v supply and the fuses are connected together internally in the box. If it's this type then its the wrong one. If it has seperate circuits then check and recheck your connections to be sure you have not installed it incorrectly.

[BigDick]

The fuse box is the individual type, it's the one TC provides. I know putting in the 30 amp fuse was stupid, but i'd hoped for a temporary fix so Security Forces wouldn't have an excuse to give me a hard time (I was on a Air Force base). When I changed out the fuse box I had each pair of wires taped together, then only cut them and attached them one set at a time to be SURE they wouldn't get mixed up. When i did the RLU bypass, I had a print out of the article with the diagram right in front of me so I would be sure it was routed correctly. I did have to peel about half of the tape off of the wiring harness to find the diode but i didn't cut any of it, just unwind. My bike came with the factory yamaha fairing, so it had a couple extra "stock" wires on the front end, not to mention an extra foot or so of wires, I cut those off and removed aobut 8 inches of wire and then spliced with waterproof crimp connectors. I did these also one connector at a time so the wires wouldn't get crossed.

[tw1980]

Hey Dick I'm not familiar with this mod but I'm confused as to why you replaced the factory diode inside the harness.I hope I'm not barking up the wrong tree but looking at the schematic for an sg I think that circuit is just to turn on the relay that supplies power to the RLU.Was the original diode defective?If the replacement diode shorted the ac generator would supply ac current to that circuit possibly blowing the ten amp fuse.When you substituted the 30 amp fuse the replacement diode may have opened then no power would be supplied to that circuit.I would start by rechecking all your work.Also like before mentioned what is the current rating on the replacement diode?Two or three diodes hooked up in parallel will increase the the current rating.If you still can't get it working I may have some time tomorrow night I'll try to find the RLU mod.Terry

[BigDick]

for whatever reason when I removed the fairing I couldn't get the headlight to work. I had some dingbat "fix" it for me, he spliced from a "keyed" wire to the green wire coming from the headlight. When I installed the blade fuse box I decided to fix it correctly. Since I didn't know if it was the RLU or what I went ahead and did the RLU bypass, after that I did a bit of research on here and found out about the diode, when I found the diode one lead was seperated from the ceramic body. I checked at the local Yamaha today, the diode from them will be $11 and 3-4 days. Pretty extravagant considering I got 2 from Radio Shack for $1.50 *shrug* Like I said I guess tomorrow I'll look through the wiring harness again.Here's the link for the RLU removal/bypass.

[BigDick]

Here's the front and back of the package the diode came in. All I know about diodes is that they're a "check valve" for electronics, they allow electricity to flow in one direction but not the other. This is the only 12 volt diode they had at radio shack. I figured for a dollar and a half it couldn't hurt to try.

[b.walker5]

Okay, the original diode is used as a gate valve in the circuit that allows current from the generator to switch on the headlight relay once the bike is running. The diode is there to prevent a reverse current flow to the generator through the relay coil. Two things are immedialtly obvious to me, 1 is that the original diode is likely to be rated considerably higher than 21 milliamps and I'm fairly certain the original wont be a zener diode. Under some conditions Zeners will allow current flow in both directions and they need to dissapate heat while operating. In your example it is dissapating 1 watt of heat. Still not completely sure what is blowing your lighting fuse however because from what I can see the diode is only in the relay coil circuit, not the lighting power circuit. Did the lights get real bright just before the fuse blew?

[randy]

The original diode is not a Zener. Zener diodes are used for voltage regulation. Go back to radio slack and slap the counterperson, the get a pack of 1N4001 diodes, 50V 1A. Install it with the cathode (striped) end toward the headlight. That will eliminate the diode issue.

[tw1980]

Yeah what Randy said a zener won't work.

[boyat68]

As Randy said a zener is normally used in the reversed bias position to regulate voltage to a protected circuit. However it can be used in a forward bias position, but it acts like a common diode and the characteristics of your data block indicates that it is only a 12V @21ma, which is way too small for your alternator output. If you check the specs of the alternator it is 14.5 V 20Amps at 5000 rev/min. bigger is better.

[BigDick]

Did the lights get real bright just before the fuse blew?

I couldn't tell what the lights did before it all blew, this was in the middle of the day.

Go back to radio slack and slap the counterperson, the get a pack of 1N4001 diodes, 50V 1A. Install it with the cathode (striped) end toward the headlight. That will eliminate the diode issue.

I'll check at radio shack if they can order the correct one for less than Yamaha. If they can help me out I'll report back. If not I'll still report back and order the one from Yamaha.

Like I had said, the only thing I knew about diodes is that they act as a gate valve. I figured that 12 volts would be correct since our bikes are a 12 volt system. Thanks for taking the time to explain to me everyone.

[randy]

They should have the 1N4001 in stock. You can go with a higher dissipation, say 2A or 10A, just don't go lower.

[DiverRay]

I figured that 12 volts would be correct since our bikes are a 12 volt system.

That is the STATED volt rating. The DC volts are actually almost 15, and the AC volts, that the diode needs to contend with, can be 35 to 40 volts. You probably have a short in the wire instead of a diode. once you remove the small diode, and put in the one Randy said, you should be OK. I would also look to see if any of the wires got hot and melted together. I had that problem on my old daily ride. The main power line melted, and was just making contact with the ground wires in the harness. Took me about a month to find that one!

[oldnortonrider]

First of all NEVER, i repeat NEVER increase the fuse size above the rated current of the circuit, If it's rated correctly and it's popping then you have a fault. You might as well put a 4 inch nail in it. A fuse is in a circuit to protect the cable, not whats on the end of it. By increasing the fuse above the rating of the cable you run the risk of melting the insulation and causing your bike to burn to the ground in the event of a short. Maybe while your on it , it has happened

As to your fault, it sounds like you definately have a short in the system somewhere, although the fuse blowing only after the revs build is a mystery. If removing the RLU is the only thing you've done then you definately need to recheck that work. I'm not familar with that mod so I can't comment further at this stage, except to say that a diode is a one way device, in that current will flow in one direction only. So if your lights work at idle then that would tend to suggest the diode is installed in the correct direction. You mentioned that you got the diode from Radio Shack. Is it rated correctly for the current load?

Sorry, missed the bit about the new fuse box. Does it have seperate circuits or is it a common rail type, where it's designed to have only one 12v supply and the fuses are connected together internally in the box. If it's this type then its the wrong one. If it has seperate circuits then check and recheck your connections to be sure you have not installed it incorrectly.

"b.walker5"; could you say more as to why the rail type fuse block would be the wrong type for a replacement. (And anybody else that might have an opinion about this..............)

[Geezer]

I have a large bag of 3 amp diodes good for up to 250v. You don't by a diode based on it's minimum voltage. I'll send you one for the cost of postage.

Geezer