Bad rectifier...?

[Alan H]

Yes you can get stop/tail LED bulbs.
They are directional in that they can only be connected so that current flows in one direction.
I got some for the 550 and hopefully will see them working in the next few days.
CLICKY - lots of different types. I got white LEDs as the reflector is red (same as a white bulb.)

[Lorenzo]

do not know if this post as been deemed solved, in case not, since I am going through the R/R drama with the GS - which as a long history of frying stators due to the way it was wired from the factory, with the wire going to the headlight not being wired trough the regulator, and with the particula tipology ot the latter - there is a couple of check you could do, with a multimeter (the higher the quality of whose, the more accurate the reading);

the first might actually be on the alternator side, checking that it outputs the maximum alternating voltage, stated in the manual, from the three wires, taking the reading at the Rpm again stated in the book, on the three wires alternately ie wire 1 and wire 2, wire 1 and 3, finally wire 2 and 3; reading with multimeter set on alternating voltage;

Once you are assure the alternator is outputting regularly, than you can than check the R/R itself, by taking it out of the system and taking an Ohmic reading between the five wires (the three from to the alternator and the battery and the mass hearth one as per values stated in the man, which varies from engine to engine;

If this test is passed, you wanto to look for voltage drop on the wire (orange?) to the right switch block, and from it to the lamp itself, with the two meter probes in series with the wire, resistance should be (I'm doing a bit of guesswork, cause I do not have the man around) between 0,3 and 1 hom, but reference the manual;

You can improve on the connection itself by taking the earth off the lamp and bringing it to the frame;

I do not know the rate of failure of the complex R/R stator in this particular model, but if high as in the GS series, you might want to do the best mod you could on the electric comparment, by replacing the stock R/R whose internals are built in parallel (the SCR or other type of resistances) in so dumping a huge unwanted voltage back to the stator on each cycle, transforming the energy into heat, with adverse effects on the shunt themselves and on the stator, which is required to work overtime on each cycle, by replacing it with a series regulator, which only requires from the stator the exact amount of current it need on the particular load, ligh on/off, high beams on/off, horn on/off) so everyone is working easy and cool;

If you want to follow this course, I might be more specific, issuing the complete checks;

ciao

[Vintageman]

Be careful. If your idle is too low these old Alt designs may not keep up no matter what reg. you use.

http://www.madelectrical.com/electrical ... orks.shtml" onclick="window.open(this.href);return false;

I like the old electro/mechanical ones, run cool, and handle the occasional electrical surge without breaking.
These ones were at the end of their time: all kinks sorted out. I would have no problem putting in another mechanical one or using the one I have. I admire them .

Now a H4 headlight seems like a must if you want to ride at night. Has to fit and look OEM IMO

Sure, the LEDs are real modern. But, concerned the younger than I cop if behind me will question why such a modern bike stinks so bad. “here is your fix it ticket sir” At best, if you don't try to explain

[jabcb]

http://www.madelectrical.com/electrical ... orks.shtml" onclick="window.open(this.href);return false;

Now a H4 headlight seems like a must if you want to ride at night. Has to fit and look OEM IMO

Interesting link.

Here are pics of my T500 with the H4 headlight upgrade.
Looks a little different with the H4 headlight upgrade.
The headlight rim is a little more rounded & the headlight lens is a lot less convex.

stock:

H4 upgrade:

[Coyote]

You guys must know something I don't. The H4 halogen is a great upgrade for a GT750 or GT550. That's because they share the same headlight bucket. HOWEVER, the GT380 bucket is nearly an inch smaller. There IS NO upgrade for this machine. I went round and round when building RedZone (GT550). I used a 380 headlight bucket because the smaller headlight went better with the overall package. There is NOTHING that will fit this bucket period. You are stuck with the stock lamp forever. I looked for months and found no suitable replacement
The bottom line is don't Be recommending an H4 as a replacement for the 380. IT WON'T FIT!

[jabcb]

To install the GS-L series headlight, you also need to use the GS-L series headlight rim + misc parts.

Chrome headlight bucket, part # 51810-33600, is used on:
GT185 & GT380
GS550L, GS750L, GS850GL & several other GS-L series bikes.

These GS-L series bikes have a smaller diameter headlight than the regular GS-series bikes.

Figuring out that the GS-L series headlight fits the later GT250s & T500/GT500s is a more convoluted process.

For my 1975 T500M, I installed NOS GS-L series parts (headlight lens, rim, etc.) in the headlight bucket that was on the bike.

If you look closely at the headlight rims in my two pics, you can see that they are slightly different.

[Vintageman]

jabcb,

Nice bike and your headlight came out well. It must work well too

I think OEM are called 6 3/8" Dia?

And, there were different versions of OEM as time went on... I think they kept upping power.
25W/25W ?
30W/25W ?
40W/30W ?

And from jabcb pointing us to that old post. I saw this too ->
http://store.candlepower.com/638inhe.html" onclick="window.open(this.href);return false;
And says this ->
Additionally, some bikes may not have the electrical capacity to properly lite a 60/55W H4 lamp, and it is suggested that you use the "Low Wattage" version located 8022LR plus 45/45W.

Probably this has already been looked into?

You have to be careful of higher power bulbs in older twins. Newer twins better not sure what changed (would think something with Gen. not sure haven’t spent the time to sort out)

[jabcb]

I saw this too ->
http://store.candlepower.com/638inhe.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
And says this ->
Additionally, some bikes may not have the electrical capacity to properly lite a 60/55W H4 lamp, and it is suggested that you use the "Low Wattage" version located 8022LR plus 45/45W.

Probably this has already been looked into?

You have to be careful of higher power bulbs in older twins. Newer twins better not sure what changed (would think something with Gen. not sure haven’t spent the time to sort out)

I'm using a 45/45W H4 on my T500. I would be inlined to first try a 35/35W H4 on a GT250.

[yeadon_m]

I was fortunate to buy my used GT380B in 1978 already with a dealer option 'Cibie' H4 reflector (it may be 6" or a bit smaller, whatever stock was) which looks stock. 35y later I scored another one new for 99p (the old one had some lifted slivering near the parking lamp) and its in my bike now!

The lamp is 60w/55w H4 and though dip stinks at night, the HI is plenty bright enough to ride fast through country lanes.

The 550/750 both have easy to get and low cost H4 reflectors which fit the stock rim / bucket easily. Not ridden the 550 at night, but the 750 is fine (OK ish on dip) and blazingly good on Hi. No worse anyway than any single headlamp modern bike. Which is to say, not that good. Now my eyes are not what they were, I definitely appreciate the twin H4's in my car!

Cheers,
Mike

[JFISHSOLEVIBE]

Thanks a lot for the detailed replies fellas. I'm ordering one of the Oregon replacements to simply get that out of the way.

In pertinence to my low idle, I am using a Newtronic ignition and recently got rid of the old resistor style plugs and caps as replaced with resistorless type. That made a noticeable difference in idle performance. I was surprised!

[JFISHSOLEVIBE]

So I checked out the battery... Reading 13.2 static and about 14.6 at revs. Seems within tolerance? Battery has apparently been charging as I haven't had it on a charge since late last year!

However, I'm still noticing big fluctuation is the lights when used. Noticed that when turn signal is operated the headlight dims with each blink of the flasher, as does the neutral indicator light and instrument back lights.

Any ideas?

[jabcb]

Your GT380 has a Kokusan or Nippon Denso alternator.
The output curve for your alternator is shown on page 18 of http://www.ozebook.com/compendium/suzi/suzidata1.htm

The alternator doesn't have much output at idle.
The bike is using battery at idle, so its normal for the headlight to dim a bit when the turn signal flashes.

Back in the 70s it was pretty common for a bike to need 1.5k to 2k rpm for the alternator to start charging the bike.

[Coyote]

got rid of the old resistor style plugs and caps as replaced with resistorless type. That made a noticeable difference

+1 Did the same thing on my 550. Much fatter spark with a lot more 'snap'. Resistor plugs were designed to cut down on radio interference. That was decades ago. Not an issue with the modern electronics of today.

[JFISHSOLEVIBE]

Yeah, coyote I'm really surprised with the difference it in combination with the electronic ignition made.