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Guys got my FCR's on today so could finally fire the bike and do a couple of basic tests for my charging circuits. What is the AC voltage output I should be looking for on these older models (89 900). I am following some test procedures written about the later carbed bikes and it indicates an output around 70 volts.

I'm seeing about 45 volts coming in just over 4,000rpm and recall reading the earlier alternators are lower output than later bikes. Is this about right or do I have a problem. I have tested continuity and Ohms from the alt wires and it's all to spec. I've also removed some dodgy wire with melted insulation but I don't think it was to the stage of shorting. I've also removed the melted joiners and replaced with a heavy duty one. I did note on my bike that the alt wiring comes up the front diagonal tube to the steering head then actually turns back along the top rail back to about the rear head then turns 180 degrees back up to the steering head into the reg/rec wiring. It also had 2 connectors in the run. I've removed some bad wire and removed the unnecessary length to shorten the run directly up to the reg/rec. In all I removed 900mm or 3 ft of extra wire.

I'm just trying to nail down that my reg/rec is faulty and that the alt is OK before I go and order a new reg/rec. Battery light is still illuminating and battery is brand spanking new and showing 13 volts when idling.

FCR's are cool too except for the leaking inlet union that won't let me test ride. Wife reckons the bike sounds even meaner now than it did, still running my home baffled straight through 48mm perf tubed original style cans.

I was always lead to believe that these alternators would put out about 15Vac per 1000 rpm, so at 4000 rpm you'd expect to see about 60Vac so maybe your 45V is a little low.
However, 13V at idle is probably about what I'd expect. More importantly what does it read at over 2,000 rpm with the lights on. It should be able maintain a charge with the lights on at speeds you would ride around town, say 30 mph and 2,500 - 3,500 in 2nd or 3rd gear.
So look for a minimum of 13.6V across the battery at 3,000 rpm.
I just fitted a MOSFET regulator from a 1200 MTS to my 907ie. It is now showing 14.2V across the battery at 1500 rpm

That's not really what I want to hear. I thought the older ones were a fair bit lower but 60 compared to 70 is not much. Was hoping the issue was just the reg, don't really want to crack the motor open to deal with the alt. Is it a repair or replace kind of job.

Both the 45vac and the 13v at idle seem to low to me . 13v is near as dammit battery voltage . As Derek says voltage at the battery whilst doing 2000rpm ....3000rpm....4000rpm is more important.
Silver lining time brilliant oppertunity to upgrade. Depending on how good your contacts are it may be cheaper to get the stator rewound , although I have found mine adequate as standard and I run a 100watt headlight )

By the pictures I see online all the pre 99 stators look the same as far as fitting wise. I have come across some cheap old stock 98 ST2 stators locally that at the price make it hardly worth investigating mine further.

I know there are single and 3 phase but my understanding would be that they are interchangeable given the talk that with a 3 wire stator you can ditch the third red wire. Certainly mine is a 3 wire stator with the red cut back. I do see the ST2 in the pic is just the 2 wires.

ST2 stators are not the same. The pre 98 are smaller windings than the Paso and require a different magnet which won't fit your crankshaft. 3 phase rotors won't work at all without major changes to your crank shaft and engine cases.

For the Paso and all pre 98 belt engines there are 2 wire and 3 wire. The 2 wire stator has a higher wattage output than the 3 wire and is the stator that will work the best. If you change your 3 wire stator to a 2 wire it is recommended that you relocate your "new" regulator more into the airstream to help with keeping it cool as the 2 wire stator will put more heat into your regulator. Relocation of the regulator is a good idea anyway. It is also a good idea to improve the wiring from the battery. On my bike I just added a second wire right along side the factory wire as it was the easiest thing to do. I had my stator rewound with extra long leads and ran them straight up to the regulator which I relocated to the side of the fairing stay as on the 907 and eliminated all connectors along the way. I now have 13.7 volts at idle and 14.3 everywhere else with my dual headlights on and high output bulbs. I also replaced every other bulb in the bike with LED's which required a new flasher and changing the polarity of my brake lights and turn signals. LED's in the cluster also require changing the polarity but here it is just a matter of installing them the right direction and does not require any wiring changes.
I can now ride the bike all day long and not worry about the battery which I also changed to lithium going flat I can also now read my gauges even in the brightest sunlight

The led's and the Lithium battery came at a premium price but I feel are well worth the extra $$$

with the Lithium battery both the 907 and the 906 jump to life like never before.
The only other mod I am working on for the future is adding an oil slinger to help keep the stator cool and hopefully keep it alive for years into the future

Why do the brake and turn signals need the polarity changed.

I've already got a lithium battery too and redone some of the main wiring.

Led's are directional and opposite of a normal bulb

Its easy enough to do just switch the wires around at each bulb assembly in the rear. On the front just switch the two signal plugs

I knew the LEDs were directional but aren't the replacement LEDs supposed to be direct fit replacements. Have Ducati wired the lighting back to front with normal bulb wiring. Not a big deal for me anyway. For things like the brake/tail light and probably turns I'm going to hardwire some LED strips or panels into the loom. I don't really like the drop in replacements as they don't deal with the issue of unreliability of old bulb holders.

I presume you left the fuel indicator light alone, I read on ducatims that the fuel gauge needs the resistance of an incandescent bulb to actually make the circuit work correctly. Some guys were playing with LEDs and resistors etc but I don't think anyone worked it out.

I replaced all the dash lights in my 907 with LEDs and the fuel gauge worked just the same as it did before - tells me the tank is empty when there is still 1/4 left
I haven't fitted LED replacements anywhere else on the 907 but I swapped all the bulbs on my previous ST4s for LEDs (except the headlight where I fitted HID) and had no polarity problems.

no reason why the fuel level indicator on these types won't work with the LED. Derek I had to "adjust my level indicator" to get it to read properly. If you adjust yours be careful not to break the stops and don't ask me how I know that
There are some types of regulators that require a specific resistance bulb to work. With electronic regulators it should not be a problem.

higgy wrote:no reason why the fuel level indicator on these types won't work with the LED. Derek I had to "adjust my level indicator" to get it to read properly. If you adjust yours be careful not to break the stops and don't ask me how I know that

I'll just leave it alone. Maybe next time I'm in the tank to change the filter I'll have a look but it's no big deal as I zero the trip meter every fill and know to fill up when it's getting to about 150 miles.

higgy wrote:no reason why the fuel level indicator on these types won't work with the LED. Derek I had to "adjust my level indicator" to get it to read properly. If you adjust yours be careful not to break the stops and don't ask me how I know that
There are some types of regulators that require a specific resistance bulb to work. With electronic regulators it should not be a problem.

That's interesting as the Ms guys reckon it doesn't work as the bulb resistance is integral to the operation. Unless later bikes have a different gauge. Side note can the gauge be tested with any confidence, mine doesn't work.