Wiring - only the horn works!

[gabster]

1983 PK50 bought as a box of bits. Scooter now starts and runs OK but none of the lights work. The only electrical device working is the horn. I’ve checked the wiring several times and just can’t find what’s wrong. Is there a separate earth somewhere that isn’t part of the wiring loom? If it was a fault from the stator or rectifier, why would the horn work? 

[jbcollier]

Going to need more information. PK50 scoots came in a wide variety of equipment levels. It could just have a headlight, taillight and horn. Or it also could have one or more of the following: stop light, park light, regulator, signals, battery, electric start, etc. Stators came in four pole/two coil, four pole three coil, and six pole. You scoot is coming up on 40 years old. Is it still stock? If not, what mods have been done?

Don't know the answers? Then you'll have to look, take clear pictures and post them. Need to see the stator, stator wiring, wiring under the tank, wiring under the LH cowl, headset photos, photos of the wiring in the headset.

[gabster]

It has indicators, headlight, taillight, rear brake light and horn - no battery.

[jbcollier]

Does it have a four pole or six pole stator?

[gabster]

6 Poles. I,ve been using VX51T diagram which matches my wiring. I’m not good with electrics - prefer oily things 😁 Looks like Horn circuit is separate to everything else though. 

[jbcollier]

Does this look about right?

[gabster]

Yes that’s the one

[jbcollier]

Do you have a multimeter that show AC volts?

[jbcollier]

If the horn is working, then your stator is at least putting some power. That's the blue wire from the stator. The blue wire goes:

stator - junction block - handlebar switch - horn

At the horn it turns to yellow and goes:

horn - handlebar switch - junction block - regulator

So we know it is getting to the horn and handlebar switch. You need to test if it is getting to the AC regulator.

The AC regulator has three terminals and these wires on each one:

Black = ground - should be a good ground to the chassis, engine and headset. The body of the regulator should be grounded as well.

yellow = main power feed - should be 10-ish volts AC

green and gray wires = power out to the rest of the circuits - should be 10-ish volts AC

Test all that and let me know what you have.

[gabster]

Sorry, excuse my ignorance. Do I unplug wires from Regulator and put probes on Regulator spades or on the wires?

[jbcollier]

Leave everything plugged in when doing the above tests.

[gabster]

Yellow & Green/Grey both read 12.3 (fast idle)

[jbcollier]

That's a little high and may lead to blown bulbs, BUT, we have power, which is excellent. Now we go through each circuit one at a time and sort the issues. Let's start with an easy one: the brake light circuit. It works like this:

regulator - gray wire - brake light switch - blue wire - brake light bulb - tail light housing ground - chassis ground

We have power at the regulator and the brake light switch is a pain to get at so start at the brake light bulb. Take off the tail light lens and check for power at the blue wire when the brake pedal is depressed at idle. If you have power, then either the bulb is blown or you don't have a good ground. If you don't have power, take out the brake pedal and check the switch.

[gabster]

Have 11v when pedal is pressed. Bulb looks ok, all connections look clean and fit snuggly. Will put a new bulb in and if that doesn’t work I’ll try and add an Earth

[jbcollier]

Check for voltage on the metal bulb socket. If there's the same 11v then you have a ground issue.

[gabster]

Getting somewhere at last - using battery charger rather than running the engine. Adding an Earth to Rear Lights has go them working. Headlight and Park Lights work too. I still have no Indicators. Put the meter on Front Indicators and there’s no power getting to either. Looking at Switch, the pink wire is only connected by a couple of strands - I will have a go at resoldering it tomorrow. Also, on the short harness from the indicator switch to junction box, the red wire doesn’t look too well soldered at the ‘bullet’ I’ll sort these out and hopefully it’s sorted. 😊 Once all works on battery charger, if it then doesn’t work from engine then I guess we have stator or rectifier issue?
Should there be a separate ground wire from the frame to the engine like on Lambrettas?

[jbcollier]

Fitting a separate ground is a good idea. I fit 'em to my scoots.

The most common failure point in the signals, after bulbs and grounds, is the indicator relay. You can bypass it to check if the wiring, switch and bulbs are ok. Just power the white wire off the relay to test the system.