78 Maxi Tail Light Gremlin

Why doesn't my tail light work? It just quit. So I replaced the bulb. Still nothing. Tried another new bulb. Nothing. Checked bulbs on a six volt battery, and they're fine. Checked power with a test light at tail light, and it's good, but as soon as I install a bulb, no power to it.

If I connect my test light to the neg and pos terminal of the actual tail light socket I have power, but if I install a bulb I do not. If I check for power with a bulb installed, test light will not light up. I don't know actual voltage, as my cheapo Amazon multi meter decided to take a shit. The separate brake light works fine. I have checked ground connections at wiring block and frame.

What's the dealio?

Re: 78 Maxi Tail Light Gremlin

Have you tried bending the tab that connects at the base of the bulb up? sometimes that gets bent back and doesn't fully connect to the bulb

Re: 78 Maxi Tail Light Gremlin

> Mike Boyd Wrote:

> -------------------------------------------------------

> Have you tried bending the tab that connects at the base of the bulb up?

> sometimes that gets bent back and doesn't fully connect to the bulb

Yeah, I wasn't lucky like that. I even attached alligator clips to the contacts, and touched to the bulb, and it won't light. But if I touch the test light to the clips, there's power. And if I leave the test light connected and on, and touch the bulb to the leads, the test light goes out. WTF?

Re: 78 Maxi Tail Light Gremlin

Hmm that is super weird... my bet is:

1. the grey coil is fried. i don't know why this happens but it was taught to me early on in mopeds and i have seen it being the case. it's not putting out enough to power the bulb, but the test LED has much less draw. if you swap the brake light power to the tail light assembly, does the bulb light up?

2. less likely, but there could be a smudged ground somewhere in the assembly where the bulb goes in. Doesn't fully explain the test lead tho

Re: 78 Maxi Tail Light Gremlin

> Mike Boyd Wrote:

> -------------------------------------------------------

> Hmm that is super weird... my bet is:

>

> 1. the grey coil is fried. i don't know why this happens but it was

> taught to me early on in mopeds and i have seen it being the case. it's

> not putting out enough to power the bulb, but the test LED has much less

> draw. if you swap the brake light power to the tail light assembly, does

> the bulb light up?

>

> 2. less likely, but there could be a smudged ground somewhere in the

> assembly where the bulb goes in. Doesn't fully explain the test lead tho

Well, I think No. 1.

If I swap the brake light power to the tail light wire on the assembly, the tail light bulb lights fine, thus further eliminating a ground issue in the assembly and affirming a grey tail light coil issue.

Dammit.

Thanks for your troubleshooting/diagnosis guidance!

Re: 78 Maxi Tail Light Gremlin

Check the wiring block where the tail light coil lead ends and make sure that's a good connection, and check wiring from the block, through the frame and under the fender for any potential damage. If that all looks good it's likely the coil.

Re: 78 Maxi Tail Light Gremlin

Yeah, that all looks good.

Also, like I mentioned, I switched the brake light/tail light wires at the wire block, and the tail light lit up with the brake lever, so the wire path is okay.

I'm gonna switch out a different stator plate assembly and see what happens.

Re: 78 Maxi Tail Light Gremlin

Removing just the grey coil and replacing it with another one is actually pretty easy too if you like your timing/points as is

Re: 78 Maxi Tail Light Gremlin

Yeah, I tried another stator. Same problem. So I switched back, because it ran better with the OG ignition.

What sends the power to the tail light? It doesn't run thru the headlight switch, yet it's supposed to come on with the lights. How? I thought I had a grip on these electrical systems, and yet...

Re: 78 Maxi Tail Light Gremlin

Isn't the ignition grounded through the taillight on puchs?

Re: 78 Maxi Tail Light Gremlin

> Aaron Blair Wrote:

> -------------------------------------------------------

> Isn't the ignition grounded through the taillight on puchs?

No, Vespa does but not Puch.

One thing to keep in mind is that coil is only outputting for a single filament 6v5w running light BA15s bulb. Is that the bulb you're using?

Re: 78 Maxi Tail Light Gremlin

The trick would be to swap the grey coil out for a green brake light coil, ground one of the leads and run the other to the tail light and you can use a 6v 10w bulb there too

Re: 78 Maxi Tail Light Gremlin

Yeah, I'm running the correct bulb, from treats. I like the idea of a brake light coil in its place. I'll mess with it more tomorrow.

Re: 78 Maxi Tail Light Gremlin

I've been trying to troubleshoot this issue a little this afternoon. I don't believe the taillight coil is bad. Here's why.

1) When I first began having an issue, it was my headlight that wasn't working, NOT my tail light. I investigated and found that the speedometer light bulb tabs were bent, allowing the positive lead to touch the speedometer mounting bracket, grounding it out, thus direct grounding the headlight circuit. Important! The taillight was working at this time. I straightened the tabs, and the headlight came on as normal. Problem was, I no longer had a taillight. Thinking maybe I had a bulb with a loose filament, I bought two sets of brand new bulbs. New bulbs made no difference.

2) When I put a completely different stator assembly in, there was no difference.

Currently, I have all new working bulbs, and the original stator installed. Just for kicks I removed the speedo bulb, and touched the two wires together, and the taillight comes on, but headlight goes out. How come the taillight comes on when I short the headlight out?

Re: 78 Maxi Tail Light Gremlin

from what i gather, the headlight coil when switched on induces the tail light coil to make power, thats why theres no wiring to it, your magnetic fields are flipped.

Re: 78 Maxi Tail Light Gremlin

Do you still have the headlight switch? What happens when that's switched off? I really want to know what's going on here...

Re: 78 Maxi Tail Light Gremlin

Yes, I still have the factory square plastic switches. With the switch off, I have no lights, tail or head. With the switch on, I have headlight only. Unless I direct ground the headlight circuit, then the headlight goes out and the tail light comes on.

Pat, if the activated headlight coil excites the taillight coil, why is it only doing it if the headlight circuit is shorted?

Where does the taillight gray coil get its ground from? If it is in series with the headlight coil it would have to get its negative from the headlight circuit. If it's in parallel, it would have its own, right? They are in series, correct? Am I just missing a bad ground somewhere?

I really want to know what's going on here too!

Re: 78 Maxi Tail Light Gremlin

I must be overthinking this. It's something simple that I'm missing. It's mopeds, for crying out loud. Mopeds are dumb.

Re: 78 Maxi Tail Light Gremlin

> Seth B Wrote:

> -------------------------------------------------------

> I must be overthinking this. It's something simple that I'm missing.

> It's mopeds, for crying out loud. Mopeds are dumb.

Mopeds ??? LOL

Re: 78 Maxi Tail Light Gremlin

> P D Wrote:

> -------------------------------------------------------

> > Seth B Wrote:

>

> > -------------------------------------------------------

>

> > I must be overthinking this. It's something simple that I'm missing.

>

> > It's mopeds, for crying out loud. Mopeds are dumb.

>

> Mopeds ??? LOL

I know, PD. I know.

I'm married; I'm reminded daily.

Re: 78 Maxi Tail Light Gremlin

> Seth B Wrote:

> -------------------------------------------------------

> > P D Wrote:

>

> > -------------------------------------------------------

>

> > > Seth B Wrote:

>

> >

>

> > > -------------------------------------------------------

>

> >

>

> > > I must be overthinking this. It's something simple that I'm missing.

>

> >

>

> > > It's mopeds, for crying out loud. Mopeds are dumb.

>

> >

>

> > Mopeds ??? LOL

>

> I know, PD. I know.

>

> I'm married; I'm reminded daily.

I just say 'I don't know nothin' . It's a lot easier than getting too technical . ;)

Re: 78 Maxi Tail Light Gremlin

> Mike Boyd Wrote:

> -------------------------------------------------------

> The trick would be to swap the grey coil out for a green brake light

> coil, ground one of the leads and run the other to the tail light and

> you can use a 6v 10w bulb there too

I've been thinking about this, wondering if it would burn out your ignition coil?

Re: 78 Maxi Tail Light Gremlin

> Erik Thalman Wrote:

> -------------------------------------------------------

> > Mike Boyd Wrote:

>

> > -------------------------------------------------------

>

> > The trick would be to swap the grey coil out for a green brake light

>

> > coil, ground one of the leads and run the other to the tail light and

>

> > you can use a 6v 10w bulb there too

>

> I've been thinking about this, wondering if it would burn out your

> ignition coil?

Elaborate...

Re: 78 Maxi Tail Light Gremlin

Would putting the 10w green coil where the 6w gray coil is in the stator if it would have any effect on the ignition coil blue wire that it sits next to?

Re: 78 Maxi Tail Light Gremlin

Sorry got that backwards would it have any effect the light yellow wire coil?

Re: 78 Maxi Tail Light Gremlin

This is really starting to piss me off! So I started from scratch. I bought a new multi meter. I removed the taillight assembly, and checked all wires and connections. Perfect. Then I unwired the entire wiring block. Checked all connections. Checked all grounds. Removed headlight assembly and checked all wires, grounds and connections. Then I removed the grey taillight coil from the stator assembly, and installed yet another grey light coil, just in case the first three I tried were bad. Then I rewired the wiring block to factory, put everything back together, and SAME SHIT!

So I grab my new multi meter, and start checking. All voltages checked at a fast idle.

Voltage at taillight socket with headlight on, no taillight bulb: 13 VAC.

Voltage at taillight socket with headlight off, no taillight bulb: 9 VAC

Voltage at wiring block with headlight on, no taillight bulb: 13 VAC

Voltage at wiring block with headlight on, bulb installed: 0.3 VAC

Voltage at wiring block with headlight off, no taillight bulb: 9 VAC

Voltage at wiring block with headlight off, bulb installed: 0.3 VAC

What's going on here? Why do I lose all taillight power when there's a bulb installed? I've tried several different 5 watt bulbs. Somebody must have a clue what's going on. Could it be a bad switch causing the issue? I don't know what else to try.

Re: 78 Maxi Tail Light Gremlin

iv seen wires give the voltage reading and suddenly drop when a load is applied. what happens is the stranded wire is not so much stranded but barely hanging on by one tiny strand(shows up on meter) and being compromised it wont carry the load.. .

Re: 78 Maxi Tail Light Gremlin

I get what you're saying, pat. But if I apply a different power source to the same taillight wires, it lights. But I have nothing directly out of the stator, if a bulb is installed.

Re: 78 Maxi Tail Light Gremlin

Do you have another flywheel you could try?

Re: 78 Maxi Tail Light Gremlin

Yeah Mike. I've got two or three laying around. Ya think that could be it? I'll try anything.

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