Solex Lighting

Hello All,

I have a Solex 3800 which didn't have an engine cover/headlight, etc. I recently purchased some of the parts from Velocruz, but I'm having a hard time putting them together.

I know there's a lighting coil and it appears that connections are made via a left-hand thread (wood screw lookin' thing)?

Also, it appears that the switch makes contact with that screw (lead) as well.

One wire on the headlamp assembly attached to the switch lead. Is there another wire I'm missing? maybe to ground.

I'm lost. Any help would be much appreciated.

Re: Solex Lighting


Yes, you need a ground. On my bike, the ground is picked up on one of the 4 bolts that holds the fuel pump in place. Use a crimp/solder ring terminal to pick up a ground there.

On the rear of the engine cover is a little tab, that looks like a spade terminal (it's part of one of the switch contacts). That is the point where you hook up a wire to the tail light. The tail light should use the fender as its ground.

Re: Solex Lighting

Thanks legendre,

but where does the ground attach to the headlight? I do see what looks kinda like a spade terminal (copper colored) but it didn't come with a wire. Is that where it goes?

Thanks for your help, once again.

Re: Solex Lighting

Got it! Thanks again for your help. That little thing doesn't give off much light though, does it?

Re: Solex Lighting

Nope, not really. Check the bulb - what is it, like 12W?

Glad you figured it out.

Re: Solex Lighting

John, Are you using the bulb from Velocruz? If so, your 1973 coil and flywheel aren't powerful enough to light up that 6V 15W bulb. The original bulb for the 1973 electrics was only 6V 6W.


Re: Solex Lighting

Hi Brian (& Legendre),

Yeah, I'm using the 15W bulb. Sounds like I need the 6W, huh?

Re: Solex Lighting

Yeah, don't stress the lighting coil.. get a correct bulb.

Re: Solex Lighting

Yes, but the original bulb is a screw base bulb and will not fit in the lens that you have. You may be able to find that 15W style bulb in a 6W size, but I don't know. You may be able to find a socket adapter to be able to use the original screw base style bulb in your Velocruz lens. see attachment. The only place that I know of to get these adapters is from <>

in France, but I'm sure they must be available somewhere over here.

Rear bulb should be 14V AR, but you can use a 12V 6W .5A or a 12V 4W .35A bulb. The only place I know of to get the correct 14V AR bulb is lesolex.

You can e-mail Jeff at Velocruz and see if he has any of the bulb adapters or 14V AR bulbs.


Re: Solex Lighting

Thanks Brian,

I emailed Jeff about a bulb, and he said to send it back and he would send me the correct one.

Just curious, could that year Solex be updated with the more powerful flywheel/coil combination? Doubt it would be worth the cost, but I am curious.

Re: Solex Lighting

Yes, you can install a Hungarian flywheel and lighting coil if you wanted to. The parts are interchangeable. The Hungarian coil has an extra lead that can be used for a brake light system.

Or, if you have a flywheel from a 1975-78 4600 V2 or V3, you can put that on your old 3800 and it would light up that Velocruz 15W bulb. I have one 1973 3800 set up like that. (See attachment) I rebuilt this bike using mostly Velocruz parts.

I'm guessing that Jeff is going to send you a screw base (flashlight type) bulb that will not screw into the lens sold by Velocruz. You might want to double-check with him about exactly what he is sending. You may need an adapter.



Re: Solex Lighting

I'm going to check with Jeff on that. Are those 'knobby' tires on your Solex?

Re: Solex Lighting

No; no knobby tires on my bikes...just a grainy photo. It's very important to use only tires with the straight tread vee's, slants, zees or anything irregular. If you don't use the correct straight tread, the roller will wear away and you will get a lot of vibration.


Re: Solex Lighting

Hey BrianSolex,

I just picked up two more Solexes. I was wondering if you could tell me their age. I'm not sure if you need the motor serial or not, but the bike vins are:

Horse: 8087359

3800: 8020192

I hope to be able to put at least one bike together. Are any of the parts interchangable?

Thanks for all your help.

Re: Solex Lighting

Congratulations! Addicting, aren't they?

The second one, frame number 8020192, should be a black S 3800. It is from 1973, a little earlier in the year than your other 1973 S 3800. It should be exactly like your other S 3800, with the exception of possibly the brake levers. They will both have the reverse levers, but the earlier bike's levers might be a little more rounded off on the bottoms...maybe. The later one's levers might be a little more squared off on the bottom. They were changed right around those serial numbers. The motor serial number will probably start with a 528 or 529. Let me guess for far off am I?

The first one, frame number 8087359, is a model 4600 V2 from 1975, approximately April. It should be yellow, orange, blue or black. I'd like to guess the motor serial number of this one also, if you'd help me out....7217105. How far off am I?

Both of these bikes were made at the SINFAC factory in France and were intended to be sold in the US. In other words, they were not sold in France and then imported here. The basic frame and motor parts are the same. They both use the cyclomoteur 3800, but the cylinders and cylinder-heads are different between the two. The older one should have the TUM 80A cylinder and the 4600 should have the TUM 80A CM 6.5 which is a better cylinder. The main differences between the two are the handlebars, controls and lighting, which all must be changed as assemblies if you are going to mix-and-match. For example: if you use the 1973 3800's motor on the 4600, it will not light up the lights and there is no coil for the brake lights. You would need to put the 4600's flywheel and coils on the 3800's motor. Another example: you can not put the 4600's controls on the 3800...the handlebar diameters are different. Another example: if you put the 3800's headlight/hood on the 4600 motor, there is no power supply stud coming out the back of the stator for the switch to contact. There are many examples like these.


Re: Solex Lighting


yes they are addicting. I've got an envious friend that wants one so I'm going to try to put one of the two together for him. They appear to have good compression, so I've got my fingers crossed.

You were real close on the serial numbers. The 3800 motors is 5281184 and the 4600s is 7214778.

As for the handlebars, I haven't looked at them closely to see a difference. The 3800's paint and chrome are in amazing shape considering the year. I will try to post some pics when I get a chance.

Thanks again.

Re: Solex Lighting

Thanks for getting back to me with the serial numbers! I like playing that guess the Solex serial number game.

The 3800's handlebars are about 23 mm, and the handlebars on the 4600 V2 and V3 are about 22 mm.

I'm looking forward to seeing photos of your stable.

What color is the 4600? I'll guess yellow.

Solexly, BrianSolex


Re: Solex Lighting

amazing, where do you get this stuff?

no problem getting back to you with that, I find it pretty interesting.

Kind of ironic... the 3800 has a service sticker on the rack from an old gas staion I grew up near. Joseph's (otherwise known as Mo's) Service Station ( a Mobil I think). It hasn't been around for at least 20 years, however, I recall he used to be a dealer for either Indian or Whizzer, I forgot which.

To top it off, when I called the guys on his ad in the paper today, it turned out that I had to drive about five blocks from where I work downtown Detroit. It was a very good day!

BTW the 4600 is orange.

Re: Solex Lighting

Thanks John!

Here's a photo of an orange 4600 V2.

Best of luck with your bikes. If you have any questions or need any help, just ask.


Re: Solex Lighting

Hi John, Did I read on another post that you got both Solex's for $100? If so thats a pretty sweet deal. Also was it you that was bidding on the 3800 in Grand Rapids? That one went for over $500 and I don't even think it was running.

Re: Solex Lighting

Hi Dan,

Yeah, that was me that bought the two for $100. I actually got one of them running last night although it still needs work as it only runs well with the choke on all the way. I did bid on the one in Grand Rapids as well, however, after finding the two in the paper, I know longer wanted to drive an hour and a half to get it. I wouldn't have bid that high anyway, so everything worked out well.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account