Topic: Wiring in 2nd headlight

[51plymouth]

Just got done attaching the sidecar to the bike, a 1978 CB750k, and I've moved on to the wiring of it.  Everything is wired, all running/tails/turns work, but the headlight just wants to pop fuses.  I'm sure it's just too much current draw, so I've disconnected the headlight on the hack, but I'd really like to have it wired in and working since I do a LOT of riding on deer-infested country two-lanes.  Any help is MUCH appreciated.
And here's your pic...it looks like the light is on, but it's just the sun catching it just right.


Thanks
Jack

[Jerry Rxman Griffin aka MuthaF'er]

Nice bike and nice setup.

Are you aware that these bikes have a marginal at best charging system?! I'd be real surprised if the system could keep up with 2 headlights. Mine has a hard time keeping up with a halogen headlight and 3ohm coils. Works fine on the road but not around town unless I keep the rpms up as the charging system doesn't even put out until 1800rpm or so. I can not seem to get the output above 13V and they are designed to have 14.5V output at mid rpm range. I keep a Battery Tender installed so the battery is at full charge in the garage and when I'm ready to hit the road.

A couple thoughts. Some of the guys are wiring in relays but I'm not sure what/why. Do a search on that. Does your K have a 3 slot fuse box or a 5 slot fuse box? My F uses the 5 slot with 2 only used as spare fuse holders. You could wire in one of these spare slots for the 2nd headlight as you WILL have too much draw using a single 7A fused slot. Some of the guys are switching to aftermarket auto type blade fuse boxes too.

Before you get too deep into this you should check the charging system output voltage vs the charging chart. I'd check your stock setup first. If it will maintain the 14.5V output with one headlight I would "hotwire" the 2nd headlight through a 2nd circuit and check your output. I'd also consider the wiring harness wire gauge and watch for over heating/melting.

Be careful with this. I'd be surprised if the 77/78 K's have new harnesses available. The charging systems are perhaps the weakest point on these bikes. If successful please let us know what you did.









       

[traveler]

It is this exact issue with the charging system, that made me set up my lights on a separate switch, and left off....to be used only in case of emergency.  Easier on the whole electical system to leave them off unless it's dark.  The only lighting that is on all the time is the tailight.

I'd recommend more do this as well.  Yes, it makes you less visible, but it saves the charging system.

~Joe

[Gordon]

I think with bikes this old the ability of the charging system is different from bike to bike.  My K1 could probably handle an extra headlight just fine, but I know my 550 couldn't.  

If you've determined it can handle the extra draw, my suggestion would be to run it on a separate switch wired directly to the battery with an in-line fuse.  That way you have independent control of the extra light and it won't be taxing the ability of the contacts in the starter and dimmer switch.  


edit:  Traveler beat me to it.

[traveler]

Even the new Harley Road kings have a toggle to turn on the smaller headlights on both sides of the main one.

When I wired my racer, I wired it so I can ride with no light on except the tailight.  Since, I ride 99% of the time on my racer during the day, my battery stays nice and charged.  The one time it started getting dark, I simply flipped a toggle switch to turn the lights on....gauge lights and headlight came on, and then flipped my other toggle between high beam and low beam.

I love simple wiring diagrams!

P.S.  I agree, if running straight from the battery to the toggle switch, an in-line fuse is a smart move.

Good luck!

~Joe

[nokrome]

check out these guys http://oregonmotorcycleparts.com/ their regulator charges at 14.5 at idle, i also run their single unit reg/rec on my project bike, it wont make your output any higher but your battery will always be charged


  p.s. welcome, that is a super sweet set up

[andy750]

+1 very nice sidecar setup! Where are you located?

Welcome!

[51plymouth]

First, thanks for the props everybody, the bike itself came to me in great shape in a horse trade, garage queen, about 24k on the clock.  I've got the carbs off of it as we speak, as it was painfully lean.  The sidecar, however, is a totally different story.  Basket case, missing parts, the parts that were there were rusty, horrible paint, dry-rotted carpet & seat, mouse-chewed wiring (what was left of it), broken lenses, etc...I spent last winter while I was snowed in restoring it.  Bike is a 1978 750k, sidecar is a 1972 EZ-Rider--they seem pretty rare as even most sidecar guys haven't heard of them.  Located in York, PA. 
As for the headlight ideas, I guess I'll just be losing the light and plugging the hole.  I like the look of the sidecar light but since the bike is so unmolested I hesitate to do anything that might screw up what's there.  As of right now it charges and runs what seems like enough current, but I don't like the "direct wire" approach, as the light is a hi-low and I don't want to hit two switches to change both lights, so I think I'll wait until the electrical needs some lovin' and I'll go with the new fuse box, heavy wire, relays, LED low-draw bulbs, etc...
Thanks for all the help,
Jack

[Mdub]

One of these:
http://www.ddmtuning.com/Products/DDM-HID-Kit-Slim-Ballast-35W-or-55W
$40 with a lifetime warranty.
You'll neeed a couple H4 reflector housings.
Choosing the 35 watt X 2 = ~5.5amps total and 2.75 amps each.
I would wire the side car with it's own switch so you can turn it off in the city.
Coupled with the reg/rect that nokrome recommended at:
http://oregonmotorcycleparts.com/Reg_rec_units.html
(also with a lifetime warranty) and you'lll have more than enough light and power.
That'd be bad@ss, you could just fry the little sucker's retinas!
Good job on the side hack and good luck!
Mike

[TwoTired]

Do you know the wattage of the headlight you are adding?  Is the motorcycle's headlight stock?

The main fuse is 15 amps and normally 10-11 amps run through it.

A headlight draws 4-6 amps-ish, but that really depends on the wattage selected.
Small wonder you are blowing fuses with the added load, depending on just where you tapped into the bikes power (probably should have told us that).
I expect the sidecar tail light is powered, too.  So, there are more bulbs that are drawing power than just the extra headlight.

You will either have to increase the size/rating of the main fuse.  Or, add another fused circuit for the sidecar's power consumption.  The later is probably a better solution, as hot fuses can melt the fuse block plastic.

I don't see how the oregon regulator can't make the alternator produce more power.  Defies reason, as it cannot give the alternator any more voltage than the stock one can (assuming the stock one is in proper working order).

The stock 750 Alternator makes about 210 Watts at 5K RPM.  Much less than peak power at idle.   The bike alone uses 120-130 watts with the key switch on.  So, it is best to know just how many watts you wish to add to the bike's electrical load.  If it is more than the alternator makes, the battery depletes.

Cheers,

[dave500]

i have a volt meter,and switch on and off my head light as i see fit,when the volts get near 15 on goes high beam,manual regulated.i dont do much traffic riding,but when i do the voltage soon goes below 12!these have a feeble alternator.

[TwoTired]

i have a volt meter,and switch on and off my head light as i see fit,when the volts get near 15 on goes high beam,manual regulated.i dont do much traffic riding,but when i do the voltage soon goes below 12!these have a feeble alternator.

If you are measuring battery voltage at 15, your Vreg isn't dong the job intended.  It's purpose for being is to keep the battery from getting above 14.5V.
If yousr is doing anything functionally, it is at least adjusted improperly.

Please understand:
1 - The output of the alternator is variable with RPM.  Higher generally better but is is not a linear relationship.
2 - The Vreg can give full battery voltage (whatever is there) to the alternator for max power at whatever RPM the alternator is spinning.  Or, it can reduce the voltage passed to the alternator to reduce its output.

That's it.  The Vreg moniker is applicable indirectly as it is the battery that determines bike system voltage.  The Vreg and alternator just try to keep the battery voltage consistent.

The system load doesn't care where the power comes from.  Kinda like welfare recipients.   

FYI, if the voltage passed to alternator from regulator is feeble, so will the alternator output.

Cheers,

[Jerry Rxman Griffin aka MuthaF'er]

Then there's always the 750A field coil rated at 290W if you need the extra output to go along with the 2nd fuse block.

[nokrome]

Then there's always the 750A field coil rated at 290W if you need the extra output to go along with the 2nd fuse block.

 is there a way to tell the difference between the 750a field coil and a regular one if they are not in the bike?
    is it a bolt in replacement?

[Jerry Rxman Griffin aka MuthaF'er]

Just a little complicated and I don't know anyone that has actually done this. I hope to but that will be part of the build. The windings in the 750A are larger wire/smaller gauge with less resistance. This is th only apparent difference in the charging hardware. If I remember correctly the 750A is 4.2ohms vs 7.something for the 750K/F. The ID numbers are different on the side of the coil. I am away from home until this evening so I do not have access to both numbers. I'll try to remember to check back in this evening. Same physical unit but wound with different wire so it's bolt in. The 750A uses a different rectifier that is solid state presumably to handle the extra POTENTIAL load. POTENTIAL if you don't use the load. It has 2 reds (hot) and 2 greens (ground) presumably for the higher output. Without having both in my hands right now I'm going to assume the connectors are different too but there should be no reason this can't be overcome. The extra red and green make me a little leary of using our stock K/F rectifier for fear of overloading it but they are easily and cheaply replaced. I have an Electrosport _ _240 R/R unit and they tell me it will handle all the loads we can put on it. My only hesitation using my bike as the guinea pig during my restoration is that I found a NOS wiring harness that I plan on using and I do not want to melt it which is always a potential issue. I have seen only 1 other NOS harness available in 4 years. In (my) theory this should work just as it works on the A.