Crazy thought - running two batteries


XS400 Enthusiast
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So in my quest to better understand the electrical components of the motorcycle electrical systems, I've tried to simplify things by seperating them into two categories....
Keep in mind I am not an electrician and have zero prior experience working on anything electrically related.
Please correct me if any of this is wrong!!!

Category One - this contains things that run off a fully charged battery, and therefor require the strongest voltage, such as the starter. This is the part of the system that requires a voltage regulator, a charging system, and is constantly working, unless the bike is off. It is either discharging power, or charging the battery.

Category Two - everything else that requires power, when a circuit is closed - ie: signal lights, brake lights, etc. This part of the system could potentially run without the voltage regulator, but if done so, would eventually drain the battery.

My bike, in it's current state, is an electrical gongshow. It has been modified, fixed, patched, redone, scrapped, multiple times. It is a blend of aftermarket pieces, stock pieces, and patches/fixes/zip ties/tape/shoddy soldering.

I am wondering if I can do the following:

Modify the electrical system to run off of two batteries.
The first battery would manage the voltage regulator, the starter, and hopefully the headlight.

The second system, would then run all the other pieces - such as the signal lights, horn, and act as a backup onboard battery for starting (by switching the wires over from battery one to battery two).. The benefit of this, is that I could easily bypass all the complicated systems and simply hookup a new set of signal light switches to the 2nd battery, that would need charging periodically (once per week perhaps?)

Is this as dumb and stupid as I think it is? Or could this possibly work? I have an 83 Maxim and I just am not confident reading the complicated wiring diagrams... I wish I understood this stuff better because I would like to have really neat and tidy wiring that works properly but at this point I feel like if I hit a bump the entire harness is going to fly off the bike and wrap around my neck and kill me.

Anyone out there who could simplify things for me would be greatly appreciated...
Your basic ideas are not correct.
The charging system, the regulator, rectifier, field coil and stator and the wiring to hook it all together just charge the battery. That's it.
Everything else runs off the battery. The starter does draw the most amps. Thus is only for a short time.
The field coil for the charging system and the coils for the ignition are a constant draw. They draw power anytime the key is on.
The headlight and the turn signals are about tied for draw.
The rest of the stuff goes down from there.
The two battery idea isn't really very good. If your charging system can't keep one battery charged, it can't charge two.
I would suggest you go through your electrical systems and fix everything. Start at one end of the bike, working to the other. Clean and tighten every connection you find. This includes all the switches, most can be taken apart to clean.
Your repair manual should have a wiring diagram for your bike. Trace each circuit on the bike with the diagram. This will help you understand much better how things work.
If you have any problem, using the diagram to trace the wires and checking for voltages all along the circuit from the battery to ground will tell you where the problem is. Be sure all the places ground wires touch the frame or engine are all clean bare metal to clean bare metal.
As you go along the circuit you will have voltage near battery voltage. If at some point along the circuit you find low or no voltage the problem is between where you find the low/no voltage and the last place you had good voltage.
Thank you for the detailed reply Leo! @XSLeo

I realized over the weekend my summary above was nonsense. I was able to dive into the bike a bit more, and as you mentioned, I have a much better understanding of it now. I took apart the left hand controls and cleaned the entire unit. I then realized that this bike does not have a horn. I hadn't even tried it yet. So, I took a spare horn that I had, and wired it up, then found the two exposed leads for the horn (pos and neg) and then hooked it up, and it worked. I'm going to make the entire electrical system a big project, I enjoy that kind of thing, and it would be good to know how and where each part functions.
One thing that I'm considering is running inline fuzes rather than a fuze box. My reason for this, is that it will allow me to run less wire, as opposed to running a lead all the way back to the seat (or first thru the seat) to accept a fuze. I realize I may be saving minimal (if any) wire length, but doing the project this way will allow me to isolate individual lines rather than running a fuze box style fuses, and I can replace it in pieces as opposed to all the wiring at once.
Really the only electrical problem on the bike right now is that the headlight only has one setting (LO - works, HI - no power to light) and then the neutral light indicator on the speedo does not light up when the bike is in neutral. My understanding of that one is that it could be multiple things:
-a loss of ground from that instrument panel (although the other high beam indicator works, even though the actual high beam itself doesn't work)
-wired incorrectly (stock wiring harness into LED instrument panel)
-missing ground somewhere
-neutral indicater switch itself is malfunctioning.

What piece of the electrical project would you suggest replacing/repairing first? I'm pretty green to this bike thing but I'm eager to learn and start working on it more as the temps dip down. I fixed my oil leak and I'm pretty stoked about that.
The headlight, if low beam works but no high beam, it's probably a blown bulb. You can pull the bulb and check to see if blown by jumping from the battery. Check the wire colors on the plug to the headlight. Black wire is ground, yellow is high beam green is low beam. Just jump the same way.
On the stock neutral light power goes to the bulb, from the bulb down to the neutral light switch, when in neutral the switch grounds the circuit.
On the LED indicator, most LED lights are polarity sensitive. Power only flows one way. The wires for the indicator may be backwards. Before I looked at that I would unhook the wire from the neutral switch and ground it. If the indicator lights then the switch is bad. If no light then check the wiring.
On the fuses replacing the stock glass fuse box to blade type fuses is a good idea. I have done this several times to fix crappy fuses. Inline fuse holders work well. I would just cut out the stock fuse box one set of wires at a time, Add the new fuse holder in, then go to next fuse. Having all the fuses under the seat is the easiest way to do this. Especially if your harness is all stock. Handy to have all the fuses in one place.
On my 75 XS650 I built my own harness. I ran one inline fuse, 20 amp to the main switch. From the main switch to a 6 fuse block that uses blade fuses. I then ran from one fuse to each circuit. ignition is one 7.5 amp fuse. Headlight is one 10 amp fuse. power to alternator is one 10 amp fuse. Turns and brake lights is one 10 amp fuse. Horn on one 15 amp fuse. The double horns draw a lot of juice. The last 10 amp fuse feeds power to the ignition on/off switch and starter relay. The ignition I have powered through a relay triggered by the ignition on/off switch.
Damn Leo thank you! All great advice. I'm 100% following what you're saying about the fuses, thanks for making that so clear.
That electrical stuff is my biggest concern. After that, most stuff is good except I would consider setting the valve clearance and then doing general preventative maintenance ie chain etc. The rest is cosmetic, which to me is the fun stuff.
Thanks again for all those great tips! I'm thinking I could even use the existing fuse box now, and just convert it to use the blade fuses instead of those shit glasses fuses that get knocked out and around. Man I hate those things.
Remember the dohc xs400 has a brush type charging system like the xs650 has. Those can and do go bad.
One thing I have found is if you start at one end of the bike and work to the other end, inspecting every connection in the wiring. Cleaning and tightening with a tiny dab of dielectric grease to prevent corrosion will often fix things that can be troublesome.
When you first get a bike going through the basics of a tune up will help you understand things better.
Start with the Mechanical things first.
Cam chain adjustment
Valve adjustment
Ignition, If points then set gap and timing. If electronic just check timing.
Do these things n this order and you won't have to backtrack to redo things.
Once you get these done and it still has running issues, then you can dig deeper to determine if the issue is ignition or fuel related.