Headlight Voltage Drops

A good, but non-XS example of less than optimal OEM Yamaha wiring, is the white plastic 3-pin connector block for the 3-phase AC wires from the alternator on the 73-75 RD350. These had a bad tendency to get hot, melt and sometimes short out the stator. This was a very common occurrence on those models.
This just illustrates my point, that original is not always the best solution. And is why I strongly recommend relays for the headlight and coils in the XS.
 
A good, but non-XS example of less than optimal OEM Yamaha wiring, is the white plastic 3-pin connector block for the 3-phase AC wires from the alternator on the 73-75 RD350. These had a bad tendency to get hot, melt and sometimes short out the stator. This was a very common occurrence on those models.
This just illustrates my point, that original is not always the best solution. And is why I strongly recommend relays for the headlight and coils in the XS.
My XS650:
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Once upon a time, I put dielectric grease on there. That was the probable cause. It's all fixed now, pins and all. Yes, there are better quality connectors available.
 
I fixed that on another bike, by installing a couple of relays. One for low and one for high beam. The original supply to the bulb was used for controlling the relays. The relays are supplied directly from the battery, via a 10 A fuse, using 1.5 mm2 wire. This bypasses a lot of potential voltage drop issues.
I use relays on all of my vintage cars. It's a cheap fix and helps lengthen the life of hard-to-replace original switches. I also run them on my cop bike. I should probably do the same to the XS but I am thinking of changing the whole headlight out.
 
My XS650:
View attachment 233649View attachment 233650

Once upon a time, I put dielectric grease on there. That was the probable cause. It's all fixed now, pins and all. Yes, there are better quality connectors available.
That block is at least better at handling large currents than the RD one, which had pins/ sockets maybe one third the size of yours. And about as weatherproof....
 
I'm not a DC electrician. One thing I have experienced, un like ac, the more copper the more electric gets threw. If u have bs jumper cables that don't do the job on a cold day. 2 sets would or when bumpers where metal you could touch bumpers and put both on positive. I wish the harnes used a gauge bigger wire.
Not trying to hijack the thread but I wish my almost 100% stock system was a little better. Mostly to send more juice to starter. Can someone explain the relays? Is it easy to change them to in front of draw instead of at it or after?
 
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I had a big voltage drop on my new to me '77. Cleaning the Ignition Switch contacts was a big help. I was losing more than a volt across the key switch before cleaning the internal contacts. Your nice schematic with measurement values suggest you are losing ~1v through the switch. That right there may be the problem. Some of us use cheap digital volt meters to monitor our system. These run $9- $12 online.
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This is my installation using velcro tape. I have this connected to Brown (system 12 volts after the key switch) in the headlight shell. It registers 11.7-11.8 volts (11.6v in the picture when it hasn't been run in10 weeks, time for a charge) with engine not running and registers 13.9-14.0 volts while the engine is running more than ~2300 rpm.
 
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I'm not a DC electrician. One thing I have experienced, un like ac, the more copper the more electric gets threw. If u have bs jumper cables that don't do the job on a cold day. 2 sets would or when bumpers where metal you could touch bumpers and put both on positive. I wish the harnes used a gauge bigger wire.
Not trying to hijack the thread but I wish my almost 100% stock system was a little better. Mostly to send more juice to starter. Can someone explain the relays? Is it easy to change them to in front of draw instead of at it or after?
Joe, I mounted the relay for +12VDC to the coils, just next to the coils. That way, the original (brown) supply wire could easily be connected to the control terminal of the relay. And the only extra wiring of any length is from battery to relay.
As for your wish for more juice to the starter, a new starter solenoid (which is just a very high capacity relay), and new, possibly slightly heavier gauge cables is about all you can do, apart from a battery with a higher CCA rating.
For headlight relays, I would try to mount them inside the headlight, or as close as possible. For the same reason as my coil relay, and also the advantage of running only one shared power wire from the battery. (Instead of separate hi and low beam wires) But that is something each should decide on, as circumstances may vary.
 
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Some of us use cheap digital volt meters to monitor our system.
I would love to have an ammeter with a needle. One that actually works, rather than the never functioning Lucas meters.

registers 13.9-14.0 volts while the engine is running
Yes, it works. I still like the ammeter.
 
I had a big voltage drop on my new to me '77. Cleaning the Ignition Switch contacts was a big help. I was losing more than a volt across the key switch before cleaning the internal contacts. Your nice schematic with measurement values suggest you are losing ~1v through the switch. That right there may be the problem. Some of us use cheap digital volt meters to monitor our system. These run $9- $12 online.View attachment 233659 This is my installation using velcro tape. I have this connected to Brown (system 12 volts after the key switch) in the headlight shell. It registers 11.7-11.8 volts (11.6v in the picture when it hasn't been run in10 weeks, time for a charge) with engine not running and registers 13.9-14.0 volts while the engine is running more than ~2300 rpm.
I should have added that 14.0 volts at the headlight shell (meter) equates to ~14.4 volts on the battery terminals. That shows the ~0.4 volt drop across the ignition switch.
 
I should have added that 14.0 volts at the headlight shell (meter) equates to ~14.4 volts on the battery terminals. That shows the ~0.4 volt drop across the ignition switch.
That is actually a bit weird, unless what you describe is with a running engine and headlight on (i.e the ignition and headlight drawing around 6-7 amps through the ignition switch)
 
I should have added that 14.0 volts at the headlight shell (meter) equates to ~14.4 volts on the battery terminals. That shows the ~0.4 volt drop across the ignition switch.
You have the meter connected to brown wire out of switch? So it's reading after main fuse and key switch, but before fusebox and ignition👍
 
Can someone explain the relays? Is it easy to change them to in front of draw instead of at it or after?
In the simplest of terms; they use a low amp circuit to switch (connect) a high amp circuit. The goal is to eliminate losses through the switch and reduce damage to the switch from heat, arcing, etc. Typically installed ahead of load (draw) at a most desirable spot.

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There are different kinds of relays, but the above pic shows one and the terminal numbers are standard: The switching circuit - power or ground - connect to 85 and 86, the target power supply goes in @30 and the load is connected at 87 (Normally Open) or 87A (Normally Closed)
 
Just thinking out loud here not read through it all.
Where to insert the relay and what other wires to replace.
The idea is attractive but what if the problem is somewhere else in the circuit.

Looking at an 78 Schematic it is a lot of wiring that is involved .
Thinking out loud again .. If the partial ground is there and a relay is used.
Headlamp is on fine.
Is it not a risk that the partial ground is left and are demanding more alternator up time.
Going hot and fry the rotor.
An alternator that can already have problems deliver to the demand.

The owner here appears to have electrical competence and can be able to find the fault
I almost never do it but measuring current after fuses and so is an option.
As well as resistance to ground from special points of interest.
 
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The above is for an older XS (w/o light checker, reserve lighting) R/Y is headlight circuit from fusebox
 
Yep, the 78 wiring diagram sucks, best way to trace out the connections would be to print it on a large piece of paper and go over it with a highlighter. One of the satellite payload engineers I used to work with would do that to trace out switching paths in one of the more complicated satellites we worked with.The other problem with the diagram I have is the wires go to black boxes with no indication of what goes on inside the box... a big PITA to work with.

Anyway I realized I forgot something in my drawing, the circuit also loops through the reserve lighting unit so there is even more wire length and connectors. So far by cleaning and tightening connectors I gained 0.5 volts or so, going to try some more before I give up on that.

Also, as gggGary mentioned the stock headlight is 50 watts on high beam, for some reason I had it in my mind it was 55. I did try connecting a stock headlight and gained about 1 volt, still no good but better.

Really want to see that 60 watt halogen running where it should, I have the Silverstars in the high beams of my Forester and they are nice and bright.
 
You have the meter connected to brown wire out of switch? So it's reading after main fuse and key switch, but before fusebox and ignition👍
I am monitoring the brown (+12v, '77) after the iggy switch. Members here suggested that ~0.5v drop across the switch is normal. After I cleaned my switch I measured a substantial increase in "system volts". Search "New to me XS 650". I do not remember the sequence of my discoveries aided by so many members here.
 
When I built my Bobber I removed the e-start and ran a much smaller battery with just enough juice to fire the points for a kickstart. The problem was if the headlight was left on during a start it basically killed the battery. Because the horn draws so much I installed two relays in the bucket. One for the horn and one for the HL. Horn button powered the relay and took the load off the switch and the light wouldn’t come on until the bike was started.
 
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