Electrical help needed please !

[Strebe]

I think that the problem is caused by the resistance of the switch. The solution is to add a relay in a new circuit that feeds the headlight directly. It’s something I’ve been meaning to do for ages. I bought a couple of relays for the purpose from a guy in the US.
But suitable relays are readily available over here, and if you Google “adding a headlight relay” you’ll find some suitable wiring examples.
But I’m sure that lots of members must already have done this on their own bikes - or am I wrong?

[Strebe]

http://www.jeepfan.com/projects/brighte ... ht-relays/
For example!

[Strebe]

Here’s a better, motorcycle specific example:


https://www.motorcycleclassics.com/mc-h ... lamp-relay

[johny brando]

if the ballast resistor is still in circuit disconnect it & join the two blue wires together that come out of the main harness

AAAAah will do & I'll be sure to let you know . Cheers Lee

UPDATE !!!!!!!! z1bman, Keith, Paul & others . Having now checked "if" the Ballast Resistor is there ..... & i can confirm now " NO it was gown-removed " & it appears I must have just tried to re-connect the wiring connections linking the switch blocks to the 2 Ballast resistor connectors that were then left there...this with limited zero success- but thinking it all was OK, as every thing appeared to work alright ....so I suspect it's been like this for 37 years now ! Ooops.
Righto overview - I don't have a decent wiring diagram , just whats in the Clymer manual & that don't even show or mention the B-Resistor or the wiring colours !!! Mmmm . It's a late 1975 900 A4 . So just to confirm R/H switch block = 4 pin multi plug & 2 seperate Blue wires ..one has a double female bullet connector & the other a Single male bullet connecter.
L/H switch block = 6 pin multi plug & 1 Black wire with male spade & 1 Dark Blue wire with male bullet. ( the switch blocks are both in good nick as a couple of years ago I completely went through them...stripped ,cleaned & lubed them both & they work fine & still are 100% ) Next to the coils position on the frame, the main wiring harness there has the 2 wires exiting 1 = Blue/ White tracer & male bullet and 2 = plain Blue with female a bullet connector .
So taking note & gratefully following the sound advise from above... I joined the 2 wires exiting the harness there together . I then using the existing bullet connectors linked the other 3 blue wires from the switch blocks together & Mmmmm this now a different wiring configuration to what I had .... but it again all appears looks right now . Right..so I get the meter out again & I now have got 11.5 v at the Main bulb connector on both Dip & Main pins ( this is with the plug not attached to the bulb ) ....... & when it's attached = BETTER than before as now it's 10.2 v when connected & before it was only about 8.5 v . Well, thats great & I'm chuffed THANKYOU but..... I'm still not sure it's 100% right because of that voltage drop I'm getting when the connector is attached to the bulb ????
I then thought I should also follow Paul's sound prior guidance too ....this assuming he meant that the bulb /spade - Wiring configuration was likely wrong, with this then causing the issue ( very valid point too ! ) so, I tried every which way wiring combination to the bulb/spade connection points & the only one way that it all worked properly was the way it was already connected... & I also visually checked that only one filiment was powered & active at any time . Mmmm so now with my very limited knowledge !!! I think that perhaps that side of it can be dismissed although it had very real & probable possibilities ! & thanks Paul... that was good call mate.
I don't really know where to go from here as 10.2 volts at the bulb ....well is that correct ??? I've no idea ! Any one out there with a Halogen H4 bulb fitted that they can put a meter on & relay to me what voltage they have on the terminal point with the connector plug powered (i.e. drawing current ) but...disconnected from the bulb spades ...... and then what voltage they have with it connected to the bulb itself ???????
Thanks for the help guys ...........Lord knows I need it when it's electrical related ! Over N Out.

[KeithZ1R]

You clearly have loads of patience my good man well played for perseverance and you clearly have more idea than you think, there will always be a voltage drop across the bulb when its on and this figure will be dependant on the overall wattage of the bulb.
Keep up the learning because despite how it looks the wiring on these old dinosaurs is relatively simple once you have a good idea of the basics

[ZedHead]

The bulb is effectively internally wired in series with the central position intended to be earth. If for some reason wires are crossed and the earth moved to an end position then both filaments could be operating in series. If, as you indicate the voltages are correct at relative bulb terminals it should be ok. Plus it should be easy to check as both filaments would be lit simultaneously, although dimly, and the dim switch would not operate as you would expect.

I would start by checking voltages further back with the bulb in situ, the dim switch being a good half way point to start.

Headlight.jpg (96.05 KiB) Viewed 4672 times

[Strebe]

Top marks for perseverance!
It’s quite a while since I’ve had to use Ohm’s law in anger, but if we look at the voltages you’re seeing, and the nominal Wattage of the bulb:
60 Watt nominal rating at 12Volts implies a current of 5 amps. But this rating assumes 12Volts across the bulb. With a lower voltage, the bulb will be running cooler ( which us why it’s dimmer) and have a lower resistance. But if we assume a 5 Amp current, and a 1.4 Volt drop in the circuit to the bulb, were only looking at a resistance of 0.28 Ohms! That’s a pretty low resistance. Some of it obviously comes the wiring, but most will come from the resistance of the various switch contacts. Most of that resistance can be eliminated by using a relay.
As the motorcycle classics article says, a 9006 halogen bulb (55 Watts) rated at 1000 lumens at 12.8 volts gives only 510 lumens at 10.5 volts - a 49% drop in output for an 18% drop in voltage.
I remembered that the relays I bought were the matchbox relays mentioned in that article. I was very impressed by the customer service of the guy at culayer.com, $40 seemed damn good value.

[ZedHead]

I am a little confused by talk of voltage drop across the bulb. This is of course correct but it should be the full 12 volt operating voltage, supply to earth, and nothing to do with the 1.8v drop that you are seeing at the connector before the bulb. You need to trace this back to through the circuit including before and after the switches until you find 12v and the source of the 1.8v drop. Connector and switch contacts are always prone to oxidisation and are prime suspects.

[Strebe]

The bulb is just one resistive element in a simple circuit. The current is constant throughout the circuit. The circuit includes the resistance of the wires, of course, but also that of the switches in the circuit. The switches are likely to be the biggest contributor, besides the bulb, to the resistance of the circuit. The fact that, under load, there is only about 10 volts across the bulb is the result of the extra resistance in the circuit - as we know, V = IR, if we lose 1.4 Volts across a resistor in a circuit carrying 5 Amps, we can see that the resistance is .28 Ohms ( compared to 2.4 ohms for the bulb). But in fact, because the bulb isn’t seeing the whole 12 Volts at which it’s rated at 60 Watts, it will be running cooler - and that means it’s resistance will be lower than it would be with the full 12 Volts, so the current draw is likely to be greater. That in turn means that the unwanted switch resistance is actually less than .28 ohms. It can be hard to measure such small resistances.
Perhaps Saisei can do a good deal on a replacement switch.

[Strebe]

Thinking about it, I recently bought from Saisei the “ Wired George “ ignition set up, which of course uses a relay to overcome the voltage drop in the primary ignition circuit caused by switch contact resistance etc.
Maybe Saisei could start to offer the Matchbox headlight relay, which we enable customers to avoid the hassle of buying direct from the US.
Just a thought!
And if course, your right that if the voltage at various points in the light circuit are measured, with the headlight on, then one should be able to identify the location if the unwanted resustance. But this has to be done under load, because otherwise the current drawn will be so low that there will be barely any voltage drop across a resistance of .28 ohms.

[ZedHead]

I think we are saying the same thing Strebe and yes if a new switch is needed I would be happy help

[johny brando]

Thinking about it, I recently bought from Saisei the “ Wired George “ ignition set up, which of course uses a relay to overcome the voltage drop in the primary ignition circuit caused by switch contact resistance etc.
Maybe Saisei could start to offer the Matchbox headlight relay, which we enable customers to avoid the hassle of buying direct from the US.
Just a thought!
And if course, your right that if the voltage at various points in the light circuit are measured, with the headlight on, then one should be able to identify the location if the unwanted resustance. But this has to be done under load, because otherwise the current drawn will be so low that there will be barely any voltage drop across a resistance of .28 ohms.

Really appreciate your thoughts & input . I've been a quiet last couple of days as I've been as i've checking bits & pieces that z1bman & Paul have suggested and there has been a positive move forward thanks to both of them & there informative & good feedback ........."now " I have 2 more volts = 10.4 v at the bulb with the lights on & 11.6 at the bulb connecter itself with it powered up ....but NOT connected to the bulb itself ! so a 1.2 v drop when it's connected. Then with - Engine running @ 2000 rpm and lights on I'm getting 11.2 v at the bulb itself & 12.6v across the battery at the same 2000 rpm ( lights off 13.7 v at the battery ) so the 60/55 bulb is performing better but it's still displaying like it's a bloody 30/45w bulb ???? Gunna try a couple of things including seeing what volts I've got going into the on/off light switch then carrying on down the line looking for voltage drop.
I don't really wanna go putting relays & this n that on the bike if it's not really required = just more to go wrong later aye ! ( I feel the wiring & switch should be able to handle a 55/60w bulb ...it might be border line but back in the day ...every one use to do it OK ) I will if I have to ...but kicking & screaming aye haha . In the mean time I'll keep looking & moving slowly forward- i hope !!!! If you think of any thing else .....we'll keep it coming as I need the help. Cheers.

[johny brando]

I think we are saying the same thing Strebe and yes if a new switch is needed I would be happy help

Thanks that man, much appreciate your assistance!!!!!!! I'm gunna check voltage into On/Off R/H switch and then down the line to the bulb. I think it will be OK though because I did completely & thoroughly strip clean & lube both switch blocks just a couple of years back & there in real good nick .....but hey ...they now be burnt or have bad connection ? ( Although i doubt the headlight had been turned more than twice in the last 2-3 years as I don't ride it at night here = lots of Big & Brain dead wildlife here ...all intent on up ending you ! haha
I'll post the finding when & if it gets nailed in the mean time ALL thoughts coming in are appreciated. Cheers Bud.

[johny brando]

when did you fit the cibie headlight ? if the ballast resistor was not removed before it was fitted the cibie light would only be as bright as a candle like the original headlight was

Thanks for the reply z1bman. The bike when i bought it was 2-3 years old & it was then a "very short wheel base version....ooouch " when I bought it in 1978 !!!! so it's didn't re-appear back on the road until I had completely rebuilt & heavily modified it all = 1981 & to be honest i don't recall if the H.4 & Cibie were prior fitted on it ??? I never got to ride it much after I built it then then as I myself had had a BIG- OFF !! just prior to completing it & I was out of circulation in & out of hospital for a good Year plus ! I'm certain of this though you were 100% right on the money.... with me having not wired the the original Ballast Resistor connections correctly when I rebuilt it & after your good diagnosis I set about correcting it . It was hooked up to the wiring ...just not correctly, so doing what you said got the voltage back up with lights turned ON from 8.4v to 10 .2 v at the headlight bulb spades with the connector plug attached ( & 11.6v at the connector plug - Disconnected from the bulb ) a great positive move forward but the headlight is still down on performance ...it performs more like std incondesant 35/40 watt bulb than a 55/60 H-4 ???? I 'm now getting with lights on & motor running at 2000rpm = 11.2v at the bulb spades & 12.6 across the battery Mmmmmm ! I'll keep chipping away at it ..hopefully maybe I'll find the secondary culprit . Thanks bud appreciate your sound advice & thought's .... keep em coming please. Cheers Lee.

[tlc]

I would check voltage to the headlight switch multi connector then output from the switch at the multi connector under the tank.
I would suspect there is some resistance in that switch as has been said. All this with no bulb connected.
If there is a voltage drop at either of these points from battery voltage a simple resistance check should give you an idea of where to look.
Theoretically there should be no resistance at all within the circuit although there nearly always will be.
Most likely ignition switch or headlight switch.