Head Light relay Help!

[Rickrod3]

Hey Guys:
The other day I was blowing the head light fuse after jumping out the contacts on the head light relay was able to get the head light to work and the fuse would not blow.

I think the relay is a good thing, so you can start the bike with out that load of the head light.

So I picked up a automotive headlight Relay.
12 volt coil.

Installed it and started the bike the head light would not come on.
All contact and coil connections are correct.
Bench tested it and with 12 volts on the coil the contacts close which I have the blue and red wires connected to.
I know they have stripes just do not remember what they are right now

Coil wires are the black = ground and yellow from the generator.
When I start the bike I do not get 12 volts from yellow to ground only 7 volts.
I tested the ground by going from ground to the main fuse and got 12 volts.

I traced the yellow wire back to the connector from the generator it has three whites and the yellow. I get continuity from that connector to the relay.

The generator works as far as charging I can start the bike and the voltage goes from 12.4 to 14 volts.
Is the 12 volt coil the right voltage?
Trying to help myself but I cannot find any further information in the manual about this yellow wire.

Thanks
Rick

[psycoreefer]

Someone who knows for sure will probably jump in but I think the reason you don't see 12v is that the wires from the generator are AC, not DC, and the voltage reg/rectifier change it to DC for the rest of the electrical system.

[cywelchjr]

It may be the diode is bad. That will keep the relay from working. 14v 1w diode will do the trick as long as you get it in there the right way. Actually I may have put an 18v but it just needs to half rectify the line to give dc pulses to the relay, once it's setup right it will latch on.

[Rickrod3]

It may be the diode is bad. That will keep the relay from working. 14v 1w diode will do the trick as long as you get it in there the right way. Actually I may have put an 18v but it just needs to half rectify the line to give dc pulses to the relay, once it's setup right it will latch on.

Okay it makes sense that it would be an ac signal. The relay I have has a 12volt DC coil.
How would I wire the diode in?
I'll take a stab that it is in series with the yellow wire coming from the altenator.

Rick

[Rickrod3]

Diode Search

I did a search for diode information and, I saw that on some of the wiring diagrams it shows the diode on a white wire.
My bike an F uses a yellow wire the wiring diagram does not show a diode in it.
Could it be in the relay here is a picture of what I'm meaning.

http://s910.photobucket.com/albums/a...IMG00056-1.jpg
Just want to make sure before I start to remove all the tape on the harness.

Could someone also explain the jumper to keep the light on?
sorry cannot seem to wrap my head around it.

Rick

[bikerphil]

Pretty sure the 78-79's have the diode in the factory relay itself, the 80-81's have it buried in the harness.

[3Phase]

Rick, the Yellow wire is only supposed to have 6 ~ 7 volts AC on it. The White wires carry 12 ~ 14 AC you can use to activate the 12 volt relay.

You'll to have to join the wire for the relay coil and a diode (to turn the AC into DC) with one of the White wires at the Regulator/Rectifier connector. That's the way the late-model bikes do it. The late-model bikes don't use the Yellow wire at all; just there, like an appendage.

Oversimplified, the XS alternator has 3 coils in it hooked up in a Wye. I think a picture will show it better:-

http://www.allaboutcircuits.com/vol_6/chpt_4/8.html


The White wires are connected to the points of the Wye and they get the voltage from two coils at a time, in series, then run over to the rectifier.

The Yellow wire isn't shown in the picture but it is connected to the common connection point in the middle between all three coils. It only 'sees' the voltage of one coil at a time.

1 coil = 7 volts.
2 coils = 14 volts.

Have fun and try not to let any of the smoke out of the wires!


Regards,

Scott

[brcree]

Head light woes

I found my diode to be built into the relay that is up next to the steering neck. I have a 81 sx SH. Took the cover off the relay and its a tiny round gray colored item with black stripe on it. This diode is supposed to not let current go back to your reg. The unit will work with out it (shorted) just don't ever hook up jumper cables backwards or you will fry your reg. unit.

[3Phase]

I found my diode to be built into the relay that is up next to the steering neck ... don't ever hook up jumper cables backwards or you will fry your reg. unit.

Good tip about the jumper cable polarity!

My headlight relay wouldn't work without the discrete inline diode on the White wire. The diode inside the headlight relay is a latching diode. Think of it as a belt and suspenders type of system.

The White wire/diode normally keeps the relay coil energized while the charging system is running and the voltage is up.

The latching diode keeps the relay energized until you turn off the ignition switch. The headlight won't flutter on and off when idling at an intersection and the voltage drops or suddenly go out entirely at night in a blind corner if the charging system fails.


Regards,

Scott

[randy]

Scott;

Then there must be a difference in the relays themselves between years, 'cause my 79 (and I beleive the '78 but can't say for sure) does not have a diode in the yellow circuit.

[Rickrod3]

Randy:

I don't know if it matters when I took the readings and got the 6.5 to 7 volts my meter was on the DC. scale (though I was going to get DC voltage)

I'll try to take a reading using the AC scale

Rick

[3Phase]

Rick, the AC wave form on the Yellow wire 'looks' sort of like DC to a test meter.

scott;

then there must be a difference in the relays themselves between years, 'cause my 79 (and i beleive the '78 but can't say for sure) does not have a diode in the yellow circuit.

Randy, there is no diode in the 78/79 Yellow wire. It's a Wye neutral floating 6 ~ 7 volts above vehicle ground. There are different relays but I don't know absolutely positively 100 percent for sure on a stack of Bibles what the differences are besides part numbers and the schematics.

I have tried using late-model 12 volt relays on a 1979F and none of them worked with the voltage on the Yellow wire. I assume that a 78/79 relay would work but eventually fail in a late-model bike.

78	 	5	360-81950-10-00	relay assembly

79f/sf		5	2h7-81950-10-00	relay assembly

80g/lg/sg	7	3h5-81950-00-00	relay ass'y

81h/lh/sh	7	3h5-81950-00-00	relay assembly

82j		7	4u8-81950-02-00	relay assy

78/79 use the Yellow wire with 6 ~7 volts and two different part numbers.

80/81 use the White wire with a diode, 12 volts and the same part numbers.

I haven't studied the XJ schematic so I don't know how its unique relay is connected.


Regards,

Scott

[randy]

? I'm using an '81 relay in my '79. No diode in the harness, it works fine.

[3Phase]

? I'm using an '81 relay in my '79. No diode in the harness, it works fine.

Now that is interesting. I tried three different late-model relays in a '79: epic fail.

All three were Hitachi relays. One had a bad coil, the other two worked fine at 14 volts but wouldn't close at 7 volts. I dunno....


Regards,

Scott

[Rickrod3]

Are these the diodes?

http://s910.photobucket.com/albums/a...1.jpg&newest=1

If not what are they?

I was thinking maybe the relay can be repaired?

The coil is not open.
The relay was blowing out the fuse as soon as the engine was started.
the contacts look fine.

The 2 componets in question have the following ratings
2W 10 0 ohm sign K
Micron 8.2

It might be easier or worth a try to replace those parts if I knew what to ask for.
One of them looks to have a burn mark on them.

TIA
Rick