headlight relay electrical short in 82 XJ550

After reading all the relevant posts here and getting the electrical diagrams, I found that elusive electrical short in my headlight relay. Its case was beat up and bent and the short was coming from there. The replacement relay is either $84 from Yamaha. So I'm trying a SPST relay for $0.88:

339-098 Omron Relay 12 VDC 15A $0.88
http://www.partsexpress.com

Hope this helps the next guy.

 

post back with results and how you connected it up. That will help people more in the future.

 

here are the results. I think it worked, but since I inherited the bike with the short, and the headlights never worked in the first place, I'm not sure what it is supposed to do.

With my new relay, the headlights come on, but they don't turn off during cranking of the engine. This is incorrect observed behaviour, right? But are they supposed to do either:
A. Turn on except when cranking (thus can be used to light up the road side in an emergency without the engine running)
B. Never come on except when the engine gets up to speed?

So I ordered a new standard relay, and the behaviour is the same. So it appears that the relays work, but that the circuit powering its coil is always ON. Any ideas what could cause this? What is the theory behind the primary side? Is it actuated by the starter button? Or is it sensing voltages with solid state gadgets? What am I up against here?

 

The headlight will SOMETIMES come on during cranking, as the relay has a certain "trigger" voltage level that latches the relay open, and thus the headlight turns on. Cranking the engine with the starter motor will SOMETIMES allow that trigger voltage to be reached, and the headlight will come on and then remain on until the key is turned off (which de-energizes that circuit and allows the relay to close). When you FIRST turn the key to the ON or RUN position, BUT DO NOT CRANK THE BIKE, the headlight should be off. It may or may not come on during cranking, but always will as soon as the engine fires. The headlight will not turn off UNTIL THE KEY IS TURNED OFF......this means that if the engine dies/stalls/etc. with the key on, the headlight will remain on unless you turn the key off!

 

I concur. My experience with the headlight control circuit is exactly how chacal explained. The OE headlight relay has a diode in it that back-feeds power to the latching circuit to keep it alive once energized.

 

Question about setting up that relay. The one I have now is set up differently than the one pictured when I search for that relay on Parts Express. Mine has its prongs parallel to each other, and the pronged section slides into a matching receptacle. How do I convert to that layout?

 

Hey Amitlu.....I have some good used original relays available, that's the easy way to solve the problem! Let me know if you're interested.

 

Oh, big time. Is it the headlight relay for sure? If so, I'm waaaay interested.

 

amitlu.....check your inbox, you've got mail!

 

Posed this question to chacal over PM, but I thought I'd ask for help here, too:

I went to double check that bad relay this evening, and lo and behold, I think I may have the wrong relay. The colors going to this one are: Red with white tracer, red with white tracer, black with yellow tracer, and sky blue. I checked my CD, and it's only referred to as "relay" on the wiring diagram. It's located on my bike under the gas tank, right where the headlight relay should be.

Any thoughts?

 

That's the side-stand position relay..............

Got those, too!

 

Haha, you're a man of many relays. I had a sneaking suspicion that may be what it was.

Next question, then. When I swap that out with one of the relays on the opposite side of the battery and turn the key, the headlight comes on but the bike won't start. But when I swap them back, the bike starts and the headlight stays off. Any reason a finicky side-stand relay would cause that?

 

Yes, the bike is wired so that it will not start/run with the side-stand in the DOWN (on the ground) position if the bike is in gear and the clutch lever is not pulled in.

The entire "safety" mechanism on these XJ bikes is very thorough, and thus very complicated. There are switches, wiring, relays, and a diode block (and some relays also have an internal diode) that all work together to allow certain actions and dis-allow other actions. As such, there are many possible trouble spots.

One (or both) of those relays may be bad. Unfortunately I don't know enough about the internal circuitry of each relay to be able to fully answer your question. However, when you turn the key on (without starting or even cranking the bike), the headlight should be OFF. Only when cranking (sometimes) and running (all the time) should the headlight operate. It will continue to operate once it has been lit even if the engine dies. The headlight should not go off untilt he key is turned off.

The side stand relay should not allow the bike to crank (or maybe only to not fire????) when the side-stand is down, and it will kill the bike if put down while the engine is running IF THE BIKE IS IN ANY GEAR (it will allow starting/running if in neutral). I think. Others may correct me on this.

The service manual specs for both the side stand and the headlight relay specify 100 ohms resistance, and it is beyond the scope of mere words to describe the testing procedures for this. You'll need a factory service manual or the Haynes manual for your model (P.S. yes, you guessed right, I sell those too!); both have great schematics and testing procedures and diagrams.

BTW, here's some info that I consider reliable (and invaluable), but use at your own risk:

**********

There are at least 4 relays used on various XJs that look identical: two
different versions of the headlight relay, the ignition cut-off relay and
the sidestand relay. While the connectors will allow you to mix and match,
the relays are different internally. For example, a headlight relay has the
identical pin-outs as a sidestand relay, but the coil is a much higher
resistance. The headlight relay resistance is around 90 or 100 ohms while
the sidestand relay is less than 1 ohm. If you were to install a sidestand
relay in the headlight relay circuit, it would likely work for a short while
and then burn out the coil.

Also, there is no diode in the relay to latch it closed so the headlight
would turn off when the engine quit running even with the key on. The
contacts may be rated for different currents. The ignition cut-off relay is
wired completely different inside and mixing the other two will result in
either the circuit not working or destruction of the relay or both.

So, how to tell them apart? The logical thought is to look at the number
stamped on the relay. Unfortunately Yamaha outsourced the relays and
used different manufacturers at different times.

For their own ease of identification, they seem to have used a color
code system. On the connector side of the relay, look for a dot of paint:

Yellow: Headlight relay for most XJs that have them
Red: Headlight relay for XJ900*
Blue: Sidestand relay
none: Ignition cut-off relay.

NOTE THAT THIS "DOT OF PAINT" MAY HAVE RUBBED OFF OVER THE YEARS.......

Now, the locations vary by model, but on a 750 Seca the headlight relay
(Yellow) is behind the left side cover, the ignition cut-off relay (none) is
below the tank at the rear and the sidestand relay (Blue) is below the tank
on the left side of the frame just rearward of the coils.

*The "Red" XJ900 relay will work in place of the "Yellow" relay but the
headlight will not latch on when the engine dies.

AND

If the dot of paint is not found, then it's an ignition cut-off relay. (None
= no paint dot ;-)

The resistance specified is for the coil. The contacts should have either no
resistance (when "closed", ie power applied to the coil) or infinite
resistance (when open, ie loose in your hand). In the case of a yellow
headlight relay, there will also be low resistance in one direction between
the coil and one of the contacts but infinite resistance in the opposite
direction of those two contacts. This is due to the aforementioned internal
diode that latches the relay closed once the engine starts. Same with the
ignition cut-off relay: the coil is internally connected to one of the
contacts and grounded through a diode.

Now, as to which contact is which: they are not marked on the relays
themselves. Best to consult the XJCD wiring diagram or the relay test
procedures in the factory manual to verify for yourself with a picture. So,
for example, the headlight relay coil will be the two terminals that connect
to the white and black wires, respectively. The contacts are the ones
connected to the Red/yellow wire and the Blue/black wire. The diode conducts
when forward biased from the blue/black to the white (ie +12v applied to
blue/black).

With the ignition cut-off relay, the two red/white wires are the contacts.
The coil is connected internally between one of those and the blue/yellow
wire. There's also a diode, forward biased from the blue/yellow to the light
blue.

The sidestand relay is the most straight forward in that it has no internal
diode and all the wire colours are different. The coil is between the
red/white and blue/yellow wires. The contacts are between the red/white and
black wires.

 

The headlight relay works like most relays - the secondary (wires for the headlamp) is closed when the primary (alternator input) is energized. It has an added diode to latch it on so the light stays on even if alternator output stops (bike stalls).

The sidestand relay works a bit backwards. The secondary (wires to short out the TCI trigger) is closed when the primary (sidestand switch, clutch etc) is not energized. So, if you put it in place of the headlight relay the headlight will be on until the bike starts.

If you put the headlight relay in the socket for the sidestand relay it will only let the bike run in an UNSAFE condition (bike in gear, sidestand down, clutch not pulled). The bike won't start if the clutch is pulled, or the bike is in neutral.

So, bottom line is - swapping them is unsafe. And if you do get it started without having an accident the headlight will go out.

Interestingly though, since when you swap them the headlight comes on but the bike won't start you've probably proven that both relays are functioning properly.

 

I've looked at the relay you purchased for the headlight. It appears to be a NC relay - IE works like the sidestand relay. If so, the headlight will be on until you get the bike running at which point it will turn off (assuming the alternator supplies the right trigger voltage).

Remove the relay from the motorcycle. Check continuity between posts 1 and 4 - if there is continuity then this relay definitely won't work for your purposes.

 

Well hmm, I'm way confused now. As far as the sidestand relay goes, I can't start the bike with it down, so maybe the relay I tried swapping is actually the one that needs replacing?

I assumed it was the sidestand relay that was bad because the headlight wouldn't come on when it was in its original position, and the bike wouldn't start in its new one. But maybe it's like MiCarl said and the sidestand relay is doing its job and I'm either looking in the wrong place or looking at the wrong part to replace.

Chacal, I'll write down the paint dots and track down which relay I was swapping with. I think that may go a long way in figuring out what's up.

Yay electronics!

Thanks for all your help, guys. I'm just sure I'll get to the bottom of this.

 

Welcome to the club!

If the sidestand relay is operating properly, you should NOT be able to start the bike with the sidestand on the ground ("down") UNLESS THE BIKE IS IN NEUTRAL. If the tranny is in neutral, then you can start the bike, but as soon as you attempt to put the bike in gear (with the side stand down) the ignition will quit.

If the sidestand is down, and the bike is in gear, then you can only start it with the clutch lever pulled in.

The above statement is predicated upon the clutch safety switch operating correctly.

I think all of the above is correct.......

 

Hey, chacal, you changed your avatar.

 

I know....now I'm hauling butt, really red-lining!

And it indicates just how fast I'll ship out orders of XJ parts to people!

BTW, if it makes any difference, I was actually inspired to even put up an avatar (the one before was the website's "default" avatar) by your own head-bangin', rockin' and a-rollin', gear-bangin' avatar.

At least, I think that's a guitar you're holding onto......

 

All good there. Maybe I just need to track down the headlight relay for real and take a look at/replace it?