Electrical gremlins... headlight relay

Sorting out a couple electrical issues and one includes a bad headlight relay. I'm trying to locate one, but I'm also seeing conflicting advice as to where the headlight relay actually is. I know it's the 3H5 relay with the yellow Mark, but my Yamaha and Haynes manuals place it with the flasher unit underneath the rear of the fuel tank. On the forum it's said to be underneath the TCI at the left side cover? I'm either seeing conflicting information between the headlight and ignition cut off/neutral relay, or I've confused myself...

 

go with the book
the one in the rear of bike is side stand relay
add you bike to your profile

relays can be poped open and cleaned

 

Yep. The headlight relay is right next to the self canceling unit under the tank.

 

Just so you know, the book isnt completely right. I dont know if it got moved at some point but my headlight relay was under the left side cover. Until i removed it and bypassed it because the relay was corroded to death. Mines a canadian model so maybe thats why?

 

Other electrical issue are the two vacant connectors within my headlight. The red one comes straight out of the wiring harness and carries 12 volts, while the double brown one comes out of both the other half of the wiring harness, while also splitting off from the main instrument cluster connector and carries no current. Bike's electronics all seem to be functioning fine, but I'm assuming at least one of these needs to be grounded? Wiring diagrams aren't helping me...

 

wire digram shows brown wires as turn signal wire.
also shows an unused connector red wire note 5 models J & RJ only

 

Did you locate a relay to replace the faulty one? I've got a 750 and the headlight relay just died. It's labeled 3H5-00 and apparently that's been discontinued. Are there any specs on that relay or any known alternatives?

 

I bypassed my faulty one. However you must be aware that doing this puts extra load on your starting circuit, since the headlight will now always turn on as soon as the ignition is switched on. Make sure your battery is good and checking the charging system probably isn't a bad idea.

 

That^^^ is a really bad idea. You need every volt the battery has to make sure you start the engine without damaging the battery by running it down to a low-voltage condition.

You should do this instead:

HCP429 OEM main HEADLIGHT RELAY. For all XJ550, XJ650 (except Turbo), and XJ750 Seca models. Small metal "cube" type relay has 3H5 inked on the top face and has a yellow-painted locking tab for identification.
$ 109.95

HCP16240 Aftermarket main HEADLIGHT RELAY. For all XJ550, XJ650 (except Turbo), and XJ750 Seca models. Small plastic "cube" type relay fits properly and functions like the original, but it will not "latch" like the original....meaning, if the engine dies, the headlight goes off. If that feature is not important to you (and many people do not even realize that the original relay has such a feature!), then this lower-cost substitute is for you.
$ 24.95

Or hit up Ebay for a used replacement.

 

Got a $20 one off eBay and it's working just fine now.

 

I tried searching both of those part numbers for the relays and am not seeing anything on part stores or on Google.

 

The banner at the top right of every page directs you to the catalog for XJ4ever. Chacal (Len) is the number one reason so many of these bikes are still on the road in a safe and reliable condition.

You can contact Len at info@xj4ever.com or start a conversation to let him know which parts you are looking for.

You won't find better customer service or parts anywhere else.

 

I'm wondering why there are 3 relay assemblies on this diagram. The 3H5-00 model that was in my is unavailable and discontinued, but can I replace with one of the other two?

https://www.yamahapartsandaccessori...ernumber=#/Yamaha/XJ750RH_-_1981/ELECTRICAL_2

Still waiting to hear back from Len as well. It's only been half a day

 

Len will get to you before you know it. I've never had it take longer than a day, and that was on a weekend.

 

..how does one bypass relay ? i tried blue blk wire into red yellow wire.with no result, however this was at back of bike left hand side covered .not the under tank relay

 

bypassing relays in this link

The Ultimate Relay, Switch, Sensor, and Diodes Guide


Headlight relay:
- bypass the relay by connecting the Blue wire with the black tracer stripe directly to the Red wire with the yellow tracer stripe.

Starting/Ignition Cut-Off/Neutral Safety relay:
- unplug the safety relay which disables the whole bloody mess but DO NOT leave it that way, fix it right!

Sidestand (kickstand) relay:
- unplug the safety relay which disables the whole bloody mess but DO NOT leave it that way, fix it right!

 

You can see how I did it a little further up. Blue/black to red/yellow. General consensus including the manual seems to be that the headlight relay is under the tank. I still don't know why mine is under the left side cover. Mines an '80 650 Maxim.

Since my original posting I have gotten my hands on a replacement relay from a used source. As kmoe says above, bypassing it really is not the right way to go, you can cause damage to your battery by running it low, it's cheap to either order a replacement or watch for one from a bike being parted out. There's a reason they designed the relay not to kick the headlight on until the bike is started

 

Yep. To make sure that there is enough current available to spin the starter AND run the TCI at the same time. The starter is a current hog, as is the headlight.

 

..thanks y,all . using a toggle with inline blade fuse staight to positive with other into the ground..going to have to do for now...yes i have already both accident like left on after parking in daytime. plus bonus city street run with off at the nite time ride home ..thank goodness for back up batteries..

 

..strange i tried that same jumper technic in same relay spot and i got nothing?

 

Oh my gosh, I love this forum!! Thanks to Beekman for the photo of the jumper. My headlight relay is in the same place, behind the left side cover. Headlights work with the jumper, didn't work with the factory (metal case with 3H5 stamperd on it) relay. Carefully opened the relay, tried contact cleaner spray, which didn't work, and ended up running a narrow folded strip of 300 or 600 grit wet/dry sandpaper between the contacts a few times. It didn't work until I ran the sandpaper through while applying pressure directly to the contacts with a wooden shim. Now all is right, and light, with the world.

My next mod will be to replace the halogen bulbs in the headlight and driving light with LEDs to reduce the electrical load on the system. More research is necessary.

1982 XJ750RH, my second Seca 750!

 

My Headlight relay is bad. No Headlight, no lights on the tach/speedo.
Unless the engine needs to be running for headlight to work?
I put in a new fuse box and I'm getting voltage to the relay connector, but no click on the relay.
The relay for the tail lights work and turn signals work fine.

3H5 Relay and it is under the side panel like above.
1983 XJ650 Maxim

 

answering my own question, Headlight relay needs enough voltage that is only available when the alternator is running.
I am rebuilding carbs this week so looking for a way to test the relay and lights. I guess one way would be to hook up the battery to a higher power source like jumper cables to my car?
I'm going to make sure my battery is fully charged though. Don't think my charger will get the voltage high enough to match the alternator.

 

It's not a matter of voltage amplitude, it's about applying the voltage to the relay pin that goes to the alternator. I suspect the pull in voltage for the relay is less than 8V. Once it pulls in it will latch, which is why the headlight stays on when the bike stalls or sometimes when trying to start and not quite there but the headlight comes on and stays on unless you cycle the ignition key

 

ahh, thanks Rooster!, that diagram explains everything. So if I want to test the headlights and at least the latching part of the relay w/o starting the bike, I just tap short the R/Y and L/B connections or tap short the R/Y and W connection?

(still waiting for parts to rebuild carb)