Safety Relay and Light Checker wiring question

ApolloStaar

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Hey everyone, in need of a little wiring help, I'm completely rewiring my stock '75, new wiring harness et al. Everything is pretty much connected. What is the function of the Safety Relay and the Light Checker? Do I need the safety relay box and light checker box for the electrical to run properly, or can I bypass them(and how)? Both are missing, right now there is nothing attached to the connector blocks on the new wiring harness. I'm running a Boyer/Bransden electrical ignition(not sure if this matters), and no PMA kit, it's still electrical start/kick start. And still trying to get my turn signals to work, any tricks? Any advice appreciated. Thnx!
wiring pic.jpg
 
Hi, Apollostaar, this is your first post so welcome to the forum, you have come to the right place for help! I have 1978 XS650 SE with Boyer Bransden ignition and the route I went was to rewire the bike completely - the stock wiring was so hacked about, that seemed the easiest way for me. You could take a look at my simplified wiring diagram here: http://www.xs650.com/threads/miss-november-xs2-tribute.55057/page-40#post-632045

But to answer your questions, the safety relay is to stop the starter being engaged if the engine is running. That seems useful, so I kept it. The light checker is there to warn you if your headlamp bulb fails - if I got that wrong, somebody will correct the error - but anyway, I simply removed it. Which saved me a whole bunch of wires. The 1979 bike also had a reserve light unit, which your bike probably doesn't, the function was to illuminate the main beam in the event of the dip failing. Seems daft, so removed to save more complexity. Also, removed the flash cancel unit - your bike might not have this? - which used feeds from speedo etc to work out when to cancel the indicators. Saved a lot more complexity.

There are lots of knowledgeable folk here who will ask you which wiring harness you have and then tell you which colour to connect where to make it all work. I used to be in complete awe of electrics but having now rewired this bike and an old Triumph have come to realise that although it all looks very complex, in fact it's not. For the turn signals, all you need is a wire from the battery > fuse > flasher relay (under front of petrol tank) > flasher switch which them completes the circuit to left or right flashers > ground. You can follow these through - a multi-meter is very useful to check continuity. Good luck!
 
If you still have the factory turn signal flasher, it was designed to work with four stock sized turn signal bulbs @ 23 watts each I think. I see you have aftermarket signals fitted. If their bulb wattage isn't the same then that's probably why they aren't working.

I don't think a '75 model had the RLU. The only light checking device I see on the wiring diagram is for the brake light. It's called the stop light checker and is the early 3 wire unit. It can simply be left off with no wire jumping required.

I wouldn't do away with the starter safety relay. You could do a lot of damage if you accidentally hit the starter button while tooling down the road at 40 or 50 MPH.
 
The light checker is there to warn you if your headlamp bulb fails - if I got that wrong, somebody will correct the error - but anyway, I simply removed it. Which saved me a whole bunch of wires. The 1979 bike
Is it that simple to "simply remove" the light checker unit. I have noticed the 7 wires in that plug and searched the forums as to whether the light checker can just be unplugged or does that require additional jumping or a mod ? On my 79 Special II
 

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No, not with your 7 wire unit. Only the simpler 3 wire unit can just be removed. Your 7 wire unit monitors both the brake and tail light. Tail light power passes through it so if you simply remove it, the tail light won't work anymore. You will need to install a jumper wire to restore power flow to the tail light. If you study the wiring diagram, you'll see tail light power comes from the ignition switch to the light checker on a blue/yellow wire. Tail light power runs out of the light checker on a blue wire to the tail light. You will need to jumper the blue/yellow to the blue in the harness plug once the light checker is removed.
 
Nice, I'll follow that schematic and great advice on a monitor at lunch break. Sounds like good news !
-R
 
Is it that simple to "simply remove" the light checker unit. I have noticed the 7 wires in that plug and searched the forums as to whether the light checker can just be unplugged or does that require additional jumping or a mod ? On my 79 Special II
Sorry, Randy, should have explained more fully. As said, I completely rewired the bike to a much simpler system. For me it was a simple decision to omit the light checker. I cannot answer whether removing the checker from a standard loom would require fitting a jump.

PS I see that while I was typing, 5T has put a much better answer.
 
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All good Raymond. This is just more learning. As the years have gone by with a few XS's now. With the aid of this forum and members assisting, my own knowledge and understanding of the 70's electrical systems has improved leaps and bounds.
That is really nice !
-R
 
The safety relay does more than prevent the starter from working with the engine running. It also stops the starter as the engine stats so toi prevent starter being over run by the engine. This damages the gears between the starter and engine. If you want you can bypass it I. I wouldn't leave it that way. I would get the right relay or wire in a lighting relay.
To bypass, on the wire plug at the safety relay you will find two Red/White wires. One is power to the relay, the other is power out to the starter relay. The safety relay opens the contacts on these R/W wires.
To replace you need one of the 5 wire lighting relays. You need to build some jumper wires from the plug to the relay. Hook one R/W wire to terminal 30, hook the other to 87A. Hook the yellow wire to 86. Hook 85 to ground.
This only works on the early bikes before the headlight section was added to the safety relay.
Leo
 
Hi, Apollostaar, this is your first post so welcome to the forum, you have come to the right place for help! I have 1978 XS650 SE with Boyer Bransden ignition and the route I went was to rewire the bike completely - the stock wiring was so hacked about, that seemed the easiest way for me. You could take a look at my simplified wiring diagram here: http://www.xs650.com/threads/miss-november-xs2-tribute.55057/page-40#post-632045

But to answer your questions, the safety relay is to stop the starter being engaged if the engine is running. That seems useful, so I kept it. The light checker is there to warn you if your headlamp bulb fails - if I got that wrong, somebody will correct the error - but anyway, I simply removed it. Which saved me a whole bunch of wires. The 1979 bike also had a reserve light unit, which your bike probably doesn't, the function was to illuminate the main beam in the event of the dip failing. Seems daft, so removed to save more complexity. Also, removed the flash cancel unit - your bike might not have this? - which used feeds from speedo etc to work out when to cancel the indicators. Saved a lot more complexity.

There are lots of knowledgeable folk here who will ask you which wiring harness you have and then tell you which colour to connect where to make it all work. I used to be in complete awe of electrics but having now rewired this bike and an old Triumph have come to realise that although it all looks very complex, in fact it's not. For the turn signals, all you need is a wire from the battery > fuse > flasher relay (under front of petrol tank) > flasher switch which them completes the circuit to left or right flashers > ground. You can follow these through - a multi-meter is very useful to check continuity. Good luck!
Hi, Apollostaar, this is your first post so welcome to the forum, you have come to the right place for help! I have 1978 XS650 SE with Boyer Bransden ignition and the route I went was to rewire the bike completely - the stock wiring was so hacked about, that seemed the easiest way for me. You could take a look at my simplified wiring diagram here: http://www.xs650.com/threads/miss-november-xs2-tribute.55057/page-40#post-632045

But to answer your questions, the safety relay is to stop the starter being engaged if the engine is running. That seems useful, so I kept it. The light checker is there to warn you if your headlamp bulb fails - if I got that wrong, somebody will correct the error - but anyway, I simply removed it. Which saved me a whole bunch of wires. The 1979 bike also had a reserve light unit, which your bike probably doesn't, the function was to illuminate the main beam in the event of the dip failing. Seems daft, so removed to save more complexity. Also, removed the flash cancel unit - your bike might not have this? - which used feeds from speedo etc to work out when to cancel the indicators. Saved a lot more complexity.

There are lots of knowledgeable folk here who will ask you which wiring harness you have and then tell you which colour to connect where to make it all work. I used to be in complete awe of electrics but having now rewired this bike and an old Triumph have come to realise that although it all looks very complex, in fact it's not. For the turn signals, all you need is a wire from the battery > fuse > flasher relay (under front of petrol tank) > flasher switch which them completes the circuit to left or right flashers > ground. You can follow these through - a multi-meter is very useful to check continuity. Good luck!
Thanks for the useful information. Good diagram!
 
If you still have the factory turn signal flasher, it was designed to work with four stock sized turn signal bulbs @ 23 watts each I think. I see you have aftermarket signals fitted. If their bulb wattage isn't the same then that's probably why they aren't working.

I don't think a '75 model had the RLU. The only light checking device I see on the wiring diagram is for the brake light. It's called the stop light checker and is the early 3 wire unit. It can simply be left off with no wire jumping required.

I wouldn't do away with the starter safety relay. You could do a lot of damage if you accidentally hit the starter button while tooling down the road at 40 or 50 MPH.
Good info, thanks! Now just need to find a Safety relay! Can't find a new one anywhere. :(
 
The safety relay does more than prevent the starter from working with the engine running. It also stops the starter as the engine stats so toi prevent starter being over run by the engine. This damages the gears between the starter and engine. If you want you can bypass it I. I wouldn't leave it that way. I would get the right relay or wire in a lighting relay.
To bypass, on the wire plug at the safety relay you will find two Red/White wires. One is power to the relay, the other is power out to the starter relay. The safety relay opens the contacts on these R/W wires.
To replace you need one of the 5 wire lighting relays. You need to build some jumper wires from the plug to the relay. Hook one R/W wire to terminal 30, hook the other to 87A. Hook the yellow wire to 86. Hook 85 to ground.
This only works on the early bikes before the headlight section was added to the safety relay.
Leo
Great info, thanks! Now just need to find the right 5 wire lighting relay.
 
Hi,

I just did this. I used just the SSR and not the lighting relay. A replacement relay, a 6 volt one with five tabs, i.e., you want an 87 and an 87A connection on the relay, should work too. You want the yellow PMA voltage to disconnect power to the solenoid. Six volts spec for relay is important, 12V may not work correctly. Here is a link for them:

https://www.ebay.com/itm/2-LOT-TEMC...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Starter Motor & SSR Relay Wiring Diagram - GPM.jpg
 
Hi,

I just did this. I used just the SSR and not the lighting relay. A replacement relay, a 6 volt one with five tabs, i.e., you want an 87 and an 87A connection on the relay, should work too. You want the yellow PMA voltage to disconnect power to the solenoid. Six volts spec for relay is important, 12V may not work correctly. Here is a link for them:

https://www.ebay.com/itm/2-LOT-TEMCo-Industrial-6-V-30-40-Amp-Bosch-Style-S-Relay-SPDT-Automotive/283063032038?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

View attachment 161859
Thanks for the info and diagram. Will it work on a '75? My bike does NOT have a PMA kit installed, it's stock(aside from the electronic ignition) and still runs off the battery.
 
Hi,

I just did this. I used just the SSR and not the lighting relay. A replacement relay, a 6 volt one with five tabs, i.e., you want an 87 and an 87A connection on the relay, should work too. You want the yellow PMA voltage to disconnect power to the solenoid. Six volts spec for relay is important, 12V may not work correctly. Here is a link for them:

https://www.ebay.com/itm/2-LOT-TEMCo-Industrial-6-V-30-40-Amp-Bosch-Style-S-Relay-SPDT-Automotive/283063032038?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

View attachment 161859
Hi there, finally got my safety relay per your eBay link, thank you, but now having trouble trying to figure out what wire goes where. On my new wiring harness there are 2 connector blocks(not sure which one to use, or both?) that have wires coming out of them and seem to be for the safety relay, some wires from the harness are different colors than the wires connected to the new safety relay. If you have a minute, can you help me figure out which wires go where? I'm including pictures of the wires coming from the 2 connector blocks from the new wiring harness just installed on the bike and a picture of the new eBay safety relay block showing the colored wires. I understand that the numbers on the relay correspond to the slots where the wires go, but some of the wires on the harness don't match with the corresponding numbers on the new relay. Any info helps, thanks, really appreciate it!
labeledwiring1.jpg
wiring2.jpg
 
No, not with your 7 wire unit. Only the simpler 3 wire unit can just be removed. Your 7 wire unit monitors both the brake and tail light. Tail light power passes through it so if you simply remove it, the tail light won't work anymore. You will need to install a jumper wire to restore power flow to the tail light. If you study the wiring diagram, you'll see tail light power comes from the ignition switch to the light checker on a blue/yellow wire. Tail light power runs out of the light checker on a blue wire to the tail light. You will need to jumper the blue/yellow to the blue in the harness plug once the light checker is removed.
Guys.. New to this forum as I'm a very long time owner of a 79 XS750. I came across this post after hours of searching on the topic of a light checker on my bike. Most guys haven't come across it on their bikes and my Clymer wiring diagram doesn't show this relay. Thank you for posting this info and the wiring diagram as its the first one to really show what's going on. I only have 6 wires compared to the 7 wires on the 650's. I've jumpered the blue & blue yellow but my next question is what to do with the black/red lead to the warning light so it doesn't come on when I remove this relay. Any help is appreciated!
 
I don't think the warning light will come on if you remove the relay. On the 650, it doesn't. The relay is what sends a ground to the warning light to complete it's circuit and make it come on. No relay and that can't happen, so the light should remain off.
 
I don't think the warning light will come on if you remove the relay. On the 650, it doesn't. The relay is what sends a ground to the warning light to complete it's circuit and make it come on. No relay and that can't happen, so the light should remain off.
Thanks 5twins! Any idea why this relay would be kicking out 6 volts to the yellow wire or on the 650 wiring diagram its the green/yellow? This leads to the brake (not tail) light. I'm wondering if my relay is bad because it makes no sense to me how 12v is being converted to 6v unless something isn't right in the relay.
 
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