Hello everyone,
I recently purchased a 1975 R90S in very good overall condition and need assistance in trying resolve a bit of electrical mystery. First of all let me say that while I can do some basic maintenance on my bike I am a total ignorant as far as anything electrical beyond the very basics. So here is a description of the problem I have:
When trying to turn the engine off with the ignition key it will not turn off unless I press the horn button.
Interestingly enough it will turn off if I turn the key off immediately or shortly after starting the engine but not when the engine has been running for a while.
The kill switch does not respond either when I try to turn the engine off when it is warm.
Any insights will be very much appreciated. I intend to take the bike to my local dealership later on if I can't resolve the problem myself but would like to give it a try first.
Unless you have the proper wiring schematic on hand for your bike, there are several sources for one, I am afraid your best bet is to take it to the shop. Chasing wiring problems is not for the faint hearted even when a schematic is on hand.
As the bike is new to you but used, I hazard you have a case of Previous Owner's disease. Someone before you had a switch off or did some kind of wiring change and didn't do the job correctly. Now, you are the lucky guy to pay the bill to fix it.
The kill switch and horn circuits are not that complicated and because I don't have a schematic handy for you bike, I can't tell you to look in the headlight shell where all the wiring terminates to check to see if the proper wires are plugged into the proper place in the big board. Or what color wires are involved.
If you really want to take a look before going to the shop, you can perhaps find the problem yourself. All the wiring in the bike is color coded. If you remove the headlight out of the housing and look in the back at the white circuit board, you will see it is color coded. One side of the board is un switched power, the other switched. Solid color wires and striped combo color wires.
Trace the kill switch wire from the handle bar to the inside of the shell and look to see if that wire or wires from that bundle are all plugged into the proper colored spot on the circuit board. Repeat the same for the horn button side. You might get lucky and see a wire plugged into the wrong spot.
Other than that, get a good wiring schematic, the best are available at EME company, they are large, colored, numbered and plastic coated.
Hopefully the previous owner if he did do wiring work was neat and tidy and didn't leave the inside of the headlight shell and it's wiring looking like a bundle of jumping snakes. I know it is tight to work in there with fat fingers and hard sometimes to see but patience is a virtue when working on anything in there.
Yeah, I know a long rambling reply, I feel sorry for you, a nice R90S is supposed to be ridden not worked on and I HATE previous owner's disease, some people should have their fingers tied together before letting them work on stuff. LOL, Good luck. St.
Beware! I do not suffer fools gladly! St.
You have a "ground" issue. The starter power is most proabably returning through one of the other electrical systems.
Back in the day, these bikes were ridden for thousands of miles in rain and all sorts of bad weather. And then they got washed. 50 years of water on the harness connections has caused minor corrosion which MUST be dealt with. This makes the electrical system behave in weird ways. Please read the following resource...
You'll need to methodically treat every single connector (wire-to-wire, relay-to-socket, wire-to-frame) on the bike to solve the issue. The repair is very inexpensive, it simply takes a long time. But at the same time anyone can do it. You needn't be an electrical genius to do a first rate repair and get your bike back to operating 100%.
Even if this is not your issue, poor connections will make your bike impossible to troubleshoot. And so starting with rejuvenating all the electrical connections will be worthwhile. Most people that do this treatment report substantially better electrical performance.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
@14724 Thanks for your reply, I have a wiring diagram in my Haynes manual and will look it over. I will probably wait till the winter months to open this things up in my shop and hopefully will find a solution to this problem. Kind of strange that it only happens when the bike has warmed up...?
@wobbly Thanks for the link I will order the No-OX-ID as per the article and treat all the connectors I can get to. I will likely wait till the winter before starting on this once the riding weather is over here in Canada.
• No-Ox-Id is not the only anti-corrosion compound, it's simply the one I started with when working on military-grade electronics, then it showed up on Amazon. If you have a pal who is an electrician, he can proabably give you a old can of "No-Ox" or "De-Ox". It goes by many names.
But you want the professional grade compound for contractors, which chemically interacts with the brass to reverse surface oxidation. You do not want the home owner grade junk from Home Depot.
• I wouldn't wait for winter. This is something you can do every time you have a spare 15 min. Remove the headlamp reflector and pull up a stool and a bright floor lamp. Using a pair of needle nose or duck bill pliers, unplug ONE wire at a time. Add a dab of compound to the inside of the female terminal (or outside of the male), then slide it right back onto the terminal where it came from. Easy and simple.
No one sits down and does the whole bike, it's all slowly completed in sections. Obviously you may wish to wait until you need to remove the fuel tank for other reasons to attack the important connectors and grounding points under the fuel tank. And don't forget inside the tail lamp. The rectifier and alternator terminals behind the front engine cover is another location that may need to wait. You get the idea... if you go into the tool tray, then do the multi-pin harness-to-harness connector while you're there.
Slowly you'll start to see operating improvements as the electrical systems (charging, lighting and ignition) start to operate as designed. But, the biggest "bang for the buck" is inside the headlamp shell.
Regards
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
@wobbly Again thanks for the information, however with the 90S you have to remove the fairing and disconnect the clock and volt meter in order to gain access to the headlight compartment. I am just about to leave for a trip down South with my other bike (1200 RT) so will attack this project when I come back. Will keep you posted on my progress if any when I am back in the shop.
Have you made any progress? St.
Beware! I do not suffer fools gladly! St.
@14724 I finally got around to look under the tank of my 90S and saw that the electronic ignition installed by the previous owners is the Boyer Bransden unit. I contacted the company help line and they mentioned that the issue I described earlier is in fact related to the ignition module. They provided me with a revised writing diagram that should resolve the problem. I will probably get to it later on this winter.
Good of them to help out, I am glad you are making progress and thanks for the update. Good luck, St.
Beware! I do not suffer fools gladly! St.
@14724 I finally got around to look under the tank of my 90S and saw that the electronic ignition installed by the previous owners is the Boyer Bransden unit. I contacted the company help line and they mentioned that the issue I described earlier is in fact related to the ignition module. They provided me with a revised writing diagram that should resolve the problem. I will probably get to it later on this winter.
• I've been troubleshooting and installing the Boyer units on British bikes since about year 2000. Their electronics are first rate, but their wiring schematics do leave a lot to be desired. And those poor schematics account for about 95% of customer installation issues. They like to use the "ground symbol" in their schematics, which leads those without formal training to think they can simply attach that wire to the motorcycle frame... which is ridiculous.
As I remember, I took the power return on my Boyer control box all the way back into the headlamp and connected it to one of the 3 or 4 empty terminals within the Brown section of the multi-color circuit board. That's the best/closest ground/return point for newly added lights and electronics on an Airhead of your model year.
• The second common mistake is that people fail to follow-up installation with strobe timing. Boyer instructions describe a procedure that will allow the bike to crank and run. But that is ONLY for the initial start-up in the shop, not for riding around. The timing at that point is most definitely not finalized. It must be followed up by 1. strobe timing on the "Fast" mark, and 2. at a very high 5000 RPM to insure the ignition reaches full advance.
• Additional to all of that is an 'Achilles Heel' built into the late 1970's/ 1980's Airhead wiring harness design. The main power line from the battery to the ignition switch travels through the Starter Relay (which on the /7 bikes is often further complicated by the under-tank front brake reservoir leaking corrosive brake fluid directly onto the relay contacts). Thus, any degradation of the Starter Relay connection from 50 years of dirt, rain water, soapy wash water and/or brake fluid will lead to faulty power connections for the entire bike.
The problem for the EI (as previously described) is that a 1-2 milli-second power outage leads to a 2-3 second ignition outage as the EI reboots it's software. This is then reported to the rider as a severe mis-fire and 'stumble' felt in the seat and controls.
► If your Starter Relay contacts look like this, then you needn't go any further until you replace your Starter Relay and coat the new relay's terminals with an electrical anti-oxidation compound, such as No-Ox-Id.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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