Electric starter, trouble shooting hints
By Duane Ausherman
There are four main components in the starter
system. Each can be tested easily.
2. Starter switch,
3. Starter relay
4. Starter motor.
They are listed in the likelihood of failure. I suggest testing them in a different order. This info assumes that you still have original wiring and nobody has altered it.
1. Most of the starter problems are related to defective batteries and/or connections at the battery. Will your battery operate both the headlights and horn? Do the lights go out when you push the starter button? When you push the key in the instrument lights come on, but go out if the starter button is pushed. Those are typical indications of a poor battery or connection. Try loosening the connections to both terminals and reconnecting them with some grease.
2. To check the starter switch (button), remove the headlight rim assembly. Find the 4 circuit terminal block. It is a 6 terminal block starting in 72-73.
Photo by Brian Trotter, thanks.
This is the 72-73 6 terminal block type. The colors aren't in the same order as mentioned below. It matters little as you must only find the Brown/Black and they are the third one from the bottom.
The block is at the end of the
wires from the starter button. It is the place where the starter/turn
signal loom wires are attached to
other things. On one end will be the
Blue/Black wire for the right turn signal. Next the Blue/Red wire for the
left turn signal. Next the Brown/Black wire for the starter. Last is a
Green/Red wire for the front brake light switch.
The starter switch only grounds the circuit. You are going to "duplicate" the switch. Push the key in for power. If you have no terminal block, then find the Brown/Black wire from the wiring loom from the right hand control of the bars. Run a jumper wire from any good ground point and stick the other end into the terminal connector for the Brown/Black starter wire. Just poke it into the place where you see the set screw for a slot screwdriver.
If the starter turns, then that is proof that the starter is "good," but isn't getting grounded. It is probably the switch that is failing to ground the circuit, but it could be that the wire going out to the switch is broken somewhere. The switch is the most likely place for it to be broken. The switches can be repaired. Instructions are elsewhere on my site (starter and turn signal switch repair) and other excellent sites.
3. Test #1 didn't make the starter motor turn? I suggest that one check the starter motor next. Remove the tank to gain access to the starter relay. To check the starter itself, pull the black wire from terminal 87. Jump from that terminal to the positive on the battery. The starter should spin. If not, it's a bad starter or solenoid. The key doesn't have to be "on" for this test.
4. The starter works fine and the only remaining component is the relay. To check the relay, Pull the Brown/Black wire on 31B. Push the key in for power, run a ground to terminal 31B and the starter should spin. If not, you have a bad relay.
All of this assumes a good battery and no broken or altered wires in the system. Wiring colors from a '71 R75/5.
Last edited 2 June 2002. To report errors or ask questions, please email me at email@example.com
Another explanation of our starter
By Brian Mehosky
I thought that I'd try to explain what goes on in our starter,
seems to be some vagueness in some folks' understanding.
The Bosch starter on the /5 has three main functioning parts: a motor, a
gear engaging system, and a high current electrical contactor.
The motor is what spins around and, eventually, causes the engine to turn
over, so that the engine starts up. It's a high current DC electric motor.
The primary failure modes (at least, the ones that occur to me) are (1) dirt
and grime; (2) worn brushes; (3) worn/dirty commutators; and (4) bad/worn
bushings (it has bushings, not bearings). This is standard stuff for DC
The gear engaging system has an electric solenoid (an electrical linear
actuator), a gear assembly that slides on the motor axle to engage and
disengage the gear with the flywheel ring gear, and a lever assembly to
connect the solenoid to gear assembly. [The following is speculation, but I
think it's right] The gear assembly has an override clutch, which permits it
to spin on the shaft after the engine catches, but before the starter is
disengaged. The clutch assembly, like the rest of the mechanical portion of
the starter, can get gooped up with dirt, grime, etc., and will be improved
if cleaned and lubed. [Speculation mode off] Some folks may refer to the
gear engaging system as a "Bendix", which probably sends the folks at
the Bendix Company up the wall.
The solenoid has two functions. The mechanical function is to force the
gear assembly into the flywheel ring gear, and then to permit the gear to
disengage after the engine starts. The solenoid is just a big
electromagnet. When you energize the coil, it pulls an iron core down
(towards the front of the motorcycle, when the starter is mounted). The
iron core is connected to a lever that forces the gear rearward, and into
the ring gear. When electricity is stopped, a spring pulls everything back
into place. The little spade lug on the starter is the electrical
connection to the solenoid coil. (I assume the other side is grounded.)
So, when you jumper that space to the +12V battery terminal, the solenoid
But when the solenoid powers up, it performs its second, *electrical*
function. At the bottom (front, when installed) end of the solenoid is a
hunkering big electrical contactor. So it's also a relay (or electrically
powered switch, if you are unfamiliar with the term). The
contactor/relay/switch makes a connection between the big battery cable
that supplies +12V at massive amps to the starter to the *other* stud on the
solenoid that also has a 13 mm nut on it. That second stud has a big wire
on it, that runs to the starter motor. So another way of looking at the
contactor/relay/switch is as the switch that turns on the electricity to the
starter motor, to make the motor spin.
The *rest* of the "starter circuit" is just switches, relays, wires, and
connections to get 12V to the starter. Those components are, of course,
subject to all the problems 30 year old switches, relays, wires, and
So - to diagnose a faulty starter (*not* a bad battery, or a bad
switch/relay/wire elsewhere in the starter circuit), take off the starter
cover, so that you have access to the starter itself. I've found that the
cover comes off to the *right* much easier than to the left. I only have to
remove the fuel tank and fiddle with the choke and throttle cable to the
right carb a bit - everything else can stay in place. But my toaster may be
If you look at the front end of the starter, you will observe *two*
electrical connections: the aforementioned big battery cable, and a
little wire onto a spade terminal. If you look closely, more inboard,
between the solenoid and the starter motor, you may also see the second
terminal with the second 13 mm nut, and the wire routed into the starter
Disconnect the female connector from the spade lug. You have just
disconnected the entire "starter circuit". But you *still* have +12 V
supplied to the starter by the battery cable.
Connect one end of a jumper wire to the terminal with the battery cable
**BEING VERY CAREFUL NOT TO SHORT YOUR JUMPER TO GROUND**. (I always clamp
the free end to something non-conductive, before connecting the other end to
the terminal.) You would get a very healthy spark if you aren't careful.
Frankly, it shouldn't hurt anything (unless some gasoline lights off), but
it could melt a bit of metal. Alternately, you could run a second wire from
the positive battery terminal - but I think this way is easier.
OK - if you touch the *other* end of the jumper to that spade terminal on
the solenoid, you will (1) energize the solenoid, which will (2) force the
starter gear into the flywheel ring gear, and simultaneously (3) close the
contactor/relay/switch which will (4) power up the starter motor and make it
spin. In other words, you will hotwire the starter, and the starter *should*
work. (If you also had the key in, you could start the motorcycle this way.
If you wanted to *steal* the /5, you could run a jumper from the positive
battery terminal to the left coil - which powers up the *ignition* circuit,
and jump the starter, and ride off. As I'm typing this, I realize that it
would be easier to just kick start it... but I digress.)
If the starter *doesn't* work, you either have (1) a bad battery (very
common), (2) a problem with the battery cable to the starter, (3) a problem
with you battery ground cable (also very common), (4) some kind of loss of
continuity from the ground cable to the starter (unlikely), (5) a faulty
jumper (also unlikely) or (6) a bad starter.
If the starter *does* work when you hotwire it, then your problem is
elsewhere in the starter circuit. Then you get to search for the *bad*
switch/relay/wire/connection - which is its *own* set of issues.
Hopefully, this may provide some insights on how the starter works, and what
to look for when it doesn't. And provide some illumination and instruction
on how to steal your riding buddy's toaster.
My thanks to Brian for his information. I have included it
as an alternative to my rather simple one. Please ask questions or make