ignition off, gen lite on ...

[MZEHNLE122184]

ok, here goes, first post, etc. oh, btw, great forum!!!

Got a 'new' 1984 R100 RT, 56k on the clock (prolly 156k) the other day. First day out, coupla hundred miles, absolutely great!! 2nd day, 40 miles or so on highway, stop for lunch. Turn off ignition: gen lite glows brite red!! Turn Ignition on, but engine still off: gen lite off (oil & neutral lites on). Engine on: gen lite off (at slow idle, whereas it would glow before). Engine off, ignition off: gen lite on, headlite on!! touch front brake, headlite goes off, gen lite still on!!

Took her home, and ran at decent revs (4k), but voltmeter read only 11v or so (whereas it had been reading 12+ before). When home, I noticed battery ground at tranny loose; tightened that, but still same symptoms. There are a plethora of wires added on under the tank and up by the instrument cluster, for aux power supply, heated grips, running lites, etc. Seller told me the diode board has recently been replaced, and the battery seems in great shape.

Can any of you gurus out there point me, preferable easiest stuff first ...

thanks in advance!!

Mark Z

[slow_joe_crow]

FWIW if you have a situation where the gen light is off when the ignition is on and the voltmeter does not show a charge that is typical of an open in the alternator rotor. I believe this can be tested by pulling the brushes away from the slip rings and checking continuity between them. If the rotor is bad Motorrad Elektrik and Eurotech sell an aftermarket rotor for about $100 plus $10-15 for the puller tool. Also check all of the harness connections and relay sockets for corrosion. My 78 occasionally has problems with poor contact at the main relay under the fuel tank.

[bmwmick]

ok, here goes, first post, etc. oh, btw, great forum!!!

Got a 'new' 1984 R100 RT, 56k on the clock (prolly 156k) the other day. First day out, coupla hundred miles, absolutely great!! 2nd day, 40 miles or so on highway, stop for lunch. Turn off ignition: gen lite glows brite red!! Turn Ignition on, but engine still off: gen lite off (oil & neutral lites on). Engine on: gen lite off (at slow idle, whereas it would glow before). Engine off, ignition off: gen lite on, headlite on!! touch front brake, headlite goes off, gen lite still on!!

Took her home, and ran at decent revs (4k), but voltmeter read only 11v or so (whereas it had been reading 12+ before). When home, I noticed battery ground at tranny loose; tightened that, but still same symptoms. There are a plethora of wires added on under the tank and up by the instrument cluster, for aux power supply, heated grips, running lites, etc. Seller told me the diode board has recently been replaced, and the battery seems in great shape.

Can any of you gurus out there point me, preferable easiest stuff first ...

thanks in advance!!

Mark Z

Mark,
This sounds a LOT like a bad switch. The slide rings inside have been known to break loose and make weird connections.

[MZEHNLE122184]

It's been a while since I've visited the forum; thanks for the coupla replies. Here's where I am (and what's been done):
First, I disconnected voltage regulator -- connect battery, gen lite still went on (ignition off in all circumstances); remove ignition switch (vr still disconnected); gen lite on. Ultimately take all relays out of the loop; gen lite still on.
So... had a peek at alternator & diode board. Ground wires (two) from diode board absolutely fried; harness from alternator to diode board worn & corroded; harness from diode board to starter worn & corroded; diode board virtually fell apart upon removal ... ugh!! Old rubber mounts disintegrated (and what fun getting those off [and new ones on, ultimately]).

So, new parts have arrived (new board, 3-wire ground harness, and other elec harnesses, plenty of nuts & wave washers). Mounts have been inserted; harness to starter installed. Just got the harness for alt to db.

Coupla questions for the gurus: The new harnesses are different from the old (prolly original) ones. The one to the starter & accessories used thinner wires. The one from alt to db is just three wires, wrapped, with spade connectors at the end, whereas the old one was three spades at the alternator and a single 'group' of three connectors at the d.b. Do I need to worry about these differences, and on the one from alt to db, is there any order to which color goes where?

And finally: I want to check that the rotors are good. I understand a credit card under the two brushes, then check continuity ... but: am I checking cont. across the two rotors, and if so, what reading? and, do I check cont across the brushes as well?

Also, any other advise is GREATLY appreciated.
Thanks again!!
Mark Z

[bmwmick]

And finally: I want to check that the rotors are good. I understand a credit card under the two brushes, then check continuity ... but: am I checking cont. across the two rotors, and if so, what reading? and, do I check cont across the brushes as well?

Also, any other advise is GREATLY appreciated.
Thanks again!!
Mark Z

Mark,
Here is a good place to start:
http://www.cdegroot.com/cgi-bin/mirr...ricalhints.htm
http://www.cdegroot.com/cgi-bin/mirr...&grdgwires.htm
Its a mirror of Snowbum's site:
http://pweb.jps.net/~snowbum/techind.../techindex.htm
Your rotor should measure between 2 and 3 Ohms on the X1 scale of your OhmMeter.

Do some reading on the above sites and you will learn some diagnostic tricks. One thing to remember, ALWAYS disconnect the battery before pulling or re-installing the front cover!!!!!

[James.A]

I have no experience with "newer" airheads. The VR turns on the light when the battery voltage drops below a per-determined value. It is essential that your battery will hold a charge higher than 13.1 volts. Making sure your battery is fully charged and all connections are good is essential. Pulling the ground cable should make everything go dim. Turning off the key should do the same thing. A light glowing when the key is off would indicate an alternate path to ground. Given my limited knowledge of Bosch electrics, with a good battery, I'd look at the switch and then the voltage regulator. Pull connectors until the light goes out. Front cover safely removed, and the the battery re-connected.