1975 3-1/2 main switch question

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Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

1975 3-1/2 main switch question

Post by Canuck750 »

I have a 1975 3 1/2, all stock, it has signal lights. I am not able to get a spark, the stator ignition coil is new.

I have gone through al the wiring and have replaced most all of it with new factory style crimped terminal connections and new wires matching the colour and gauge of the originals.

I have followed the wire diagram in the owners manual to make sure all of the routing, connections to the fuse block and front frame terminal block are correct, same for headlight, idiot lights headlight / turn switch. I have a new battery, fully charged.

All the lights, horn, turn signals, brake switches work as they should.

I ran a test light to the five terminals on the main key switch, with the key off there is only power to position 1 - red wire direct from battery,
key on 2nd position power to position 2 - Brown and 3 - Grey. Position 4 is Blue - Ground, Position 5 is Green to fuse block shared connections to the two green wires to transducers and stator ignition coil - there is no power at position 5 to green wire in any of the two switch 'ON' positions.

I pulled apart the main key switch and cleaned it all out and reassembled it.

I don't understand what the purpose of the key switch to terminal 5 is, should the green wire power up when the key is in 'ON' positions 1 or 2 ?

I am wondering if I have a bad stator ignition coil or is there a problem at the key switch?
MickeyMoto
Posts: 2415
Joined: 22 Nov 2008 17:41
Location: Even further oop North

Re: 1975 3-1/2 main switch question

Post by MickeyMoto »

With the ignition switch off, the green wire from the switch will 'ground' the stator so that the bike does not start. Switching on the ignition removes the 'ground', there should be zero battery voltage on the green wire.

Disconnect the green wire from the ignition switch at the fuse block and see if you get a spark.

If not, measure the resistance between the green wire from the stator and ground.

Measure the AC voltage between the green wire from the stator and ground when kicking over the bike.

Having two non functioning transducers would be slim, pointing to the magneto coil on the stator.
huub
Posts: 194
Joined: 24 Jul 2006 15:11

Re: 1975 3-1/2 main switch question

Post by huub »

- there is no power at position 5 to green wire in any of the two switch 'ON' positions.

there shouldnt be any power to the green wire in any of the switch positions
people tend to destroy the transducers trying to bring 12 volt to them.
the ignition is self generating , so works completely independant from the 12 volt circuit.
as mickeymoto stated, the switch grounds the stator in the off position.
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 1975 3-1/2 main switch question

Post by Canuck750 »

Thank you for the great information, this makes sense to me now, I knew the ignition is self generating but did not understand the purpose of the green to ground at the switch.

I will check the ignition coil again.

Jim Carey
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 1975 3-1/2 main switch question

Post by Canuck750 »

I went through all he connections once again, green wire from the stator I get 40 AC volts when I kick it over as fast I can, spark was intermittent. I swapped out another ignition pick up I had and the spark improved. After a couple more kicks it fired up. The pick up is the newer black plastic body unit, I can not rotate it as much as I would like to get the timing spot on with a strobe but its close.

Just glad to finally hear it running .
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