1973 R75/5 - electrical issues?

[Kidasters]

Hey guys -

I've been working on a light restoration of my 1973 R75/5 that I purchased in April. I put the battery in today and got it connected and secured. But, something is wrong. With the key in - I have lights - low and high beam. But, that's it. No turn signals, no horn and I can't get the starter to roll the engine. I did change all the plug wires when it was apart, but I'm sure I have the plug wires on correctly. The ground is on and secure, and there are two contacts on the positive side of the battery that are also secure. Thoughts?

I'm stumped.

[willstone]

Is the green neutral light showing?

[Kidasters]

Yes it is.

[schrader7032]

What about the kill switch? I forget what that does...not sure if it cuts all power or only to critical systems.

Beyond that, I'd be looking at the starter relay for potential corrosion on the terminals.

Curious...what are the two contacts you mention on the positive side of the battery?

[Kidasters]

There is no "kill switch" on the 73. You pull the key out.

I do wonder if it's the switches though. I'm going to replace both. We'll see if that helps.

[srankin]

Isn't the nail style "key" ignition switch on the /5 bikes prone to problems like this? Are there fuses or is this an early year bike without? St.

[Kidasters]

Yep - it's got the "nail" key. I was in the bucket last night, and I didn't see a fuse on it. I'll be poking around more though.

[Darryl.Richman]

Not sure if you have this, but attached is the wiring diagram.

If I understand right, that you have lights, but no start, then it looks to me like the switch the "nail" pushes on is not making contact to allow power to the rest of the system. Look at the 30/51 (power) terminal on the circuit board and the switch between that and 31 (ground). If the key doesn't make that switch actually contact 30/51, then there's no power to the horn or the starter button.

(I snipped the wiring diagram from the /5 workshop manual in the BMW Models info in the website's Knowledge Base.)

[cbclemmens]

The R 75/5 has 2 fuses in the headlight bucket, 1 is on the accessory side and the other is on the ignition side. They are pointy on both ends and are held by clips on the circuit right behind the headlight plug. The starter relay is unfused and its power comes from pin 30 on the ignition switch. The headlight power comes through the accessory fuse. The power for the coils is also unfused and comes off pin 15 on the ignition switch (solid green wire). Pin 15 on the ignition switch also feeds a solid green wire to one of the fuses. Also the R 75/5 does not have a neutral lock out. The starter will engage even when the bike is in gear, so you don't need to bark up that tree.

I would start with the ignition switch. It sounds as though power is not getting to pins 15 and 30. You might just need to clean it.

Craig

[Kidasters]

Super helpful. Thank you. With the headlight off, it looked like the nail was getting to the bottom of the hole, but maybe I need to take some stuff apart and clean it up more.