Headlight / Safety relay barely putting out voltage?

[CoconutPete]

On my 1979 Special, I can't quite figure out the headlight realy. I am trying to trigger it with a 6V power supply, but when I do it, it only sends about half a volt to the blue/black wire for the headlight. If I jump the blue/black to power, headlight function is normal, I just can't get the relay to trigger. Any ideas?

 

[5twins]

Are you testing this still fully hooked up and wired on the bike or removed from the bike? The yellow wire from the alternator simply trips the relay, it doesn't send any voltage through to the blue/black wire. There is a R/Y wire that provides the 12V power feed for the headlight relay. When the relay is tripped by the yellow wire, it connects the R/Y to the blue/black and power can then flow to the light.

If you do still have it mounted, I would check the voltage on that R/Y wire. Maybe it lost power somehow.

 

[angus67]

Why are you using a 6v power supply to test a 12v system?

 

[5twins]

He's just trying to trip the relay and that's what it takes (maybe even a bit less).

 

[CoconutPete]

Everything is hooked up on the bike and the ignition is turned on.

All 3 wires that are a form of red on the harness measure 12V.

I have read that you can fry the relay if you try to trigger it with 12V, so I used a 6V supply I stumbled over. It seems to trip because the voltage on the blue-black to the headlights does change, but it doesn't show 12V, only 0.5 or so.

I'm considering just bypassing the headlight part and just putting in a switch. That's the easy part.

The tricky part is, I'm wondering if you can replicate the starter kill relay with a standard automotive 4-prong one.
(EDIT): The tricky part about this seems to be finding a source of 12V that only runs when the bike is on. I have read all sorts of things about the voltage of the yellow wires from the PMA, but not that they put out 12V!

 

[CoconutPete]

Yep .. the whole thing boils down to this: Is there a source of 12V that only comes on when the bike is running?

 

[CoconutPete]

I'm talking to myself but I think I found an acceptable alternative.

Clutch switch. My bike doesn't have one. I'm not sure if they just weren't around in 79' or if a PO removed it.

I think I'll wire one up and have that take the place of the safety relay.