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SPDT Electronic Relay Help

john130

Oct 5, 2018
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I have a motorcycle with the Neutral light coming on while in gear and off when not in gear. The transmission neutral sensor is closed when in gear and open when not in gear, resulting in the "N" light coming on and going off and at exactly the wrong time. I tried to wire up a SPDT relay to reverse this, but it didn't work. I have four wires, 2 for the sensor and 2 leading to the "N" light. One of the wires to the N light is energized when the motorcycle is powered. Essentially, all I need is a relay that reverses the transmission sensor. It shouldn't be that hard, but I'm not getting it. Any help would be appreciated.
 

Harald Kapp

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Welcome to EP.

A common type of relay is normally open (n.o.) type, meaning the contacts are open when the coil is noz energized, contacts are closed when the coil is enegized.
This type of relay will not help here as it doesn't reverse the action of the sensor.

You need a normally closed relay (n.c.) (or alternatively a changeover relay (c.o.) where you use the normally closed contact pair).
Feed the coil of this relay with the output from the sensor, Thus the relay will be active when the transmission is in gear (neutral sensor closed) and inactive when the transmission is in neutral (neutral sensor open). The normally closed contact will be open when the relay is active, thus the indicator light controlled by this contact will be off. When the neutral sensor is open (transmission in neutral), the relay will be inactive, the contact will be closed and the neutral indicator will be on.

I wonder why the bike is wired as it is. Maybe the neutral indicator is meant to give an indication aks warning that the transmission is in gear and it is not safe to let go of the clutch?
 

john130

Oct 5, 2018
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Thanks for the quick reply. The bike is a custom 2014 Softail Springer. It wasn't a problem until I moved to Maryland and had to have it reinspected for tags. I was hoping all I had to do is change the "N" to "G" for "in gear", but the inspector won't go for that. I bought a 5 pin SPDT from ebay , I thought either the red and black wire would reverse it, but I guess not. I will look for a NC SPDT.

1pcs DC 12V Car SPDT Automotive Relay 5 Pin 5 Wires w/Harness 30/40 Amp JD1914 #
 

Harald Kapp

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I bought a 5 pin SPDT from ebay
This type of relay is a perfect match for your application. This is what I called a changeover relay.

Connect the coil to pins 85 and 86.
Connect the indicator to pin 87a, this is the normally closed contact.
Connect pin 30 to the battery voltage that will turn on the indicator light, the one with opposite polarity to the other end of the indicator light. This is the same polarity as the output of the sensor.
 

john130

Oct 5, 2018
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Harald, you are very helpful. Sorry I am so dense. When you say "the one with opposite polarity to the other end of the indicator light. This is the same polarity as the output of the sensor". Let make sure I understand. As they are now, the 2 wires from the sensor are either open or closed. There are 2 wires from the light, it appears the black wire is "-" and the green wire is "+" when I check the voltage with my multi meter, red to green and black to black, it reads +12V. When the green and black wires are connected the "N" light illuminates. Attached photo shows my attempt, I did try both 87 and 87a.
 

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john130

Oct 5, 2018
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I got it working thanks for all the help. I had an inline fuse for that it wasn't able to flip the relay.
 
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