GOT IT !!! Brad, Caddman, somebody........

[Top Cat]

I posted this in the off topic forum but I'm getting impatient, no one answered me there :-/
I am trying to install a tach on Cindy's 750 Shadow C2.
I followed the directions that came with it but it will not Show RPM's
When I turn on the key it lights up and the needle goes all the way to max then drops back to zero. So I know I have power and ground correct. When I start the bike the needle doesen't move at all. Any one have any ideas?
I have checked on Honda boards till I'm blue in the face.
PS When I check the posts on the coil I get a positive reading when the key is on and also when the bike is running. So I hooked the wire to the black post.
Come on you guys, help me out here :'(

[macmac]

I am not familar with the bike, or this tach, but there needs to be power in with the key, ground and the (-) side of the primary wire to the coil to read the pluse on most tachs..

Primary wires are thin, the 2ndary side is the plug wire. It may be you need some form of adapter, but i don't know what to tell you on this one.

[cactusjack]

I've never installed a tach on a bike. Sorry. What macmac said is correct about the connections. I've installed a few automotive tachs in my day, well many years ago.

[macmac]

If I could just friggin spell... pluse should be pulse.. negitive should look like (-)....

[nomad]

some tachs have a little adjuster on the back indicating how many cylinders the engine is. just a guess here...is it set right?

[scion0]

Trip has a tach on his Nomad, I believe.

http://www.shadowaero750.com/mods.aspx

13th one down under Custom Modifications... hope it helps. :)

[Top Cat]

Thanks for the replies guys. I am going to move the wire going to the coil to the other post tomorrow. If that doesn't do it then I am at a lose. Will take it to the dealer :(

[VulcanE]

TC, I copied this off another honda web site, might be some help,

There are 4 wires running from the tach:
Green - goes to the pulse side of the igniton coil (green coloured connector on
the coil)
Red - to switched on power
Yellow - to lighting circuit
Black - to ground

When I wired my Tach up, I just connected the red and yellow together on the same "switched circuit". What I think you need to check, is to see if you wired the green wire of the tach, to the side of the coil that has a green wire.

[Top Cat]

Thanks for all the replys guys.
The instructions said nothing about green side of coil. I moved the connector to that side as VulcanE suggested. Bingo, it works.
The instructions said negative side, as there was a positive reading on both sides I assumed that black would be the negative side :-/

I didn't reply before because I had no idea what colors the wires on your bike were.

This is the confusing thing about coils:
A bike runs on DC. A coil is a transformer, and transformers only work on AC. In AC there really is no positive and negative. How they make a transformer work on DC is to switch the DC on and off real fast. In the case of a bike, they switch it every time you want a spark. That "switching" is what the tach reads to determine RPM.

On a bike, the "negative" side of the coil is the wire running through the kill switch to the ground, so the juice flows from the computer (which switches or "pulses" it on and off) through the small coil windings, to the kill switch, to the ground. It's all one wire, so it all reads positive, until it starts pulsing.

Now DC current goes right through a coil of wire with no problem, but AC or pulsed current is reluctant to do so (in fact, coils are said to have "reluctance" ;) ) AC makes that coil an electromagnet, and the magnetic field holds the current creating the magnetism back like a dam.

So where does it go? Well the field isn't really like a dam. It's like a bridge and it bridges the current to the fat windings of the coil which fire the plugs. the fat windings are few, and have very little reluctance, so the voltage shoots through them like crazy, going from zero as the pulse starts up to 30,000 volts or more to run the plugs. (In the old days it was 10,000 volts, but it's steadily risen over the years, and I think some modern vehicles may make as much as 50,000 or 60,000 volts.)

Whew! That was long!

Anyhow, while I couldn't tell you what color your wire was, I hope you understand now why they were both reading positive.

[VulcanE]

TC, Glad all is good for ya ;)