Inserting a fuse before the Head Lamp

[REKen]

Hi all,
I blew the lights on my headlamp and my aftermarket tachometer.  I removed the dead light bulb and tested the headlight socket and it still works (so i didn't destroy the ac regulator).  I'm pretty sure it was when I tried kickstarting the bike with the light switch on.  Can I put a fuse somewhere in line to prevent the bulbs from blowing?  Also, the headlight is not wired to be on at all times.  Does anyone know what I need to do to wire it such that it turns on when I turn on the engine and doesn't blow the bulb?

Thanks!
Ken

[mrunderhill1975a]

What year of bike do you have?  And, is it a three-wire or four-wire alternator?

[REKen]

It's a 1987 ex-Indian military bike that was rebuilt.  Based on the schematics, it seems like it's been wired up like an AC/DC ES model (though there is no electric start).  It is a four wire alternator. 

[Scottie J]

This isn't always true, but a fair amount of the of time if your electrical system spikes to where it's blowing bulbs like that, you may have something going on with your rectifier or a short.  You may want to check your electrical system with a multimeter.  With your key turned off, your battery should have between 12.5-12.8 at the terminals.  Next, turn on the lights, you should only have about .5 volt drop.  After you test that, start the bike and see how many volts you have at the terminal, it should read between 13-14.5 volts.  Anything more than that would indicate your rectifier isn't functioning properly and can cause damage to your electrical system.

There's a good chance you don't have any problems,  but you should check just to make sure.

Scottie

[barenekd]

you can install an inline fuse on the wire that runs from the light switch to the dimmer switch. 10A should be adequate
Bare

[AgentX]

He wired your bike AC?  Geez...

Anyhow, concur that there may be a bigger problem that you need to suss out, not just add a fuse to try and make it more bearable.

Are they insisting you have a light that's constant-on to register it or something?  Otherwise, I'd leave it as-is so that you can have the lights off for starting.  And if you do have to make them constantly-on, I'd put a momentary switch in or something so you can temporarily cut the lights for kickstarting...

[barenekd]

Since, if the lights go off, there must be a switch. You can easily bypass that. Just put the two wires in one post.
There's nothing wrong with the idea of having a fuse in the headlight power line. I put one in mine. I had a totally different head light setup, though. Definitely not factory.
As for where the surge would be coming from is difficult to say, but it sounds like the 4 wire alternator isn't quite wired right. I was never very good with the old lighting system that use the key switch as a voltage regulator, but it sounds like that is what you have...partially. Does your bike have a voltage regulator? It probably should have. But not being able to see what's there makes troubleshooting difficult.
Bare

[REKen]

I haven't come across issues registering the bike, and i'm not sure what the law is in MD/VA/DC.  I wanted to wire the headlight to be always on so i can be a fraction more visible to idiot drivers and so i don't need to make the added effort of switching them on/off... it's bad enough when i forget the petcock..  

I have not yet tested the voltage, but i did replace the bulb today.  Even after riding for a little bit with the lights on, the bulb blew out.  I thought about it a bit, and realized that this problem started after I wired the tachometer ground into the headlight ground (amber wire).  Could this be the problem?  Given that the tach is connected to my coil, could power fluctuations entering the tach, blow the headlight? 

[Scottie J]

If the RPM signals coming from your coil to your tach were some how transferring the signal power to the head light, that could definitely be blowing out your bulbs under high RPMs.  I'd rewire your tach to it's own independent circuit with it's own fuse.  I think this might solve your problem.

Scottie

[AgentX]

so i don't need to make the added effort of switching them on/off...

For a dude who spends so much time in the gym, you are one lazy mo-fo...