GPS blows fuse when starting engine

[jkboiler]

I have a Garmin Nuvi connected to a switched power line on the anti-left plug in the relay box under the tank.  It works fine when I turn the key.  It then gets power, the GPS boots up and all is well.  But when I start the engine, it blows the 1 amp in-line fuse that I have in the 24 gauge wire that powers the GPS.  Any ideas why this would happen?  Should I use the accessory plug instead?

I've read that some use the hot side of the starter relay.  They indicate that this is switched power, but on my bike the power lead to the starter relay has power all the time (is unswitched).

1994 K75

[kioolt]

My first thought is that when you go to start the bike that the battery in the Nuvi is feeding power back though the 1 amp fuse to do that.  I would think that others would be having the same problem on all brands of bikes and cars if that were true.  But who knows, maybe your Nuvi have something wrong with it. You could try putting a diode inline with the fuse that would block this backfeed.  A 1N4000 series diode would do the trick and can be bought at Radio Shack for practically nothing.

[Scott_]

Does the fuse blow if you start the bike before you turn on the gps?

[rbm]

As kioolt said, it's probably the back EMF created by the GPS causing current spikes that is blowing the 1A fuse.  Also, 24 GA is very small for power distribution.  I think you should beef up the wire size to 18GA or 16GA and use a larger fuse, possibly 3A.  Afterall the fuse protects the wire, not the load; so size the fuse appropriately.  16GA wire can withstand 22A maximum and 24GA can only withstand 3A maximum.

[jkboiler]

Thanks, that is some good info.  But after sleeping on it, I think I know what I did wrong.  I grounded it to the "ground" side of the starter relay.  I don't think that is a true ground, but only acts like one until the starter it activated.  It then becomes the "hot" wire that powers the starter motor.  Basically, I've got it grounded through the starter motor, until the starter relay switches on, then its "grounded" to a hot wire and the fuse blows.  Probably lucky it didn't fry my GPS with it wired this way.

Over the weekend I'll ground it straight to the frame like I should have before, and see if that solves the problem.

[mystic red]

There is a ground stud under the tank, at least on the 1100's...

[kioolt]

The starter terminal should NEVER be used for a ground.  It is not a true ground in any sense.  It is actually about 2-3 ohms (a guess, since I have never measured it) above ground at best and then only when the starter is not hot.

[jkboiler]

Thanks kioolt . . . I see now that you are absolutely correct.  I ran the ground wire to the frame and all works well.  I should have realized that and must have had a brain dead moment when I "grounded" it to the "black side" of the starter relay.  I think I'll blame it on the Florida heat, which means I was doing the wiring at night when the temperature is more tolerable in my garage.  I think my brain must have already shut down the for evening.