Electrical Interference

[GlynMeek]

Let me start this off with an apology to the 'purists'...(that I would LOVE to put in tiny font... )

I HAVE A RADIO IN MY COBRA...aaaaaaaaaaaaaaaaaaagh

Now, with that mea culpa out of the way, here's the problem...

When I turn the radio up loud (is there any other way to hear the damn thing...lol), the fuel gauge needle swings across the gauge in beat with the bass of whatever is playing!

The fuel sender doesn't share a common earth with the radio, so I can think of only two reasons (and I have checked both!!!)...

1) Their is induction/interference across the speaker wire and it is close to either the fuel sender wire, OR the fuel gauge ground

or

2) the radio and the fuel gauge share a common ground and I am getting induction/interference this way.

any suggestions, observations or insights would be appreciated

Glyn

[Maurice Johnson]

It sounds like you have identified the most likely causes. Separate the wires and see what happens. Alternatively, you could sell that gauge to someone like Unique Whips for big bucks Does the gauge prefer a particular artist, or type of music. I'm sorry--I apologize

[wtm442]

Originally Posted by GlynMeek

When I turn the radio up loud (is there any other way to hear the damn thing...lol), the fuel guage needle swings across the gauge in beat with the bass of whatever is playing!
Glyn

Cool man! Gotta get me one! Just tell the chicks its a metronome!

[Maurice Johnson]

Imagine a whole dash of these. A Smiths or SW chorus line

[GlynMeek]

rofl...oh yes, VERY helpful suggestions guys...thanks...BUT it is kinda cool to watch



PS Juke Box Hero does REALLY well!!!!

[Rwillia4]

Sound more like they are sharing a common power wire. When the bass hits it sucks up all the available power that can get thru the wire that is causing a drop in voltage that reaches the gauge. Typical stereos have two power wires to hookup: main power and switched power.

The main power wire should go directly to the battery (an always on power source, not to a post that splits the power to many components because it will suck the power available to these components). The main power wire also supplies the radio with a power source when the key is in the off position allowing the radio to retain its memory of settings (yes, your radio will always use some of your battery power so if you are going to store your vehicle for long period take note).

The switched powerwire doesn't typically draw a lot of power its main purpose is to supply voltage only when the key is turned on a good source for this is usually a elec fuel pump (some will say this could possibly blow the pump fuse then the car doesn't work, however the fuel pump draw is continuous and typically not that high..pack a spare fuse in your tool bag).
Ground wire. If you rev your engine and hear a whine thru the speakers that goes up and down with the RPM you picked a bad ground location.
Induction thru the wires, not very likely you're talking about less than 1/2 amp thru any one line to a speaker.

What do you need to do? Change your power source for the radio to the battery, it is usually a yellow wire.

[GlynMeek]

RWillia...thanks SO much for the suggestions and ideas. I will give them a try tomorrow and post the results! I actually have the main power connected to a 'switched' source, so I do indeed lose all the settings every time, but I use it 99% of the time for CD playing, so that doesn't really matter.

Glyn

[Barnsnake]

Glyn,
Does the wire to your fuel sender run near your woofer(s)?
The fuel sender is a variable resistor. If the big magnets in the woofer(s) are inducing a current in the sender lead it might make the gauge twitch.
Temporarily powering the radio from a separate power source (another battery) might help narrow the search.

[GlynMeek]

Jim...how ARE you?

I guess it's a definition of 'near'. The fuel sender wire passes within 4" of one of the speaker magnets. What do you think, 'close' or 'not close'?

Glyn

[Barnsnake]

Hey Glyn. I'm just fine. (My car is all dry and clean again.)

How close is too close? I'm not sure. I've never seen a problem quite like yours.
Are you using a separate amp for the speakers, or is all of the power coming from the radio itself? Is the speaker wire bundled with the sender wire as it goes to the rear of the cockpit? (I'm assuming the speakers are in the rear bulkhead.) You could try running a temporary set of speaker wires "cross country" over the cockpit to the trunk to eliminate the harness induction possibility.

You might try putting a piece of sheet metal between the speaker and the wire as a temporary test. If it eliminates or reduces the needle wag it would confirm induction from the magnet as the culprit.

Keep us posted.