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GMR 04-05-2011 06:03 PM

protecting a gauge
I want to protect whats called the "battery gauge" on a '64 vette. Here's the layout.

Wire from Alt Bat terminal goes to horn relay. The horn relay terminal has 3 wires all spliced together in same connector. BLk/wht goes to "battery gauge", red (red-1 say) goes to big terminal on starter solenoid, another red (red-2 say) goes to a junction of red wires which feed the ign sw bat term, fuse panel, several accesories. Back at the starter solenoid, the red-1 is spliced into same connector as a black wire. This black wire goes to other side of "battery gauge".

So I want to protect this "battery gauge". Not sure where to install fusible links and/or any inline fuses, and what gauge of fuse if required. I know the fusible links should be 2 wire gauges smaller (12ga requires 16ga fl).

crownver 04-05-2011 11:37 PM

If you want to fuse it it'll have to be a big fuse. At least the max amps of the alternator. All the charge from the alternator to the battery goes through the guage. I would think you'd want the fuse on the alternator side of the ammeter. If a wire shorts there you would have full power from the battery going through the gauge to ground, if it shorts on the other side you'd have the alternator power going through it, which it's rated for.

cobalt327 04-06-2011 02:31 AM

I believe your "Battery Gauge" is basically a galvanometer. As such it isn't 'actively' connected to the vehicle battery current, so really shouldn't need any protection per se.

75gmck25 04-06-2011 04:31 AM

I'd have to diagram it out to be sure, but it sounds like you have an ammeter gauge that uses a shunt. If that is the case, it is not a full current ammeter. Its just measuring the voltage difference between two points in the harness and calculating amperage.

My '75 GMC has a gauge wired like this, and it just uses a five amp fuse in each wire that connects to the gauge. They are inline fuses that are in the wire lines under the hood. The actual amperage flow to the gauge when you use a shunt is quite low.


GMR 04-06-2011 05:23 PM

1 Attachment(s)
Thanks fellas.

Here's a diagram. Could you please give me your recommendations on where to put fusible links/fuses/circuit breakers.

Hope you can read it.

The Red-2, Blk/Wht, and Red-3 share a ring terminal at the horn relay.
The Red-3 and Blk share a ring terminal at the starter solenoid.

I'm guessing I should separate and put fusible links on Red-2 at the starter solenoid and Red-3 at the horn relay. Probably, to be safe, I'll put the inline fuses on the Blk and BLk/Wht wires to the battery gauge as mentioned. Looks to me the cig lighter is unprotected or will a fusible link at Red-3 do the job?

Would you ever use a fuse and a fusible link on same circuit?

daveismissing 04-09-2011 07:55 PM

Unless I'm missing something ( a bit fuzzy) the way you've drawn it the gauge is shorted by a red wire?. Don't see how that works.

GMR 04-09-2011 09:01 PM

Not sure what you mean. The 2 wires to the battery gauge are a BLK from starter solenoid and Blk/Wht from horn relay. I'll try a more clear diagram.

daveismissing 04-09-2011 10:08 PM

Where you have 3 wires going into a "box" if they are attaching to separate distinct terminals on the "box" maybe you can show that.

vicrod 04-10-2011 02:25 PM

The battery meter is an ammeter. It will have a 0 amps centered position and + amps and - amps positions.
An indication in the + side of the ammeter shows if current is flowing from the alternator to the battery.
An indication in the - shows excess current flowing from the battery to the accessories or the alternator is not working.

The ammeter measures voltage drop across a shunt. In this case the shunt is the heavy red wire connecting the battery to the alternator and accessories.
The smaller black and blk/wt wires go to the ammeter. If they are not fused they should be.
Inline fuses (4 amp) should be installed in each of these wires at a point as close as possible where it connects to the heavy red wire.


daveismissing 04-10-2011 06:40 PM

If its a typical meter movement then the flow would be milliamps? I would postulate 4A may protect the attaching wires but protecting the movement may require something very small, say under 1A?
If its configured differently I'd enjoyed being enlightened.
(not intended as a bad electrical pun)

GMR 04-12-2011 08:13 AM

1 Attachment(s)
Hope this is a more readable.

I plan to install inline fuses on the battery gauge wires, as suggested, after things are worked out - thanks.

The red and blk wires at the sol share a spade connector. The two reds and the blk/wht share a connector at the horn relay. The horn relay has 2 terminals but they are on the same bus bar.

vicrod 04-12-2011 02:42 PM

I suggested 4 amp fuses only because the GM schematics show them.


malc 04-12-2011 02:50 PM

If it is an ammeter, read this.

vicrod 04-12-2011 03:09 PM

The article supports my position that the meter shunt in GM alternator equipped cars is the main accessory wire which is part the main harness and does NOT pass into the passenger compartment and through the ammeter.
Any vehicle that has the shunt as part of the ammeter can be hazardous as mentioned in the article.


GMR 04-13-2011 08:54 PM

Good article malc, thanks.

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