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Old 08-05-2007, 12:16 PM
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Idiot Light to Gauge

'86 El Camino originally had the idiot light dash.

Aprx 3 years ago, I switched to factory gauges from another GM G Body. All the gauges are in one central cluster and the two clusters simply pull out of the dash pod connections. I read on another board that this was a "plug and play" proposition, i.e. pull the lights out and insert the gauges.

Well, it has worked well for all this time. Early last week, however, I noticed the voltmeter wasn't showing the usual charging rate.

I switched alternators, but the alternator did not seem to "energize".

So, I swallowed my pride and delved into the Chevy Service Manual. I found the wiring for the volt gauge and the light are different. If using the gauge, you're supposed to have a resistor wire (10 plus/minus 1 ohm) running from the ignition switch to the bulkhead connector. This resistor wire is mated with a 12 volt wire at the ignition switch.

I ran the wire per the schematic using a piece of resistor wire from an old Chevy ignition harness. Proud of myself, I started the engine and promptly
charred the resistor wire.

Where did I go wrong and what's the solution?

Doc, if you answer this please keep it simple for a small mind.

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Old 08-05-2007, 06:27 PM
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Quote:
Originally Posted by MI2600
'86 El Camino originally had the idiot light dash.

Aprx 3 years ago, I switched to factory gauges from another GM G Body. All the gauges are in one central cluster and the two clusters simply pull out of the dash pod connections. I read on another board that this was a "plug and play" proposition, i.e. pull the lights out and insert the gauges.

Well, it has worked well for all this time. Early last week, however, I noticed the voltmeter wasn't showing the usual charging rate.

I switched alternators, but the alternator did not seem to "energize".

So, I swallowed my pride and delved into the Chevy Service Manual. I found the wiring for the volt gauge and the light are different. If using the gauge, you're supposed to have a resistor wire (10 plus/minus 1 ohm) running from the ignition switch to the bulkhead connector. This resistor wire is mated with a 12 volt wire at the ignition switch.

I ran the wire per the schematic using a piece of resistor wire from an old Chevy ignition harness. Proud of myself, I started the engine and promptly
charred the resistor wire.

Where did I go wrong and what's the solution?

Doc, if you answer this please keep it simple for a small mind.

Doc here,

OK your confusing me here..

ARE you running an AMP gauge or a VOLT gauge???

AN aftermarket Volt Gauge SHOULD be a stand-alone proposition...no extras needed..

An AMP Gauge , on an EC of that Vintage , IIRC, had a remote shunt.. for buss and gauge support..this is what I think you burned out..

IF you used a resistor wire from a Ballast of an ignition system, you were Miles apart in OHMS and light~years apart in Wattage..It's a wonder it didn't burst into flames..

If the manual calls for 10 Ohms +/- 1 ohm..the ballast is 1.5 Ohms..almost a dead short on that circuit..AND the Wattage for a remote shunt would be way up there..as opposed to a ballast , which at best would only be about 5 watts..

If that is the case with yours..two options ...

Toss The AMP gauge and get a true Voltmeter..you need no high current interface, just simple power and ground..a much safer option..

The other, is order the Factory Shunt for the AMP gauge and Install it..and hope you never have future fires..


Doc
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Old 08-05-2007, 11:16 PM
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This is a factory voltmeter. All of the gauges (volt, temp, etc) are in one plastic unit that replaces the idiot light plastic unit in the dash pod.

The voltmeter works. The problem is a power source to energize the alternator.

The schematic shows the volt gauge uses different wiring than the light. Instead of running power from the light to the alternator, they show a 10 ohm wire from a power source on the ignition switch to the bulkhead connector. There, it meets the wire that goes to the field terminal of the alternator.

How do I make a 10 ohm wire? I went to Radio Shack today and ran into a guy apparently dumber than me. All the resistors they had appeared to be for board type assemblies. He also asked about what wattage resistor I needed. I didn't know.

Can these resistors be made to fit into a wire? And, what wattage should I be looking for?
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Old 08-06-2007, 11:20 AM
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This wiring sounds similar to what GM uses to terminal 1 of the 10si and 12si alternators. When there is an alternator light, it is designed so that it will light up if the alternator is not charging, and the light also provides some resistance on that line. When you switch to a voltmeter (no light), you replace the light with a resistor.

Many GM alternator replacement plugs can be purchased with built in resistor. I don't know if AMC has the same option.

Bruce
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Old 08-06-2007, 12:28 PM
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Thanks, Bruce.

I've finally contacted a friend who is into old Chevy trucks. He had some old harnesses that included the correct wire. I spliced it in and it works!
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