The battery gauge in our '72 has, after several years of 'on-and-off' operation, stopped registering battery charge or discharge completely. The needle remains stationary at the 'zero' midpoint of the gauge arc. Before I remove the center gauge cluster to replace the gauge unit itself, I would like to find out if a test can be performed while the gauge is still in the car to confirm that the appropriate electrical signal to actuate the gauge is in fact either present or not. With the passenger side lower instrument panel pad removed, I can access the electrical connection at the back of the gauge unit, and ideally, any test would involve connecting some sort of circuit tester or other measuring device to this connector. However, I don't know what testing tool to use, or how to interpret any results it might display. If a test reveals no signal reaching the gauge, where would the next logical places be to look for a faulty circuit? Thanks for any and all help. Larry Maher
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Re: '72 Battery gauge inop
Some prior threads in the Archieves on this subject.
But, gauge is simple ammeter placed in a SHUNT circuit connection to the battery (otherwise meter would have to carry 100% of car's electrical current and gauge/wiring would approximate that of the battery cable leads). Shunt circuit is constructed by using known lengths of DIFFERENT guage wires to control resistance to/from ammeter guage and these are INSIDE the wiring harness of the car.
Looking at the wiring diagram, you'll find the paths serving the ammeter connect to the starter and the engine electrical B+ supply buss in the engine compartment (read that the outside bar on your horn relay -- Caution! this rail is always HOT regardless of ign switch).
I'd start by looking for the easy/common 'oops' items like flakey connections at horn relay (corroded/oxidized) as well as broken wires at starter solenoid using the wiring diagram's color coding info w.r.t ammeter paths as points of concentration and hope to heck prior owners haven't made too many 'mods' or repairs in these areas.
Then, go to the center console to probe the ammeter itself. Be careful because it's tight in there, especially on A/C equipped Corvettes. What you need is a voltmeter. If ammeter is burned up (not real likely because it's a 'hearty' critter) it'll be an open circuit and you'll see some voltage differential across it IF feed wire paths are intact. If feed paths are open circuit, you'll find NO potential difference across the ammeter.... -
Re: '72 Battery gauge inop
Some prior threads in the Archieves on this subject.
But, gauge is simple ammeter placed in a SHUNT circuit connection to the battery (otherwise meter would have to carry 100% of car's electrical current and gauge/wiring would approximate that of the battery cable leads). Shunt circuit is constructed by using known lengths of DIFFERENT guage wires to control resistance to/from ammeter guage and these are INSIDE the wiring harness of the car.
Looking at the wiring diagram, you'll find the paths serving the ammeter connect to the starter and the engine electrical B+ supply buss in the engine compartment (read that the outside bar on your horn relay -- Caution! this rail is always HOT regardless of ign switch).
I'd start by looking for the easy/common 'oops' items like flakey connections at horn relay (corroded/oxidized) as well as broken wires at starter solenoid using the wiring diagram's color coding info w.r.t ammeter paths as points of concentration and hope to heck prior owners haven't made too many 'mods' or repairs in these areas.
Then, go to the center console to probe the ammeter itself. Be careful because it's tight in there, especially on A/C equipped Corvettes. What you need is a voltmeter. If ammeter is burned up (not real likely because it's a 'hearty' critter) it'll be an open circuit and you'll see some voltage differential across it IF feed wire paths are intact. If feed paths are open circuit, you'll find NO potential difference across the ammeter....Comment
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Re: '72 Battery gauge inop
As Jack mentioned, this item has been discussed before, however, I will give you a brief synopsis on my solution. I am not sure if your 72 is set up like my 66, but I will go on anyhow. My dead ammeter problem was located in the firewall connectors that go to the back of the fuse box. I pulled the two engine wiring harness connectors off of the firewall mounted receiving plugs and noted lots of corrosion there. I cleaned it carefully using a mild acid and lots of water. Then I used a di-electric grease to protect the connectors and re-attached them. No problems now, one year later.
Gary 21316Comment
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Re: '72 Battery gauge inop
As Jack mentioned, this item has been discussed before, however, I will give you a brief synopsis on my solution. I am not sure if your 72 is set up like my 66, but I will go on anyhow. My dead ammeter problem was located in the firewall connectors that go to the back of the fuse box. I pulled the two engine wiring harness connectors off of the firewall mounted receiving plugs and noted lots of corrosion there. I cleaned it carefully using a mild acid and lots of water. Then I used a di-electric grease to protect the connectors and re-attached them. No problems now, one year later.
Gary 21316Comment
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