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Can anyone tell me where the instrument guages are grounded. Is there only one ground point for the entire cluster or many? Thanks.
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Re: 67 coupe instrument cluster ground.
Rick:
There is a single terminal attached to one of the housing to speedo/tach mount plate hex screws (in the back of the cluster) which is connected to a ground wire in the main dash harness. This serves to ground the entire cluster, which completes the circuit for the lighting, and the internal shunt resistor in the temp. gauge. The fuel and ammeter gauges are not dependent on this ground; the speedo, tach, and oil pressure gauges are, of course, mechanical.
Joe -
Re: 67 coupe instrument cluster ground.
Rick:
There is a single terminal attached to one of the housing to speedo/tach mount plate hex screws (in the back of the cluster) which is connected to a ground wire in the main dash harness. This serves to ground the entire cluster, which completes the circuit for the lighting, and the internal shunt resistor in the temp. gauge. The fuel and ammeter gauges are not dependent on this ground; the speedo, tach, and oil pressure gauges are, of course, mechanical.
JoeComment
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Clarification
Question about instrument panel ground was answered with the following sentence:
"The fuel and ammeter gauges are not dependent on this ground; the speedo, tach, and oil pressure gauges are, of course, mechanical."
I disagree. The mid-year fuel gauge circuit is unique with a Whetstone bridge circuit topology. Earlier and later cars used a simple B+ through guage (a pecially calibrated ammeter), to the tank sender (a variable resistor) to ground. Varying resistance in the tank sender changed branch current making the fuel guage change position. BUT, if B+ changed (generator putting out hard/heavy to recharge the battery after starting; or car stopped at traffic light with turn signals on/foot on the brake and generator below its RPM 'cut through' curve-not charging) current in the branch cicuit also changed making guage pointer position change.
The Whetstone bridge circuit topology made the guage independent of specfic B+ level. Current divided across the individual legs of the Whetstone bridge as a pure PERCENTAGE of total available current based on the position of the tank sender float. This required dealership mechanics be 're-trained' on fuel gauge troubleshooting techniques and the '63 Corvette Shop manual as well as the '66 and '67 Chasis Service manuals devote text specifically to how to troubleshoot this unique fuel guage circuit.
Specifically, they call out different guage symptoms associated with faulty grounding at BOTH the tank sender unit and the instrument panel. For the fuel gauge to function as designed there must be two independent and 'clean' paths to ground (instrument panel and tank sender).
From the '63 Corvette Shop Manual, Section 12-26, Gasoline Gauge:
"Pointer Does Not 'Read' Above 1/2 Position:
Tank guage unit not grounded. Check for proper ground."
and
"Pointer Remains at F Position:
Instrument panel guage not grounded. Check instrument cluster ground-to-harness connector."
So, literature of the period tells us, contrary to what was posted, there is a need for two separate fuel guage ground paths, there will be discrete failure modes/symptoms resulting from improper ground at these two locations, and fuel guage operation IS dependent upon instrument panel ground integrity....Comment
-
Clarification
Question about instrument panel ground was answered with the following sentence:
"The fuel and ammeter gauges are not dependent on this ground; the speedo, tach, and oil pressure gauges are, of course, mechanical."
I disagree. The mid-year fuel gauge circuit is unique with a Whetstone bridge circuit topology. Earlier and later cars used a simple B+ through guage (a pecially calibrated ammeter), to the tank sender (a variable resistor) to ground. Varying resistance in the tank sender changed branch current making the fuel guage change position. BUT, if B+ changed (generator putting out hard/heavy to recharge the battery after starting; or car stopped at traffic light with turn signals on/foot on the brake and generator below its RPM 'cut through' curve-not charging) current in the branch cicuit also changed making guage pointer position change.
The Whetstone bridge circuit topology made the guage independent of specfic B+ level. Current divided across the individual legs of the Whetstone bridge as a pure PERCENTAGE of total available current based on the position of the tank sender float. This required dealership mechanics be 're-trained' on fuel gauge troubleshooting techniques and the '63 Corvette Shop manual as well as the '66 and '67 Chasis Service manuals devote text specifically to how to troubleshoot this unique fuel guage circuit.
Specifically, they call out different guage symptoms associated with faulty grounding at BOTH the tank sender unit and the instrument panel. For the fuel gauge to function as designed there must be two independent and 'clean' paths to ground (instrument panel and tank sender).
From the '63 Corvette Shop Manual, Section 12-26, Gasoline Gauge:
"Pointer Does Not 'Read' Above 1/2 Position:
Tank guage unit not grounded. Check for proper ground."
and
"Pointer Remains at F Position:
Instrument panel guage not grounded. Check instrument cluster ground-to-harness connector."
So, literature of the period tells us, contrary to what was posted, there is a need for two separate fuel guage ground paths, there will be discrete failure modes/symptoms resulting from improper ground at these two locations, and fuel guage operation IS dependent upon instrument panel ground integrity....Comment
Comment