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temp, and battery gauge

 
machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 04/25/11 11:28 PM

I replaced the console and center instrument cluster bezel on my 1979 Corvette  because it was showing some wear and tear . All gauges worked except the clock before the install.I also replaced the printed circuit gauge cluster and a new quartz clock kit. The replacement went well, except the battery and temp gauge don't function. All the  bulbs and other gauges work including the clock  so Iam thinking  the plug socket should be good. All electric funtions  work on the car
right down to the glove box light. So what gives?? I did do a complete spark plug and plug wire upgrade and new alternator connections , everything looks good and the alternator is charging the battery . I did notice the wire for temp sending unit was off probally from the spark plug change I fixed that . Iam not sure what to do I just hope I don't have to remove that pain in the ass bezel'  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 04/26/11 06:51 AM

the quick test for the temp gauge.. is to turn the key on...  Engine off..   pull the green wire off the temp sending unit on the motor...  the gauge should swing all the way one way.. probably to the cold side...    now.. touch it to ground.. the gauge should swing all the way hot...... this tests the gauge and its circuit...

if the gauge does not move...    time to access the gauges again.. sorry...

do you have an OHM meter????

key off...    look at the printed circuit...  or if you have the old printed circuit.. scan it... print a paper copy... or digitally draw the effected circuits with color..

this will allow you to verify that the printed circuit is properly attached to the gauge....      and that when you plug in the harness connector that it is fully seated and contacting...   you might want to think about shining up the contacts on the wiring harness connector...

i will have to search around for a printed circuit diagram.. i don't have one for that year handy...  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 04/26/11 08:59 AM

thanks for the good ideas, the printed circuit is brand
new. I just did your gauge check and it dosn't move at all, the gauge reads hot  and there is power to the sending wire. During the install when I first connected the wiring harness to  the gauge cluster there was some movement and then the  gauge stayed  to the hot side . My Battery gauge did nothing . Looks like I will be shining up  the contacts for
starters when I get time. I just spent a week off work for the cluster , console , hot coil , plugs , wires, braided lines and lots of chrome. GM sure did a low quality job on the console and gauge cluster. The printed circuit is really cheaply made. Again thanks for the pro tips.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 04/26/11 07:27 PM

question.... does it stay hot all the time...

that might show that the green wire to the engine is shorted to ground someplace..

when i was back in auto shop.. one of the parts guys had an mid 60s chevy..  when you tried to turn the key on.. the gauges would all peg and the battery cable would move..  it would change shape... turned out he had gotten the green temp sending unit wire under the valve cover...  it had taken all the current the circuit could supply...

i worry that you have some kind of short to ground on the green wire to the engine.. even if its where the cluster plug shoves into the printed circuit ... as that has to be centered....

if you drive the car or even run it with the gauge pegged like that.. you take a chance of it burning out...  so be prepared..

you might really want to verify that the printed circuit where it is bent to allow the plug is actually properly centered.. or that the plug is properly installed.. strange things have happened...  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 04/26/11 11:13 PM

Yes it does stay hot all the time , with the ignition on or off ,its 3/4 pegged , the battery gauge also dosn't work it reads zero. All the bulbs work in the  cluster including  the temp and battery, does that still mean the socket is not centered ?? I did try several attempts installing the plug. Maybe this is a shop issue.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 04/27/11 07:06 AM

something is wrong....    you did the work... its not that hard... and will the mechanic use as much care as you have done....

to make things perfect... sometimes you have to take them apart several times...

there is a big repair area at the end of every automotive assembly line.. where cars that have problems are driven for final repairs..

do you have an OHM meter?????  digital volt meters start at 7 bucks..  you don't really need to spend over about 30 for a good one...

when the cluster is out....

ohm the sensor at the engine ... between the sensor connector and the engine.. write that number down...

then check the wire at the cluster connector... to ground.. with the sensor at the engine disconnected...  should read OL...  open lead...  hook the sensor up and the engine...    should read really close to what you measured...  within a ohm or two of what you read directly... closer would be better..

but you say the gauge is stuck at 3/4...  thats NOT pegged...  pegged is where the gauge is all the way over...

you have either no power to the gauge or no ground..

since the other gauges are working.. i would say ... i wish i could find the diagram of the gauge cluster...  as i know how to read those...  

you need to ohm the printed circuits connections to the gauge..  

verify the proper voltage is on the wiring harness..

if you still have the old printed circuit... scan it and do several copies.. trace the circuits out with a highlighter marker...  this will make it much easier to figure out where the powers and grounds all ***

be back with more info...  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 04/27/11 07:48 AM

i still cannot find the circuit diagram for the 79... i did find one for a 77.. but that looks different than your description...

don't Forget ... looking at this section of the diagram..  you are looking at PROBABLY the end of the plug...  

pink and black is power..
Pink is the fuel sending unit
a wire to a ground connection.. be sure to check this with an ohm meter,
Brown to the side of the alternator terminal 1.
Tan is the oil pressure circuit.


ground wire...  be sure to check this with an ohm meter to ground...
Dark Green to Temp Sender

yellow to seat buzzer,
blank
blank
orange to dome light circuit.. powers clock...

79Corvetteconsoleprintedcircuitconnector2


remember... this is looking at the END of the connector.. not the back...  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 04/27/11 10:10 AM

Looks like the cluster is coming out, Hey its not the only upgrade I have done twice. No power or ground makes
sence to those two gauges. I will buy a new ohm meter and check the connections . I just wish I had more free time. Thanks for the great help I will let know how things go.  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 06/15/11 04:40 PM

I pulled the cluster out I have power to all the gauges including the 2 that don't work, temp and battery
So does that mean its a ground problem??  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 06/15/11 04:41 PM

I pulled the cluster out I have power to all the gauges including the 2 that don't work, temp and generator
So does that mean its a ground problem??  I did notice someting odd which is the generator light works but the gauage dosn't . I spun the alternator belt off the pully racing the car alittle  and the generator light came on so I know the gen light works ok.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/15/11 06:34 PM

did you print out the image above....

and verify the powers and the grounds...

and the continuity of the wires from the temp sending unit for the temp gauge...


and from the side plug on the alternator..  the larger of the wires... as i recall..

gauges do burn out..

where you able to OHM the new printed circuit board you installed to verify the continuity between where the gauge hooks up and the  connector plugs in...

i have had terrible problems on other printed circuits that were installed slightly crooked...

can you lay the old printed circuit on the flat bed scanner... to scan it...

then draw in the circuits you need to test...  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 06/15/11 07:49 PM

all I did was ohm the printed circuit board to all the gauges and there is power. Temp sending unit wire and side alternator plug have power. The Generator light works and functions properly.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/16/11 06:21 AM

there are 3 connections to the temp gauge...

one has power...

one has ground..

the green wire is also a variable ground

with the printed circuit plug removed from the circuit board... there should NOT be power on the green wire..  it should have some resistance as its hooked to the temp sender on the engine..

just because you find power on a wire .. does not mean its the proper to operate the gauge...

this is for a slightly newer camaro...


: Coolant Temperature Gage Test

Disconnect the Coolant Temperature Sender connector and place the Ignition Switch in RUN.

If the Coolant Temperature Gage reads cold, go to the next step.

If the Coolant Temperature Gage does not read cold, check BLK (150) wire at terminal of Instrument Cluster Printed Circuit connector C2 for an open (this is the black wire coming off of the black connector for the PCB at terminal 9) and DK GRN (35) wire and terminal G1 of Ignition Switch connector C1 (this is the dark green wire coming off of the black ignition switch connector) for a short to ground. Repair/replace as necessary.

Turn Ignition Switch to BULB TEST.

If the Coolant Temperature Gage reads hot, go to the next step.

If the Coolant Temperature Gage does not read hot, check DK GRN (35) wire for an open (see schematic) (you want to check it for an open between the ignition switch and the coolant temperature gauge. Not sure which location it runs to.). Replace Ignition Switch if wire is OK.

Ground DK GRN wire at Coolant Temperature Sender Connector.

If Coolant Temperature Gage reads hot, replace the Coolant Temperature Sender.

If the Coolant Temperature Gage does not read hot, check DK GRN (35) wire for an open. Replace the Coolant Temperature Gage if wire is OK.

Coolant Temperature Gage
The Coolant Temperature Gage is also operatied by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender. This has 55 ohms resistance at 260* F (hot coolant) and its resistance increases at lower temperatures. Resistance is approximately 1400 ohms at 100* F. This causes the current flow through the sender and one coil to increase as the coolant temperature increases. This moves the pointer.
 

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 06/16/11 07:25 PM

why would the generator light function properly and the new gauge not work  

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machine350
I love my Chevy Chevette!
Posts: 21
Joined: 04/11
Posted: 06/16/11 07:55 PM

could I do a bench test with the gauge removed from the cluster.  

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