electrical gremlins?

[mike80rabbit]

so iv been workin on my lil sisters rabbit for her gettin all together its a 1980convertible rabbit with 84,xxx miles and thought we were there till she showed me a problem apparently when the car gets hot the tach, the temp gauge, and the gas gauge seem to just drop and dont work.then the battery light comes on and the buzzer starts going off and will shut off when the blinkers are used but returns once they are off the speedometer seems to work fine till around 55-60mph then it starts bouncing around and reads wrong will show 80 when your really going about 65 the car seems fine no stumbling idles no sluggish acceleration everything seems to work except the gauge cluster anybody ever experienced this? am i on the right track lookin at electrical or should i look somewhere else? please help im leaving for school soon and my lil sis needs a good car she can rely on.
thanks,
mike

[CalAltaDubber]

Hi Mike,
First things first.

Welcome to you and your li'l sister.

Sounds like you have a couple of gremlins there, I would say at least two.

The speedo is mechanical, I had the same problem on an '80 Rabbit I used to own. So I think we can rule that part out as an electrical problem.
I can't tell you the exact problem because mine was only a winter beater.

I find it funny the issue only shows up when the car gets hot. So my first question is: When you say hot do you mean normal operating temp. or close to overheat?

Is the heater running? Are the air tubes behind the dashboard all hooked up, or is there hot air blowing on the back of the instrument cluster?

When you use the indicators do the temp and fuel gauges return to normal?

Hopefully we can help you find this, I've not seen this before, but I think we need to define the symptoms a little more so we can figure where to look.

Brian might have a suggestion or two, so keep in touch with us.

[mike80rabbit]

so the temp gauge will work at first and will rise like its gonna over heat but then everything shuts off but the car still runs fine no over heating i thought maybe bad temp sensor but that wouldnt create the other problems.

when the signals are used the gauges stay down (no reading/not working) but at one point i think i saw a slight change when we hit a bump looked like they tried to start working again but then stopped again made me think possible bad ground. but i tried to purposly hit pot holes and bumps and never saw it again.

the heater was running. my sis said the gauges doing what they do scare her so she thought if it was really trying to over heat she would just crank the heat up and try to cool off the motor. and to be honest i dont know for sure if all the hoses are hooked up the heat does blow from the vents and has a pretty strong flow so i would assume they are.
as for the speedo my jeep has similar problems the needle bounces at high speeds but for the most part bounces around the proper speeds not an almost 20mph difference.the reason for my jeeps issue was a speedo cable too long for it so the previouse owner just looped it a couple times under the cab probably binding it just a bit. maybe the same issue for hers?
hopefully this info will help a bit ill be watching for replys and thanks in advance for any info/advise you all can give me

[Briano1234]

Well the answer to your question is easy.

You have a bad 10v voltage stabilizer on the back of your instrument cluster, and a wonky ground.
If the tach, water, fuel gauge and idiot lights are common to the 10v Voltage stabilizer.

You can buy one from autohausaz.com for 15 dollars. or
You can go to mouser.com, and search for a lm7810C.
38 cents

http://www.mouser.com/ProductDetail/Fai ... 52be6WQ%3d

Where is it located?


Then add one piece of electrical tape to the plastic tongue that the main mylar connector is on, "pin" side, this will tighten up your connections.



Lastly splice a ground from the frame behind the cluster to the number 2 pin on the main connector (brown).


One piece of advice, when you have the cluster fascias off, take out the 2 screws that hold the heater controls to the dash. Allow it to float so that when you are shoving your arm
back there to disconnect the speed, you won't break the mounting tabs.

[CalAltaDubber]

Why did I know you would have the answer Brian?

[mike80rabbit]

sweet thank you got some work to do now and really thanks for the speed of the answers i leave saturday night for school so i should definately have time to fix this thanks again ill let you all know if theres anything else i find