1981 Rabbit Instrument Panel - Temp gauge/fuel gauge

[dbird]

Hello,

I'm currently working on my MK1 Rabbit, redid the head gasket, currently replacing the clutch. I am waiting for gaskets in the mail right now, but I figured while I waited I could get this figured out.

My water temp gauge and fuel gauge hasn't worked since I got the car, and I figure the temp gauge doesn't work because of this:


It's always been like this, and since most of the car isn't very hillbilly-rigged, I'm not sure if the water temp gauge is wired up to something else instead. There are a few other wires I see on the driver side that I have no clue what they're for:


As far as the fuel gauge, I'm not really sure how that works, like what it's wired to. I can't find any diagrams or descriptions on how the fuel gauge is wired. I think that would help me find out what the problem is. I'm assuming it's a lifter in the fuel sender unit that gives an electronic reading that sends to the instrument panel.

I appreciate your guys' help, and I will be looking into this more when I get the transmission back on and hook up the battery. Thanks!

[ORCoaster]

dbird, let's tackle this one problem at a time shall we?

The temperature sensor is on the flange of the front of the head.  Do you have a multimeter or one that measures resistance?  Put that across the two terminals when it is cold.  What does it read?  Now start the car and let it warm that sensor up a bit.  Measure it again, the value should change.  Likely it goes down. 

Now put that meter on volts and see if you have 12 volts coming to those connections.  Turn the key on to the ignition position.  Do you have 12 volts now? 

Now connect those two terminals to the wires; it doesn't matter if positive is on the right or left.  Does the temperature gauge on the dashboard move at all? 

The gauges on the dash cluster just display whatever voltage they are receiving.  I test them on a bench when I rebuild clusters by just hooking up a nine volt battery to them.  If they are bad, they don't move, and if they are good, the needle sweeps to nearly full. 

On the fuel gauge, again, the float in the tank is a resistor for all intents and purposes.  It will change the value of the voltage going to the gauge when more or less fuel is in the tank.  Most likely, it is a trace on the dash film that is wonky.  Think of very fine wires embedded in a plastic film.  But you can try to figure this out with a meter. 

I owned a Rabbit, and I know that if you pull up the back seat, you will see the fuel gauge on top of the tank.  Clean off the two wires and note their colors.  Maybe brown for ground and a blue and red striped or yellow striped wire for the positive side.  Put the meter on those and see if you have 12 volts with the key in the ignition or run position.

If you don't have voltage there, you should check with the meter if the ground wire gives you a zero reading when putting one lead on the wire and one lead on the metal parts of the car.  9 times out of 10, it is a ground problem with a VW.  Trust me.  Clean up that terminal under the screw that connects it to the body of the car.  Hook it up and turn the key.  Any luck?   

If not, then the wire from the fuse box might be wonky.  This is going to pain your neck and shoulders, and head.  But you will need to get the fuse in the box identified for the fuel gauge.  Do you have a Bentley?  That should tell you which one it is, or you just unscrew the fuse box from its mount and look for the correct colored wire in the back.  Is the fuse good?  Another check to do with the resistance side of the meter.  Touching both sides of the same color-coded wire should result in the meter sweeping to zero or nearly to it.  If you have volts, a good ground, and the wire from the sender to the fuse is good, and you still don't have a gauge that works, you have a problem.

That requires you to pull the cluster and do more testing.  So let's not go into that just yet. 

Do the basic testing first and see what comes of it.  If you still have no luck, I have extra gauges, clusters, and even clusters with a tach in them that I no longer use.  I went all digital on my pickup for a lot of different reasons.  So I can provide you with parts is what I am saying. 

Poke at it some with a meter and let us know the results.  Later man.

[VWSmokr]

In ref. to the OP's 1st pic: have seen those fat temp sensors on some 70s-80s factory A/C Rabbits, Dashers, etc. They were supposedly designed to cut off the air conditioning compressor if the engine's coolant temp rose too high. Definitely not a sensor for your temperature gauge!

[ORCoaster]

Well, it looked a lot like some of the sensors I have in flanges in the spare parts bin.  But if it is as you say, only a cut-off switch, then there has to be something in that same area of the head that is the sensor, right?  Just look around for something with wires on it.  It may only have one wire, as it is grounded in the head for the negative side.

Good that someone is looking at these posts and correcting them. 

[fatmobile]

Yep, that's the cutoff switch for the AC compressor when the temp gets too high.
 The temp switch you are looking for is on the other waterneck coming from the head,
going to the heater.
  The temp and fuel gauges are powered through the voltage regulator on the back of the in the instrument cluster.
When they both are bad, I suspect that.

[ORCoaster]

To replace the Voltage Regulator you have to pull the cluster.  If you do that slap a nine volt battery across the terminals on those gauges and see if they budge  Nuts on the back are all you need to identify.  Behind each gauge, just figure out the - and + on each first.

Oh, and if you need a regulator just ask, I have several I can let go of.

[RabbitJockey]

worth noting, this guy sells new circuit membranes for the back of the instrument cluster. the membrane often fails

[dbird]

Hello, I apologize for the crickets. I'm working on a lot of different things on this car. But  I got the transmission in! Anyway, I wanted to add a little more info on this since I'm almost done.

I did some research into these types of problems, and it does seem like the voltage regulator is usually the culprit. So when I turn the key to "on," the instrument panel is pretty much dead for the most part. None of the indicator lights work, no glow plug, turn signal, nothing. The only light that works is the high beam indicator when I switch the high beams on. I know the speedo worked, not sure about odometer. The greenish-blue light that lights up the face of the instrument panel works fine. Funny thing is, the analog clock actually works, and it works really good. Once I get home I will post some pictures of it. Soon I will take the dash out, but not until I get this damn thing running.




Here is an image of the right side of the instrument cluster, mine has the clock. I posted this image so you guys could see that the temp gauge's needle is really far to the left, almost to where it's hiding beneath the clock's panel. I know, I have yet to test out the temp sensor, which, by the way, I have the one where it's located on the side of the engine head, facing driver's side. It's on the lower part that runs along a coolant hose, but it has two terminals on it. I'm not sure which is which.

Thanks again for the help!

[fatmobile]

 They are both the same sensor.
 So either could be used for the temp gauge or glow plug timer in the relay.

 Do you have any volts on the blue wire to the alternator and is it plugged into the alternator?
 Checking these should help figure out why the alternator light doesn't come on.

[dbird]

Tested some stuff today, here's what I got:

To start off, the battery is very healthy. I first I tested that blue wire going to the alternator. I tested it at the plug where it connects to the alternator. It read 1.33-1.34 volts on the multi.



Here's a picture of the alternator cable I tested. I put the positive end into the plug where the blue arrow is pointing. I noticed there's some weird wiring scheme going on. But that put out about 1.33-1.34 volts.

I also tested the temp sensor terminal, which I did see that you said it could be used for that or as the glow plug light indicator. The end facing the front of the car put out 2.44 volts (key is turned to 'on') and the end facing the back put out 0. I assume this side is the ground. Though there is a blue wire going to it.



I'm not sure how much voltage the sensor should have, but if it's too low, is that a sign that the voltage regulator is faulty? I am already assuming that it is bad, since nothing besides the high beam indicator, clock, and speedo work on the instrument panel. Also, I forgot to mention, I tested the two other plugs for the alternator cable and the read something like 12.30v I believe, I didn't write it down.

Thanks again!

[fatmobile]

That seems low for the blue wire to the alternator. Might should be 10 volts maybe.
 Looks like you need a new plug.
 Try testing the voltage at the twist connector instead of the plug. See if there is more voltage.
 If you ground the blue wire and turn the key, the alternator light should come on.
When connected properly; After it starts and the alternator hits high enough revs to supply it's own 12 volts, the light will go out.
When running; basically the wire has 12 volts at both ends so no current flows through the dash indicator light.

 On the temp sensors both are positive.
 None are ground. The head is ground.
 The way they are tested is to measure resistance across them.
 From connector to ground/head. Without them plugged in.
Somewhere around 47 cold and 270 ohms when hot.
 In the bentley it suggests putting these resistors in place of the sensor and seeing where the gauge sits.
Blue/yellow wire is for the temp gauge.
 With the temp sensor wire unplugged it should be getting about 10 volts from the cluster voltage regulator.
Blue/white is glow plug timer. With it unplugged, glow plugs will always turn on when ignition is turned on, regardless of engine temp.
 
Power to the instrument cluster comes from the black wire.
 It comes directly from the ignition switch, called #15 in the bentley.
 So you can check voltage on the black wire connected to the ignition switch.
With the ignition on.
It's an unfused wire that connects to many things and is hot when ignition is turned on,..  supposed to be equal to battery voltage.
 If glow plugs kick in, battery voltage will be lower.

[ORCoaster]

Nicely done there Fatmobile. That should help him immensely.

[dbird]

Okay, I want to start out by saying thanks to your guys' help, I got the car running very smoothly. Idle isn't too jumpy, almost no white smoke. Rad fan kicks on, everything seems good.

That pretty much makes this issue the only thing keeping the Rabbit from being road-ready for me. Well, technically it's ready now, but I would prefer to at least see what temp it's running at and the fuel it has. I redid all of the shift linkage, and it shifts perfectly now.

Anyway, I did some more of the troubleshooting you guys recommended. I didn't have time to test the alternator wire, though. With the key on, I tested the glow plug indicator light and the temperature sensor wires while disconnected from their terminals. The blue/white wire (on the terminal facing the front of the car) put out around 3-ish volts, and I couldn't get anything at all from the blue/yellow wire. I tried at the connector head, and a bit of exposed wire under it. I could only get 0v from it. I don't really have a sophisticated tool for grounding out that wire, I just cut about 2 feet of wire, held it at the negative battery post and touched the temp sensor wire with it. I had to figure out a way for the wire to hold its position while I checked to see if the gauge moved, and it didn't at all. When I measure resistance across terminals, I did get around 280 ohms hot and in the 40s while cold.

For the fuel gauge, I took out the back seat and checked the plug that plugs in to the fuel sender. The positive wire is a black/violet wire, and the ground is brown. I tested the voltage on the ground wire via the connector, and it read 0. I used the Bentley manual to help me out a little on this. It says to take a wire and pretty much make the ground and positive touch each other with it (while the key is on). I tried it, and it didn't move. But these connectors for the wire are so tiny, I couldn't really get the wire on them. I have a question, is the voltage regulator is bad, would the fuel gauge still work as intended if everything was right with it? Or does that rely on the voltage regulator as well? Also, I'm not really sure where the voltage regulator would be in the instrument panel, if that ended up being the issue. When I look for it on the Internet, I only see results for the voltage regulator on the alternator.

Now, I do want to include that according to the guy I bought this car from, which should be taken with a grain of salt, of course, he told me that the temp and fuel gauge did work, but he "bumped something" and it stopped working. Whatever that means. Right now, the speedo works, the clock works, the illuminating lights work, and the high beam indicator works. Nothing else has any life on the cluster. So I took off the woodgrain panel that holds on the instrument panel and the radio. Had a few laughs of disappointment while doing this. The first thing I noticed is that when I pulled the radio, the antenna cable is already unplugged, way in the back. (Thinking about replacing the radio with an aftermarket, any recommendations?) Anyway, the point of this is when I looked inside, I see a lot of wires back here, kind of dumbfounded as to what they're even for. But there are a few wires that are just completely disconnected, just hanging around. My only thought that doesn't include the previous owner hillbilly-rigging something is that some of these wires that are disconnected might be for gas models or different trims that are just unused. There are also a couple wires twisted together without a cap.

I will upload some pictures later. I also noticed some weird stuff around my fuse panel as well.

Also, fatmobile, when you are referring to the black power wire, do you mean the wire that connects to the top of the fuel injector that looks something like a shutoff solenoid? If so, I got a little less than 12v on that, assuming glow plugs are on.

[fatmobile]

 I think that black wire going to the injection pump is the same as the black wire connected to the instrument cluster.
Sounds like that wire has power.
 On the back of the instrument cluster is where you will find the voltage regulator.
There is a good picture of it in the bentley. It's a 3-legged chip screwed to the surface.
You can follow the traces from the fuel and temp gauges to it.
 If you are looking at the voltage regulator (with the legs pointing down) the left leg is stabilized output, the center leg is ground and the right leg is battery voltage. Check the ground and positive legs first.
 Since there is power to many of the things on the cluster, the regulator or connections to it become more likely as the problem.

[dbird]

Okay, thanks for the info.

I was having an issue yesterday with getting the instrument panel out. I unscrewed the 7mm bolts holding it on, but my dash is the setup where you can't really reach around to the back of the instrument panel to unplug the speedometer cable. So  I unscrewed the speedometer cable from the transmission, and I was able to pull the instrument panel out just a little more, but it's still stuck pretty good in there. I know the method to pulling it out is to tilt it downwards, but I don't even have room to do that. I believe I still need to get that speedometer cable unplugged from the back of it.

For the time being, is there any way I could hook up an aftermarket temp gauge until this is resolved? What's the average temperature this engine runs at?