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Discussion Starter · #1 ·
I start the engine and let it idle but the needle does not give any sign of life. Based on what I read in the Bentley, I shortened the wire against the engine but the needle still does not give a sign of life. Bad wire or connection somewhere?
 

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My gauge never works unless the car is about to over heat then it all of a sudden starts to work. which I guess is better than nothing. does it move a little after you drive it for a while?
 

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Did the connector fall/wire break off the little nail head mate for it?
Mine did and in about 1 min I was back in action.
 

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the side of the engine nearest the radiator(back). its just below the cam cover, very close to your thermostat. it may be well hidden by piping if your car is a turbo.
 

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it's the temp sensor just under the temp housing and the wire connector slips onto it, it looks just like a ROUNDHEAD NAIL , not an oval or a brad or a clout,
 

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That's to turn the fans on

If you touched that end on the block and didn't get anything look at the cluster side.
 

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If you touched that end on the block and didn't get anything look at the cluster side.
thanks a lot! I will check the block side. But I think its the actual gauge in my case. because it will sometimes bounce to where it should be and go back down. I need to put of the temp gauges from my other three clusters in there its just that I need to undo the foil and solder those circuits back on
 

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supremedalek said:
I start the engine and let it idle but the needle does not give any sign of life. Based on what I read in the Bentley, I shortened the wire against the engine but the needle still does not give a sign of life. Bad wire or connection somewhere?
See if you can trace the wire back to the temp gauge using a multimeter and you might find it's broken somewhere. Most likely in the harness near the engine as that's where wiring gets 'cooked'.

It's possible the gauge itself is toast though that would be rare.

Craig.
 

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davidlytle said:
Where is this nail head mate you speak of?
The top of the temp sensor is a single-pin brass contact looking like a nail over which the female spade connector on the end of the temp gauge wire attaches. The sensor screws into the thermostat housing at the front of the cylinder head.

16V engines also have an actual two-pin coolant temp sensor which I believe is used by the ECU and doesn't have anything to do with the temp gauge in the dash.

Craig.
 

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Discussion Starter · #13 ·
For those who are curious, here is the sending unit for the temperature gauge:



c900 said:
See if you can trace the wire back to the temp gauge using a multimeter and you might find it's broken somewhere. Most likely in the harness near the engine as that's where wiring gets 'cooked'.

It's possible the gauge itself is toast though that would be rare.
Now it seems to be working:

Weird if you ask me, as I did not touch anything since I started this thread. I wonder if the the connector at the end of the wire is dirty so it is not making as much contact as it should. Now, if I could also get the fuel gauge and and the odometer to work, and solve my decelerating to stall issue, life would be good. :cheesy:
 

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thanks for the photo now I know where to look. It makes me so mad when it doesnt work. same as the fuel gauge. when I had my radio out i would push on the gauge and it would work then I would let go and it would go back down.
 

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supremedalek said:
For those who are curious, here is the sending unit for the temperature gauge:





Now it seems to be working:

Weird if you ask me, as I did not touch anything since I started this thread. I wonder if the the connector at the end of the wire is dirty so it is not making as much contact as it should. Now, if I could also get the fuel gauge and and the odometer to work, and solve my decelerating to stall issue, life would be good. :cheesy:

Ah well the connection to the temp sensor is in the worst possible spot as oil leakage through the distributor (8V eng. especially) goes straight down on the temp sensor and all over that end of the head. :cool: All my c900's needed to have the spade connector 'squeezed' to make good solid contact. If you do the same, give the connection a clean with a squirt of contact cleaner lube and also the spade lug on the temp gauge wire.

I'm now going off-topic a bit but hopefully the info is helpful... :cool:

1 - As for the non-working fuel gauge, the problem might actually be with the earth or power connections to each part of the gauge cluster. I think, but I'm not exactly sure, that the ground and/or the +12 v power connections to the gauges are supplied through each of the multi-pin connectors at the back of the gauges for the respective set of gauges. And the connections from there to the individual gauges go through the flexible circuit 'backplane'. Maybe some connections are loose.

The other possibility is wiring to the fuel sender - in the early-year classic 900's with the early type of white plastic fuel sender that has 6 male spade lug connectors on the top, when the signal wire to the sender is open-circuit the fuel gauge reads full all the time. In the later year cars with the metal can sender and the 88 or 89 ones with the revised type of white plastic sender, the fuel gauge reads zero when there's no signal from the sender.

Best way to sort it out is take the false floor out of the boot, pull up the rubber boot covering the top of the fuel level sender (small one on RHS - big one on LHS is the cover over the top of the fuel pump) and check the electrical connections to make sure the sender is getting +12 volts and has a good connection to earth, and then check the signal wire output plus see if it's connection is broken or intermittent.

In fact check out the fuel sender end first as that's easier to get at than the back of the gauge cluster.

2 - The odometer problem could be due the internal plastic gears. It's common for the odometer drive gear(s) to crack or have teeth break off as they age, and if they crack right through to the metal shaft each respective gear is attached to, the gear can slip, or even come off the end of the shaft.

Only way to know is to pull the guages out, dismantle them enough to take the speedo head out and then take off it's cover to look at the gears. You need to look at a plastic worm gear that meshes with another plastic gear running at right angles to it. The worm gear normally is fine but the other gear seems to be the one that breaks.

Someone might have a good close-up pic to show these two gears so you can an idea for how they interact inside the speedo.

Craig.
 

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The temperature needle on my 85 c900 jumps right to the H the moment I turn on the ignition and stays there, no matter what. Any idea what this means?
 

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Discussion Starter · #17 ·
Craig, thanks for all the suggestions. As I drove the car last night -- I had gone to a friend's house to air the tires and then had to go to another friend's house to feed their dogs -- I found out neight the left headlight worked under low beam (probably a *** bulb) nor the lights in the instrument cluster would light. It smells like I have some ground issues as you mentioned.

What is the best way to get to the grounds behind the instrument cluster: take the dashboard out (does that require to remove steering wheel?) or the kneepad?
 

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c900 said:
1 - As for the non-working fuel gauge, the problem might actually be with the earth or power connections to each part of the gauge cluster. I think, but I'm not exactly sure, that the ground and/or the +12 v power connections to the gauges are supplied through each of the multi-pin connectors at the back of the gauges for the respective set of gauges. And the connections from there to the individual gauges go through the flexible circuit 'backplane'. Maybe some connections are loose.
Yep, and they're accessible through the speaker hole. Gawd, I love that speaker hole.

There's two multiplugs - one at each end of the cluster - and they're the only connections except the speed sensor's multiplug on the back of the speedo itself. Spray a bit of switch cleaner into the plugs and plug-unplug a couple of times to clean the contacts. That should rule anything out there.
 

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supremedalek said:
Craig, thanks for all the suggestions. As I drove the car last night -- I had gone to a friend's house to air the tires and then had to go to another friend's house to feed their dogs -- I found out neight the left headlight worked under low beam (probably a *** bulb) nor the lights in the instrument cluster would light. It smells like I have some ground issues as you mentioned.

What is the best way to get to the grounds behind the instrument cluster: take the dashboard out (does that require to remove steering wheel?) or the kneepad?
I'd have to check the Bentley manual about the exact location of the ground points in/around the dash. I think there is one down around the ignition switch + transmission shifter assembly, and one behind the main instruments but I think the exact point of attachment to the large cross-member that forms the structural support for the entire dash may have varied from year to year depending how the wiring was being done.

If you want to remove the dash, yes you do need to take out the steering wheel and the lower dash (aka knee bolster, lower valance, etc.) The steering wheel (assuming a non-air bag c900 - did any later c900's have airbags btw?) is held in place with a nylock nut that requires a deep 22 mm socket. Under the nut is a 'belleville' washer (it's formed as a 'wave' shape). The main dash is secured by four screws (one accessible through each speaker hole, and two close to each other just to the left of the middle underside of the main dash. The lower dash is secured with three bolts (one accessible through the ashtray space right in the middle - the ashtray unclips to get it out of the way), and two bolts of which there's one at each end that are accessible from inside each respective front wheel well (one behind the fuse/relay panel, the other near where the vacuum tank lives).

If you have a spare headlight relay I'd give that a try before looking at potential wiring faults to see if the headlight issue is a relay problem or something else. Also check the connector on the back of the headlight switch itself. The wire harness should have just enough slack to get the multi-pin round connector and the switch body out of the dash fascia enough so you can grab both items to seperate them if need be.

Craig.
 
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