'86 DL 240 wagon

There are a few wires on this Volvo that have all the insulation either burned off from shorting or which have disintegrated - as I understand that for this car the insulation was biodegradable . . .

One of these naked wires is the wire that goes from the temperature sensor on the block to the instrument panel. With this naked wire connected and the car running, the gauge shows all kinds of different temperatures from over heating to nothing. I installed a new sensor and the same thing kept happening.
I was going to just replace the entire unit with a package that had the sensor and a new meter I would mount on the dash. But then I thought that maybe both the meter and the sensor are ok and it's just that the naked wire is shorting out as it moves around with the wind - touching metal. So I connected a wire to the sensor and then to the meter on the back of the instrument panel.
The thing is - there are two wires that connect to the back of the guage; an orange one and a blue w/white stripe? one. I connected the sensor wire to one of the two sided connector at the panel - and connected first nothing, then in turn, each of the two wires. Nothing happened. No signal.
I did use the entire spool of wire - 30 feet - too long? Signal too weak?

I am guessing that one of the wires supplies juice and the other goes to the sensor. The meter is showing resistance based on the temperature of the oil?

No I haven't tested one of the wires to see if it's hot. and too I should try just wrapping the naked wire until it disappears into the harness.

But why would connecting the good sensor to the gauge - along with the other wire not show movement?

Thanks.

 

Certainly the "naked" wire running from the sensor to your instrument cluster is most likely the cause of your temp gauge issue. However, I'm having trouble understanding the wiring you describe. I have had several clusters apart from late model 240s and none have wires that go directly to the temp gauge. Do you have a temp gauge that is external to the instrument cluster?

According to my Haynes manual wiring diagram, the temp gauge in the instrument cluster has two inputs: 1 input provides 10v from a voltage regulator on the cluster circuit board. The second input comes in from the sensor on the engine. It should be a yellow wire.

 

there's two temp sensors on the engine. one has two pins, and goes to the ECU and ICU and is used by injection and ignition. the other has 1 wire (Yellow, as act1292 says), and is used just by the coolant temp gauge in the instrument cluster. This yellow wire goes to the full circle connector 31 pin 2

the connectors to the actual gauges are not visible on the back of the instrument panel, they are all internal circuit board connections.



(swiped forum pic). the black thing on the back of the panel on the right of this pic is the tachometer (unless you have a clock there).

 

Blindly applying voltage or ground to unknown terminals is how things get fried.

The dual terminal connection at back of cluster is the speedo output. Sounds like thats what you mentioned. Dont apply 12v there! (to the top left of white speedo housing in pic above)

If you really need to bypass the cabin and engine wiring to rig your temp sensor. You need a multimeter and a wiring diagram.

The temp sensor wire is a single wire that goes into the semi circle plug, possibly the full circle plug. I forget. Look it up.

To test your wiring, you ground out the wire at sensor and temp guage should go to full hot. If not, you have wiring issues, or temp compensation board issues. My guage is acting up ever since I put a used cluster in with a temp board I had removed. The pins lose tension I have heard. I have problems with guage reading too cold most of the time. I can get guage to read differently with the good ol' acoustic tuning method (smacking the **** out of the dash)!

I have a couple extra temp comp. boards on the shelf I can install if I really need to. IPD also sells a single wire for $15 if you want to go that route to bypass the comp board.

 

REPLY; I have two sensors that look like temp sensors. they are about six inches apart on the intake manifold side of the engine. The higher one has the naked wire. If I connect the naked wire to this upper sensor, I get wild readings on the gauge. If I disconnect that wire, I got no reading. On the instrument panel, there is a two pronged connector (same circuit) directly behind the temp gauge. If I disconnect these two wires, I get no reading on the gauge - so I assume one of those connectors is to the temp gauge with the naked wire. In another post, someone tells me the other sensor "goes to the ECU and ICU and is used by injection and ignition". If the naked wire line is replaced with an insulated wire directly connecting the sensor and the gauge - AND either of the other two wires that were on the two pronged connector - nothing happens.

People are telling me there are no visible connections from the sensor to the instrument board - yet I have the above experience. Thanks

 

I have two sensors that look like temp sensors. they are about six inches apart on the intake manifold side of the engine. The higher one has the naked wire. If I connect the naked wire to this upper sensor, I get wild readings on the gauge. If I disconnect that wire, I got no reading. On the instrument panel, there is a two pronged connector (same circuit) directly behind the temp gauge. If I disconnect these two wires, I get no reading on the gauge - so I assume one of those connectors is to the temp gauge with the naked wire. In another post, someone tells me the other sensor "goes to the ECU and ICU and is used by injection and ignition". If the naked wire line is replaced with an insulated wire directly connecting the sensor and the gauge - AND either of the other two wires that were on the two pronged connector - nothing happens.

You mention 'connector 31 pin 2 - a yellow wire. Should I try and run a fresh wire from that pin to the sensor?

 

Pierce tells me that the right connection is connector 31 pin 2 - a yellow wire. Should I try and run a fresh wire from there to the new sensor? Thanks

 

thats what I would do, if the wire is crunchy. you could unplug 31 (the full circle connector), and measure the resistance of harness pin 2 to ground, that would be the full path to the sensor.... I believe that resistance is inverse to the temp... hot == low resistance, cold == high resistance.

be sure to use auto grade or better wiring, which is oil/fuel and temp resistant. the best stuff is aircraft wire but its hard to find and expensive.

 

You should ignore us folk on the internet telling you which wire does what, and do tests with a multimeter to trace out the circuit.

 

In the picture that Pierce posted, you can see 4 nuts on the back of the instrument cluster circuit board. These 4 nuts are the actual terminals of the fuel gauge and temp gauge (each gauge has two terminals). Follow the traces on the circuit board from the temp gauge nuts to see where they run. One should run to a voltage regulator (a chip on the circuit board) while the other should run to a prong on one of the two round connector. Identify the pin on the connector and the wire associated to that pin on the wiring harness. According to the wiring diagram, this wire should be yellow. If you are running a new wire, it should run from the temp sensor on the block (the one with a single wire) to the prong on the connector you have traced.

Note: If other wires in the engine compartment are "naked" as well, you may want to consider a replacement wiring harness as you will have other more serious problems.

 

I connected pin 2 to the new sensor. For a couple days the reading was just below the dot - the middle of the gauge. Then the reading shifted to be right on the dot. But on the way over here to Starbucks on the freeway just now, the indicator stayed at zero too long before again centering on the dot.
Do you know how I could simulate overheating so as to get a reading that I knew was appropriate to the situation? I of course want to know the gauge is indicating true temperature in the event of overheating. Thanks for your well expressed and accurate info.

 

the temp gauges have a built in 'hysteresis' circuit that keeps the needle close to dead center as long as the operating temperature is anywhere near 'normal range'. it only climbs above the dot if its approaching overheating, and then rather quickly pegs.

they did this to stop neurotic owners from badgering service departments with complaints about too hot, too cold.

this is, IMHO, annoying but its too much trouble to circumvent, except on earlier 240s where there's a little circuit board sliver stuck into the main instrument panel board with this hysteresis circuit, you can bypass it and then the needle goes up and down with warmer/cooler operation. I've toyed with doing the same on my 1992 740 but it would require tracing out the whole circuit board and doing a bunch of tests and analysis, and meh, I'm too lazy.

 

oh, your 86 has that board. here's the kit to bypass it.
Volvo Temperature Board Bypass Kit IPD 108262 1363K

 

and, if you disconnect the yellow wire from the temp gauge sensor at the engine block, and GROUND the wire, turn the ignition on, your gauge should peg at overheating. if it doesn't odds are, the temp compensator circuit I described above is bad.

 

Post 4, paragraph 5.

Ground the damn thing.

 

Wow Pierce. They missed out when they were reverse engineering UFO's; they should have hired you! That biz about circumventing the compensator unit on the temp circuit - who would even imagine such an option would exist! Thanks. I hope grounding the circuit gets the right reaction - I have an entire other unit - sensor to new gauge, ready to try - but can't determine if the threads on the new unit are metric as they LOOSELY fit both a standard adapter and a metric adapter! I could use teflon but if that melted under heat I'd have a mess.

If you have a moment . . .the 'bad bulb' warning light on the dash went out as both right running lights went out. I checked the wire connections and looked at the schematic but have no idea where bulb circuit links to the warning sensor - so I just ran a wire from the working left rear running light to the right light and both right running lights came back on - BUT the 'bad bulb' running light still goes on - but only when I press the breaks?!?

 

Okeydoke. I'll ground the damn thing.

 

the various bulbs are wired THROUGH the bulb-out detector, eg the detector is in series with the bulbs. the detector consists of counter-wound pairs of coils around a magnetic reed switch... if the current to the left bulb circuit is different than the current to the right bulb circuit, the reed closes, and lights the bulb-out light.

 

I see, the 'bulb out' circuit isn't an actual thing but a kind of electrical balance. The reason I re-wired the lights was because I put in a new bulb and it didn't do anything. Does is make sense that both right side bulbs went out at the same time? Doesn't that mean half that circuit is bad? The fuse is OK. I'll have to check all the connections again. I don't want that bulb out light coming on all the time.

I did ground the damn temp gauge wire and it DID go to HOT. So I guess it works . . .