240 Bootlid Issues (1989 240 Wagon)

morch_66479morch_66479 @morch_66479 Melbourne, VIC
edited June 21 in Troubleshooting

Hi All,

My rear defroster isn't working but when I checked voltages at the terminals either side of the rear window I get ~11v when ON and 0v when the switch is OFF. However I don't hear a realy click when I toggle the rear defroster switch.

Should I hear a relay click and is the relay/switch timed to turn off the rear defroster after a period of time?

The wiring in the boot is ok as far as im aware and I replaced the wiring in the boot hinges earlier this year.

However I also have an issue with the intermittent rear wiper - it does an 1/8 of a sweep every 8 seconds and won't do a full sweep. Also to this the constant ON option won't return to home when i turn the stalk off. I need to watch the rear wiper and when it sweeps to home it then knock the switch off.

Anybody came across this scenario or have any tips on how to proceed with a diagnosis or repair?




  • Assuming it’s a 240 wagon, correct? Given you have identified power to the rear glass terminals, the only other issue I can think of is a bad connection either between the wire and the glass at the terminal, or the terminal attachment to the glass...or possibly the silk-screened “wires” on the glass are damaged?

    Depending on what year it is, the rear defog switch is either a toggle on/off switch (earlier cars) or a momentary push switch that returns home after pushing (later cars). The early cars most likely do not have a relay, and there is no timer - just turns on and off manually with the switch. On the later cars, unless I’m confusing it with the heated mirror switch, there was a timer relay that shut off after 10 minutes or something like that.

    With respect to the wiper issue, I would suggest double-checking your wiring repair at the tailgate to make certain you got the correct wires on the correct terminals...also could be an issue with the intermittent wiper relay or the wiper contacts in the motor could be dirty. Confirm wiring is correct first, then swap out known good relay, then check wiper motor contacts - my suggested order.

  • Ex850RSnoopy @Ex850R Somewhere Over the Rainbow. Melbourne.

    Considering the age of parts and wires and unknown previous work done the only way with issues is to get out the electrical test tools and test every part and wire . Or just wire up complete new circuits as a car electric guy once told me, no point even using the old stuff,just rewire it and save time and lots of money chasing old junk for problems.


  • Perfect info @carnut222 ,

    Yes its the 240 wagon. I checked a few of the silk-wires already and have 11v on them (which means it should work right?) but haven't checked all of them just yet. My thinking was that if one wires was broken then it prevents the entire rear window from defrosting but i dnt' think this is the case?

    Mine is the ON/OFF switch so that's why i don't hear the relay. I might go back in and check the wiring in the boot, Can i do any voltage checks in or around the wiper motor to confirm that the wiring in the bootlid hinge is connected and working correctly - just trying to avoid taking the hinges apart here that's all?

    Where can I find the rear window wiper realy? Is it near the radio somehere?

  • Yes you can probe the wires inside the tailgate by removing the inner trim cover. The wiper delay relay is located in the left (passenger) front foot well - usually under what would be the foot rest for the left-had drive cars. Remove the under-dash hush panel and pull back carpet. There will be 2 relays - one for front and one for rear, can’t recall which colour is which. You could remove one and try wipers to see whether you got the correct one.

  • Angus242164Angus @Angus242164 Western Victoria

    The demister on these is a very basic circuit, power to the switch via a fuse, then to the element. No relay or timer.

    If you check for voltage between the element positive terminal and the body, you can see whether the low voltage condition is occurring before the element.

    You can do this with the element unplugged as well, the 11v might be normal once the load of the element pulls the voltage down from battery voltage.

    Use an ohm meter between the element earth terminal and the body to check the integrity of the earth path between the tailgate and the body.

    You can also run a wire from the element earth terminal to the body and see if the performance changes.

    No point messing with the wiring in those hinges unless your testing indicates that a fault lies in that area.

  • Angus242164Angus @Angus242164 Western Victoria

    The tailgate wiper motor may have an internal fault, but it might also be a poor earth. Try running a wire from the motor earth to the body and see if that changes the behavior.

  • morch_66479morch_66479 @morch_66479 Melbourne, VIC
    edited August 2019

    So I finally made time to look at the demister.

    I used a 12v circuit tester (globe) and the globe lights up as normal between the 2 element terminals but when I test the individual lines (working left to right)

    The globe gets dimmer and dimmer across the window as I work my way right so basically I get a steady voltage drop along the lines and drops to 0v half way across.

    My earths are good with normal voltage drops (under 0.02v)

    I ran a wire from the element to body earth with no success. I also ran a wire from battery positive to the other element with no success. Still get a voltage drop across the rear window.

    I did find another issue where water is getting into the wiring since I replaced the boot hinges a few months ago but don't think this is the reason for it not working as I've ran new complete new wrong to the elements.

  • Why would it lose voltage across the window. Is this normal wear?

    I also noticed that one line has no voltage reading whatsoever, would this effect the circuit? Surely not??

  • Following up Angus is correct and I was wrong about the switch. I was confused about the momentary (with timer relay) heated mirrors switch on the 93 wagon...as Angus said it’s a simple switch no relay or timer on all 240s including the late ones.

    Did you check the continuity between the two sides of the heated window (ie the + and - sides) with the wires disconnected? Seems to me there should be a spec for it in the greenbook manuals (maybe?) or one of us could compare to our working window heater for you. What year is the car? I have 77, 79, 81, 91 and 93 wagons and I’m happy to do continuity tests for comparison if you provide a value.

    I think the simple answer is if you hook a 12V battery up to the left and right terminals of the glass and you get no heating function (may be hard to test!) then your defrost grid must be damaged (either the grid itself or the terminal connections to the grid).

  • I an't seem to disconnect the wires on the elements but I'll have another go at it tonight.

    I'll try get more figures for you tonight. My car is 1989.

    The wiring i ran was pretty much like hooking up a 12v battery to the rear demister and it didn't work so its looking like it is a defrost grid issue :-(

  • Yeah I don’t see how it could NOT work by hooking up 12V to it unless the grid is damaged. How do you know if it’s working though? Unless there’s fog or frost on the glass when you test it...or can you feel the glass getting warm when the defogger is on? I’ve never tried it myself!

  • From memory you can see feel a bit of warmth in the glass, I also tried breathing on it last night but it didn't clear it.

  • Angus242164Angus @Angus242164 Western Victoria

    A trick for testing is to create steam under the glass, eg: a pot of hot water on a cold day so it condenses on the cold glass.

  • Angus242164Angus @Angus242164 Western Victoria

    I'm pretty sure that full voltage at the + end of the load and 0v at the - end is normal.

  • Interesting, that's throws a spanner in the works!! Is this something anybody could check against a working defroster to clarify this?

  • Angus is correct - if you put your multimeter black probe on the - side and red probe on the + side with the defroster switched on, it should be ~12v. If you then move the red probe (carefully) along one of the wires, the voltage should drop as you move across the wire towards the - end. It seems like the defroster should work even one or several of the grid wires are damaged (the current will just flow through the remaining wires)...this website has a few generic helpful hints:


  • How'd you go on this issue? I was just looking at some wiring diagrams and I see the 91 and 93 have a timer relay for the heated rear window (but still have the normal rocker switch). I wasn't aware of it. Yours may or may not have the relay (not sure when the timer relay was introduced??)...might have to follow wiring from the switch?

  • morch_66479morch_66479 @morch_66479 Melbourne, VIC
    edited June 21

    This task is still on my to do list as I've started working FIFO again. I have a few issues to sort out in the boot:


    Boot hinge - let side

    Seals for wiring and hinge components

    Wiper motor

    I think i need to dedicate a day to all of this but just haven't had the time.

  • Update time:

    1: Installed new wiring in the boot lid that runs back through the hinges and into the car

    This has resolved the intermittent wiper issue and the home/park position.

    However the demister still doesn't work, here are some figures:

    • 13.3V when I check voltages between the terminals on either side of the grid.
    • I'm getting continuity and have 6.55 Ω at the terminals, if i check the Ohms further upstream within the bootlid it's 6.51Ω

    I know there is a couple of stripes broken and was considering using this kit to see whether it effects the system operation:


Sign In or Register to comment.