Really weird Reverse lamp issue.... I can't understand it.

#1
The reverse light on my K12 isn't working.... I had thought it was a reverse light switch issue as that seems quite common.

So I got under the car and checked the switch with a multimeter, there was continuity between pin 1+2 and also 2+3 (2 being the shared live). So I popped the car in reverse and checked the wiring loom to the switch and I was picking up voltage between the plug connections.

To the back of the car and checked the actual terminal, with the multimeter and again with the car in reverse there was a clear 12V shown (when connecting the multimeter + to the brass prong that touches the bottom of the bulb and - on the silver metallic housing. Taking the car out of reverse and the voltage dropped to something like 0.005v, so I'm thinking the whole circuit is working correct?

So I thought it must be the bulb, I got some new ones but still the light did not work, I checked them for continuity and the bulbs were fine. I though perhaps the brass prong wasn't touching the bottom of the bulb so I bent it up a bit and still no light.

Now I may be missing something really obvious here.... or perhaps I just have the wrong bulbs.... but if I have voltage at the bulb the damn thing should light...... shouldn't it?
 

John_D

Club Member
Radio Code Guru
#2
Mine did the same, turned out to be a high resistance connection in the loom plug that connects to the rear light unit. (12 volts vanishes immediately a load is put on it). One word of warning be VERY careful not to remove/refit any bulbs in the lamp unit with power to them. I managed to momentarily short the feed to the rear light bulb which blew a fuse. Sadly all of the lighting fuses are in the main control box which is underneath the N/S headlight which has to be removed to get at it!!
 
#3
Mine did the same, turned out to be a high resistance connection in the loom plug that connects to the rear light unit. (12 volts vanishes immediately a load is put on it). One word of warning be VERY careful not to remove/refit any bulbs in the lamp unit with power to them. I managed to momentarily short the feed to the rear light bulb which blew a fuse. Sadly all of the lighting fuses are in the main control box which is underneath the N/S headlight which has to be removed to get at it!!
Thanks for the info...

High Resistance connection in the loom plug?.... how did you work around or fix that then? all of the other lamps are working fine..... well there was a moment earlier when I was playing with this lot (see pic) that I must have crossed a wire or something because the right indicator was instead causing the right brake lamp and the number plate light to flash.

I'm truly shocked by the wiring on this vehicle, it seem brittle and poorly protected. The loom as it fields into the hatchback is a perfect example... I've been trying to sort this mess out today as the rear wiper and heated rear screen are not working. Clearly a fix has been attempted before but it wasn't done very well and the wires have fatigued again, hopefully my fix will be a bit longer lasting (I still need some larger core wire for the heated screen).
 

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#5
Yep horrible isn't it Mika.... just need to connect up the heated screen how.... then pull up the rubber gromit, sleeve and try and seal it from rain etc..
 
#7
Yeah I'd like to but it's going to be difficult trying to desolder that lot and stick new wiring in as there just isn't enough slack in the cables. Really a new loom needs to be pulled through but i can't be bothered with the hassle and expense of that. Some bullet connectors have give me a little bit more length in the broken connectors. I still need to do the heated screen as i didnt have a spate bit of the correct gauge wire. Then I'll just have to take it up and make it rain/moisture resistant. It won't look great but it should do the job and probably out live the rest of the car.
 
#8
Yeah I'd like to but it's going to be difficult trying to desolder that lot and stick new wiring in as there just isn't enough slack in the cables. Really a new loom needs to be pulled through but i can't be bothered with the hassle and expense of that. Some bullet connectors have give me a little bit more length in the broken connectors. I still need to do the heated screen as i didnt have a spate bit of the correct gauge wire. Then I'll just have to take it up and make it rain/moisture resistant. It won't look great but it should do the job and probably out live the rest of the car.
Improvise, adapt & overcome any problem in the quickest, simplest, easiest & cheapest way to get the job done, & working is the way to go? Aesthetics looks that are out of sight hardly matter on an old vehicle. ;)
 

John_D

Club Member
Radio Code Guru
#9
I'd be tempted to cut the existing loom where the mangled bit is (probably be smart to disconnect the battery first) connect SECURELY a draw cable, at least a couple of meters long, to the tailgate side, then remove the lower tailgate cover and pull the cable back into the tailgate till the broken end can be accessed through the hole, detach the draw cable , trim back the loom to good wire then add new wire to each 'good' cable ( a foot or two of new colour coded wire), wrap in tape and reattach the draw cable VERY securely, taping in a very smooth cone that cant catch up on anything, then draw the new cable back up and out of the hole at the top of the hatch back.........remake the new wires to the wires that are coming out of the body.......
 
#10
Yes John I may well have to do that in the end but for the moment I'm going to try patching things up and see how it lasts. I don't like bodging things really but I'm a bit strapped time and don't want to spend time and money on an annoyance rather than something that is critical.

The reversing light is the thing that is really frustrating me.... I'm guessing I'm going to have to try to track back the wiring in the loom for short circuitss. As I say there is 12v at the bulb socket on my multimeter. I can't make much sense of the wiring diagram.... Apparently there is "Fuse 50" in the IPDM.... is this even serviceable? also the wiring diagram shows the live splitting off and going into the car stereo as well.... I'm not sure why. I do have a new car stereo fitted now but the reversing light didn't work anyway with the original Nissan stereo fitted.
 
#12
I also tried messing around with the reversing light.... I'm still confused to be honest...

At the bulb socket there is a constant 12 volts.

If you look at the attached photo of the switch you can just make out the terminals and how they are numbered, from left to right 1-2-3.

2 is the switched/ignition live, if I connect an inline bulb to this pin the bulb lights up. The next test was to check continuity and this tested fine between pins 1 (the switched reverse live) and 2 with the gear lever in reverse. I've tried testing various ways but from what I can see there is voltage and continuity. It might be easier if I work back from the bulb socket and cut into the wiring to properly check. I'll have to work out how the loom is routed though, or I might just route a piece of speaker wire from pin 1 directly back to the bulb and see what happens.
 

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#14
I also tried messing around with the reversing light.... I'm still confused to be honest...

At the bulb socket there is a constant 12 volts.

If you look at the attached photo of the switch you can just make out the terminals and how they are numbered, from left to right 1-2-3.

2 is the switched/ignition live, if I connect an inline bulb to this pin the bulb lights up. The next test was to check continuity and this tested fine between pins 1 (the switched reverse live) and 2 with the gear lever in reverse. I've tried testing various ways but from what I can see there is voltage and continuity. It might be easier if I work back from the bulb socket and cut into the wiring to properly check. I'll have to work out how the loom is routed though, or I might just route a piece of speaker wire from pin 1 directly back to the bulb and see what happens.
 
#15
I also tried messing around with the reversing light.... I'm still confused to be honest...

At the bulb socket there is a constant 12 volts.

If you look at the attached photo of the switch you can just make out the terminals and how they are numbered, from left to right 1-2-3.

2 is the switched/ignition live, if I connect an inline bulb to this pin the bulb lights up. The next test was to check continuity and this tested fine between pins 1 (the switched reverse live) and 2 with the gear lever in reverse. I've tried testing various ways but from what I can see there is voltage and continuity. It might be easier if I work back from the bulb socket and cut into the wiring to properly check. I'll have to work out how the loom is routed though, or I might just route a piece of speaker wire from pin 1 directly back to the bulb and see what happens.

K12 circuit diagram with earth locations may help.

https://www.google.co.uk/search?q=c...x-b&gfe_rd=cr&dcr=0&ei=rlSFWoSAGqaLtgf6hL3ADw

Open PDF wiring diagrams 12.15.

Scroll to diagram five, reverse light item 25d.

1) Check voltage across the reverse lamp with a known good lamp in the reverse lamp holder, ignition on & reverse selected. Back probe the connectors as reqd. Should be 12V dc. If not proceed to test 2.

2) With a known good lamp in the reverse lamp holder, ignition on & reverse selected find a known good working earth reference point such as tail & brake lights earth; - Use a test meter to test voltages @ each side of the lamp terminals ( that is the earth Black wire terminal 4 to E4 & power supply terminal 6 Red wire). Note the respective voltages to the known good earth at each location.

Good luck fault finding
 
#16
I also tried messing around with the reversing light.... I'm still confused to be honest...
Never test with a multimeter when there is no load on the circuit. Check the wires to the reverse light with the bulb installed.
Better to get a normal test light probe to check the circuit. If the 12v disappears when you fit the bulb then there's a bad connection somewhere. Fit the bulb and shift into reverse and check pin 1 from the reverse switch. If you have 12 volts, switch is ok. Shift to neutral to make sure that it switches off again. That's first check for the switch. Report back on what you find.

BTW, that bodge on the door wont last.o_O
Easiest way is to get lenghts of wire a few inches longer that the visible wiring. Cut the existing wires about half way and cut off any old solder or crud. Solder and insulate the new wires at the body end and push the wires into grommet at body side. Solder and insulate the other end of your new wires at door end and push into the door. Voila, new wires where they are flexing fitted through the rubber with grommets both ends and all the joins in the door or the body.:)
 
#17
@plmval and @fixK11

Thanks for your suggests, I'm taking another look at it tomorrow so I'll feedback.

As for my "bodge".... yeah I know it's a matter of time before it fails again, but I don't tend to use the hatch much so I'm hoping it lasts at least a few months into the summer, I might be more inclined when the weather is better to start stripping things out. In any case I'll probably look to sell the car on later in the year anyway.
 
#18
So it looks like the reverse light fault is due to a faulty switch and also intermittent, slightly dodgy bulb plate...

I've added various photo's but I haven't worked out how to place them inline with the text so you'll have to work it out for yourselves :p

So starting off at the bulb holder/plate, I found that I couldn't get a multimeter prong into the terminal and no wire was exposed, so I scraped some of the insulation off. The Red wire is the reverse live and the black cable is earth.

Without the bulb removed, with the gearbox reverse switch attached, ignition on and gear lever at the reverse position I get 12.48V when touching the bulb connectors.

With the bulb fitted and this time connecting the multimeter to the Red wire (wire exposed) and touching the earth on the bulb holder plate (as used by all the other working bulbs) I got 11.82V. I tried two other bulbs and got similar readings.

I next removed the connector from the gearbox reverse switch and check for 12V at pin 2 (which was present). I then looped a piece of copper wire between pin 1 and 2 to complete this circuit (as the gearbox switch should). Again I got similar readings as above but still no lighting bulb. This is what was confusing me because clearly voltage is present.

I then took the connect off of the bulb holder plate and connected my multimeter directly to the red and black pins, this gave me 12.19V. I now connected two wires directly to these pins and attached a bulb.....it lit!! I again connected the bulb holder plate to the connect and check my readings again, put the bulb in but again no light. This obviously pointed towards the bulb holder being faulty.

I then realised that both left and right bulb holder plates are the same, so I swapped them over and connected all the wiring together. This time the reverse light was lit, however it's worth remembering I still had the gearbox reverse switch bypassed at this point.

Just for completeness I tested what was the reverse light and now the fog light (having swapped the bulb holders over)....weirdly the fog light did light up so I can only assume that the bulb holder is just a bit dodgy?

With the reverse bulb now lighting the last thing to do was to reconnect the gearbox reverse switch and remove the bypass loop. As expected ignition on, reverse selected, the reverse light failed to light up.

Therefore it seems the switch is the problem and things were further confused by the flakey bulb holder plate. I'm not sure what is happening here, could the gearbox switch be shorting out? I have got a new switch on order and should get it next week, before I remove the gearbox switch I'm assuming it will be possible to connect the wiring and manually activate the switch. If that works then I'll fit the new switch and hopefully all will be good.

If you have any further thoughts or feel I've missed something blatantly obvious then please let me know.

Thanks

Dan
 

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#20
So it looks like the reverse light fault is due to a faulty switch and also intermittent, slightly dodgy bulb plate........Dan
Good work Sherlock:)

Always makes things more difficult when you have two faults. The reverse switch contacts are probably just worn, so not making proper contact.However I have come across wear in the gearbox preventing the switch being pressed when in reverse, but this is rare. If you can remove the switch without draining the oil, then you can check it by pushing it with your finger.
The important thing when testing a problem like this is to use a bulb for testing and not a multimeter. When you connected your bulb directly to the connector and it worked, then you knew for sure that there was enough current, so the only possible fault was the bulb holder.
 
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