NL no stop lights troubleshooting

[jeans]

Hi, I've got a -98 NL with a tow bar and cruise control that currently does not have any stop lights. I was hoping someone might be able to help me think through the troubleshooting and figure out the cause of this.

What do we know:
- 15A fuse "STOP" under driver side dash is good
- 12V in the fuse box (in the position for the STOP fuse)
- Brake light switch is working, bought a new one just in case and tried but same issue
- All other lights work well (hazard, position, reverse)
- Stoplight bulbs are good - none of them are broken and none of them are getting any voltage
- Trailer connector has same issue - all other lights work but no stop lights

Observations that I've made that I don't understand:
- In the brake light switch connector, there's approximately 7V between two pins - why is this not 12V?
- Cruise control is not working - suspecting that this is related
- ABS light comes on after approx. 10 minutes of driving. ABS works before light comes on and stops working once the light is on (tested on loose surface)

If anyone is able to point me in the right direction or has any ideas on what to investigate next, that would be great!

Thank you very much!

[disco stu]

Is there a plug underneath for tail lights? I thought I saw one the other day when I was under there. If so you could at least test for power there

Personally, my first point of call would be the trailer wiring. For some reason everything to do with trailer wiring seems to be done by untrained monkeys in the most dodgy way possible. Dodgy clips instead of soldered connections etc. Check the wire isn't been damaged from that connection

[disco stu]

Have you checked all cigarette lighters etc work fine as well? I seem to remember a relationship between one of the cigarette lighters and other seemingly unrelated parts

[nj swb]

The cruise control needs to know when you've braked, so it doesn't keep accelerating. The 7V might be something to do with monitoring the brake switch. Once (whatever) concludes there's a problem with the brake switch, both cruise control and ABS are cancelled?

Beyond this, not sure. Do you have a wiring diagram for your car?

[jeans]

Is there a plug underneath for tail lights? I thought I saw one the other day when I was under there. If so you could at least test for power there

Personally, my first point of call would be the trailer wiring. For some reason everything to do with trailer wiring seems to be done by untrained monkeys in the most dodgy way possible. Dodgy clips instead of soldered connections etc. Check the wire isn't been damaged from that connection

Thanks for replying!

I'm not sure what you're referring to re the plug. Are you thinking about a plug / connector in the rear from the harness to the tail lights? Those connectors all seem fine as all other lights work however, there's no voltage for the brake lights in any of them.

Agree re the trailer wiring. I've been following the wiring that's external and it all looks fine. I haven't yet pulled the interior cladding on the driver's side back seat / wheel arch. I believe there's supposed to be some sort of trailer box / ecu underneath there? It would be great if someone could confirm this.

Re the cig plugs, I've got two working ones in the front. One just on the left side of the steering wheel and one just ahead of the drive selector (4WD/H/L). The one in the middle of the consol, behind the gear lever and to the left of the handbrake is dead.

While trailer wiring sure often is dodgy, I still find it weird that I'm only getting 7V in the connector to the stop light switch and this makes me think that maybe the fault is all the way in the front. Thoughts?

Thanks!

[jeans]

The cruise control needs to know when you've braked, so it doesn't keep accelerating. The 7V might be something to do with monitoring the brake switch. Once (whatever) concludes there's a problem with the brake switch, both cruise control and ABS are cancelled?

Beyond this, not sure. Do you have a wiring diagram for your car?

Agree, the cruise control not working due to the same fault seems perfectly logical. I've got the service manuals that I've downloaded via a link on this forum but it doesn't seem to have the detailed wiring diagrams as far as I can see. Are you aware of where I might find more detailed diagrams?

I do have a basic wiring diagram which is supposed to be helpful when installing the trailer wiring but it's not really saying much.

I guess if the 7V has to do with CANBUS monitoring rather than actual power feed to the lights, maybe the connector isn't actually getting any voltage at all. I might have to dig deeper into the wiring under the dash and see if something is off.

Other ideas on how to eliminate stuff are very welcomed, thanks for replying!

[Mikesherwood]

Hi Jeans, wondering if you got a fix to this problem, i have what seems a very similar issue... cant figure out the cause and solution