Vauxhall Vectra wiring - trailer socket

15 Nov 2005
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United Kingdom
Hi folks
Recently fitted a towbar to my 1999 Vectra estate. No problems there.

Got a simple wiring kit with it and a load of Scotchloks. On inspection under the boot floor I found what seemed to be a socket for trailer wiring so I thought I could probably use the Scotchloks and splice into that loom.

To confirm, I grabbed my Haynes manual and found the wiring diagrams and this seemed to confirm my suspicion.

Once it was all Scotchlok'd in, I grabbed my multi meter and attempted to test the continuity of each join. Not so easy because there isn't much bare metal to touch. So, my method was to get one probe onto the blade of the Scotchlok, and the other probe to touch the core of the wire that was visible. However, where I was splicing into the car's socket loom there obviously isn't any visible core so I was following that wire and checking the corresponding pin in the socket.

All seemed to be fine after a bit of extra squeezing on the Scotchloks. Plugged in a brand new light board and I didn't get the desired results. One of my tail lights flashed when indicating left, but very little else happened. So I went back and checked I'd joined the correct wires.

Still no success. I then used the MM to check the wiring in the light board. That seems to be fine. I then checked the wiring in my towbar socket. That seems to be fine.

So I called the tech support. They suggested using a more reliable earth than the one in the car's loom, so I put a screw into the floor of the car and wired the earths to that. That produced some better/different results. Indicators appeared to work, as do tail lights, but not the brake lights.

Tech support suggested that the brake light wire can sometimes be a problem on this car, so to splice into the main loom of wires in the boot instead. However, this loom has 2 black&yellow wires - 1 is the brake lights, 1 is the low fuel warning! I used my MM to check continuity between one of them and the bulb connection and believed I had the correct wire. However, the results are the same.

What I want to do is make a testing device that lets me clip onto a wire and an earth, then check that the wire is what I think.

Can someone give some tips on making the tester, or on how to do the wiring? Tech support isn't available outside office hours and I never have the car during office hours.
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Try to make a better earth that a screw screwed into the floor. Try to find a bolt, maybe one of the bolts holing the light cluster in? If you had gone to Vauxhall, you could have got the wiring that plugs straight into the one on the car. For a tester it's goot to use an old car horn, that way you can hear it and you don't need to keep looking at your tester. Connect one end to battery - or a good earth, then with the other end on a long piece of wire connected to a probe and beep beep.
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The Vauxhall supplied plug is somewhere near £50. I'm told by the company I bought the towbar and wiring from that my year of Vectra shouldn't need any special kit so the method I'm trying to use is suitable for a DIY effort. The company have years of fitting experience using the same kit as supplied so I have no reason to doubt them.