13-pin socket tester

Possibly not the right place to post this, but it needs to be available locally (Hereford or Worcester). Admin please move if you feel the need.

Does anyone have a electrical tester for 13-pin towbar electrics?

I've just fitted some to my car and want to find out if it's all OK before I plug something expensive in and blow something up.

The cheapest on eBay is £33 which is too much for one use. That's the type that doesn't need the trailer ugged in as well and tests just the car electrical side.

Ideally this weekend if possible. Thanks.