Trailer lighting board.

blueboy758 · 24 February 2009, 08:03

what settings do i need for a voltmeter to be on whilst checking one side of the board as the other works fine and the bulbs in the U/S side are fine!

phil

JABS · 24 February 2009, 08:27

12 volts, so probably 20. and DC.

Sounds like a grounding problem.

Nos4r2 · 24 February 2009, 14:41

Test it from socket to trailer plug, with all the bulbs out and the board not plugged into the car.
Use the lowest ohms setting (or Continuity if it's got it)on the multimeter. That way you'll at least know if the wiring is intact.

If you're not sure the bulbs are OK, test them the same way. You'll get no reading if they are blown. Compare the results of the 2 stop/tail bulbs. Sometimes (rarely) they internally short between filaments which can make odd things happen.

Then,test the earth side of the bulb sockets to a negative on the car (Towbar should be earthed, with the board plugged in and the car turned off.

there's no point in testing it on 12v DC-the light bulbs are a pretty good indicator that it's getting power

jyasaki · 25 February 2009, 15:43

Checking continuity from one pin of the bulb socket to the trailer connector is a pain, as you need to have really long ohmmeter leads. Simpler is to remove the bulbs, then at the trailer connector, short the ground wire to the conductor you're testing (i.e. running lights, right turn/brake, or left turn/brake), then read across the bulb connector. You should see a short if the wiring's good.

If it's not, you can isolate which wire is bad by cross-connecting (left turn to right turn and reading left bulb center to right bulb center, say.)

Alternatively, you can jump 12V into the system (negative to the white, 12V to all the others) and see where the voltage doesn't show up.

jky