Testing the bike rack (Thule RideOn) as we’re going away this week. Neither of the indicators work although the buzzer sounds when the bike rack is plugged in and the indicators turned on. Exactly the same happens with a trailer plugged in.

I thought the buzzer only sounded when there was a current so how does the buzzer work but no indicators? Obviously a problem with the connection on the car itself, is it most likely to be the socket itself?

get a pin out for the socket

test for current at socket on correct pins.

if (no current)
continuity test between pin and connection to indicator wire.
else
continuity between tailboard pin and in indicator housing.

If you’re still having problems I even if you have good continuity and current I would replace the buzz box as I have had one go bad where it would buzz but no indicators would work. Probably even though there was continuity in my case there resistance was too high and not enough current could flow. Either way replacing the buzzing box worked.

N.B.
Connection direction on the bzzing box matters at it has diodes in it.

I know it’s not a fault with the bike rack as the indicators do exactly the same thing when I plug a friend’s trailer in.

Guess I’ll have to go looking for the buzzer

Never assume.

You still need to test for current at the socket even if you don’t test the lighting board.

Faulty buzzer found.

Taking the buzzer out of the circuit means everything lights up as it should, so just need to buy and fit a new one.

Onto the next job – replacing the battery when the new battery bears little resemblance size wise to existing but apparently it is the right one…