Javelin windscreen wipers

[strathmore22]

Hi. Can someone please help me with my problem with my Javelin windscreen wipers?

The wiper motor works fine when connected straight to the battery.

The problem is that there is no voltage arriving at the connections to the wiper motor.

My meter tells me that one of the connections connects to earth (positive) when I switch the W switch on, which I would expect. The other connection tells me that there is 12 V connected when I switch the ignition on, which I also would expect. What I cannot understand is that there is no voltage at all going to the motor connections when I start the engine and switch the W switch on.

[Forumadmin]

Your meter is reading voltage. so if you have a positive earth on the Javelin then with the red lead connected to the chassis ( not the battery terminal) and the black lead connected to the negative terminal of the battery you should read about 12.5v when engine not running and 14.7 when it is. Keep the red lead to the same chassis earth and trace the NEGATIVE CIRCUIT FROM THE BATTERY TO THE WIPER MOTOR. It goes through fuse, ignition switch, wiper switch and various connectors.With the ignition switched off you should have zero volts between chassis and both treminals of the wiper motor. When you switch the ignition on you should still have zero volts on one of the wiper motor terminals and 12 v on the other. This will tell you if the break is in the negative (feed) cable or positive (earth) cable to the motor. If you have 12v on both terminals the problem is in the earthing cable. If there is a small voltage (.1 to 1v) on the earth side of the motor then this could indicate a poor earth such that the circuit cannot deliver the current required by the motor.

[strathmore22]

Many thanks. I will make more tests next time I get a chance.

[Nick Webster]

The heater motor uses some of the same supply wiring. Does that work?

Nick

[strathmore22]

Hi. Thanks all for your info. Does this mean that the car earth is not the same as the positive terminal of the battery? I wasn't sure whether your detailed instructions meant that the motor should be connected at the time. However, I have found that the motor works if I connect its positive terminal directly to earth, so I will have to do that together with its own switch. The heater has worked throughout. Thanks again for your concern.

[Keith Clements]

The battery positive terminal should be at the same voltage as the chassis and every component's return path but because of current flowing thought the return circuit and it's resistance small voltage differences will occur. Usually rust and galvanic corrosion cause these resistances to increase to the point that the voltage required to drive the component causes it to stop working. The same is true for the feed circuit but this is usually copper wire with a few connectors and switches in the circuit that can also oxidize.

[strathmore22]

Thanks Keith. I will bear that in mind.