Posted: Thu Dec 02, 2010 8:31am

I have an 18 month old Aqualine with Isuzu engine.When running recently, the temp, oil pressure and volt meters all show ok, but the rev counter needle droped from 900 rpm to the bottom, and the hours run meter started flashing, so cannot read revs, what has happened, and how can I put right Thanks, Dave

Posted: Thu Dec 02, 2010 10:25am

I am going to assume the revcounter and hour meter are combined into one unit. Most of these receive a pulsed supply from the alternator. This tells the hour meter to start timing and the revcounter to count the pulses and convert them to rpm. On the basis of what you tell me I suspect there are no pulses so first of all check the alternator to see if a small cable has fallen off a small terminal. The terminal is generically known as the W terminal but could be marked (according to make) AC, X, R, or AC Tap. If there are no loose or detached wires at the alternator end check behind the actual revcounter. Also search along the main wiring harness for a multi-plug. I you find one try wriggling it about or pulling it apart and refitting it. If this cures the problem you have a dirty/loose terminal inside the plug so see if you can clean dirty looking connections and perhaps try to squeeze up the female half a LITTLE. Then rub silicon grease or Vaseline into the female half before remaking the connections. Once you are assured all that is OK we are left with the possibilities of: broken wire, faulty alternator,or faulty revcounter. Please note that the alternator may well still charge to a degree with a typical fault that causes revcounter failure. If you have a multimeter set it to a Hertz (Hz) (frequency) scale if it has one and connect it between the W terminal and the main B- terminal or the case. Start and rev the engine. The meter should rise and fall with engine speed. If the meter does not have a HZ scale set it too a low AC Volts scale and repeat the test. IF the Hz does not rise and fall or the AC volts remain very low or do not rise and fall it is the alternator that is faulty - you have a diode failed. If you do get a rise and fall on the meter the chances are you have a faulty revcounter, but first double check its positive and negative supply. Tony Brooks

Posted: Wed Dec 08, 2010 9:35am

Thanks for info, will check as suggested.