Hi all,

I have a westfeild megablade with vdo gauges. I've been having an issue with the gauges where they are bouncing randomly. examples are:

1. driving along and the speedo will show 0 although doing 40mph. it will then bounce to 60mph and then to the correct speed that i'm going at no pattern to this;
2. driving along at around 6k revs and will drop off to 0. few minutes later it come back. if i drop a gear then still remains at 0 so not like its getting stuck again no pattern;

volt, oil, temp and fuel all fine and don't bounce. I noticed whilst out tonight when i had my lights on that voltmeter dropped below 10 when usually just over 12. When i put the indicators on it dropped to around 8 and i noticed that both the speedo and rev gauges started bouncing all over the place.

the battery is new.

Any ideas what this might be? i'm stumped.

cheers

Is your alternator charging anything below 12.4V is not!

Sorry pal. I don't quite get that. Are you saying the alternator is not charging? If you ignore the lights / indicators then it still does it at random with no strain on battery. Cheers

Have a good clran up of the battery connections, both of them and the battery to earth connection.

Caused me a few issues.

does sound like the alternator isn't charging, sounds like electrical surges

It needs to be reading 13.8v to be chargin.

Also check your earth. Most gauges are resistor based and have a narrow band. If they don't get good supply they don't work. On the flip sides your senders need good earth's so make sure you have earthing straps for anything rubber mounted.

Last of all it may be broke. I had an oil temp gauge that just read over by 15 deg. New one was spot on.

Sounds very much like poor connection, first place to start looking is the connections at the alternator, these carry high current and are subject to vibration, dirt and heat. If you have an alternator with the bold style Lucas 3 blade connector these are particularly prone to arcing.

Also check your battery connection and earth wires especially as you have had the connection off to change the battery.
Your battery voltage should be fairly steady between 13.4 and 14.9 volts at 2500 rpm, and remain in that range when you switch the head lights on and then off again.



[Edited on 22/5/15 by britishtrident]

Thanks for info guys. Back from holiday so will look at this tomorrow and post back. cheers

My Indy Bird would do this when the battery was low. It was the first sign of what turned out to be a failing regulator. As you have found out, low voltage gives bouncy/not working gauges. Although in my case I had the stock Honda gauge pod, but I assume the basic reaction is the same.

Not sure it will help but I used to have a CBR600 which would periodically have a flat battery if I forgot to put it on the trickle charger. Once Jump started for the first 10 minutes of riding or so the dials would be bouncing as though there was a loose connection. I would say your problem is related to low power getting to the gauges.

Thanks for all you help on this guys. BT was right saying the battery should be steady between 13.4 and 14.9 volts at 2500 rpm. Mine was always at 12 volts. With everything switched on it went to 9 volts and engine started to splutter. Traced all the wires back and there were two wires touching where the three wires from the alternator terminate (sorry i don't know the right terminology - i'm a newbee!) Once separated i fired her up and straight to 14 volts. Turning lights on had no effect so working as should be!

Thinking this through, i'm surprised i didn't run out of battery when when out as i expect it wasn't charging or perhaps it was just charging intermittently which may have explained the random dial bouncing if it was getting surges.

Just replaced friction plates, steels, oil and filter and it works like a charm. Finishing work early today!

Thanks again.