Mercury Rev Counter

[The Hoff]

Hi Ribnet,

I've just bought a Apex RIB with a 2001 Mercury 75hp 4 Stroke engine which i'm really pleased with but was wondered if anyone could help me with a wiring issue regards the rev counter, please?

I've got power as the back light works, when the ignition key is turned on, the needle slowly rises until it stops at 8k rpm. When the engine is turned over, the needle goes off the scale!!
When power is off the needle then goes back to 1.5k rpm!

I'm really no wiring expert, just managed to change the switch panel and wire the nav lights working which gave me great delight.

Any help would really be appriciated. I've attached a few photo's so you may spot the problem straight away :-)

Thanks in anticipation

Andy

[spartacus]

Got the right polarity setting on the tacho?

[The Hoff]

Thanks spartacus for your reply.
If i'm honest I am not sure what the polarity should be set at so am unsure if it is right, any ideas?
Cheers Andy

[gotchiguy]

Originally Posted by The Hoff

Thanks spartacus for your reply.
If i'm honest I am not sure what the polarity should be set at so am unsure if it is right, any ideas?
Cheers Andy

There will be a little switch on the rear of the dial which can be turned ~2-6. Try each setting, one should work. Basically the dial is given a certain number of pulses per revolution but it needs to know how many pulses it will get per revolution so it has to be told otherwise it won't work. It depends how many magnets there are on the flywheel and therefore how many pulses the dial receives per count.

But I may be talking complete rubbish

[spartacus]

Originally Posted by gotchiguy

Basically the dial is given a certain number of pulses per revolution but it needs to know how many pulses it will get per revolution so it has to be told otherwise it won't work. It depends how many magnets there are on the flywheel and therefore how many pulses the dial receives per count.

But I may be talking complete rubbish

Sounds convincing. Ever thought of going into politics!

[doggypaddle]

summat strange going on there, dont think its the switch setting though, if the ign is on and the engine not running the needle should go to zero not 8K, with the ign off the needle could stop anywhere, mine usually goes to about 2krpm too.
I would say if you have a 12v supply getting to it of the correct polarity then it may be faulty.

[doggypaddle]

Originally Posted by gotchiguy

There will be a little switch on the rear of the dial which can be turned ~2-6. Try each setting, one should work. Basically the dial is given a certain number of pulses per revolution but it needs to know how many pulses it will get per revolution so it has to be told otherwise it won't work. It depends how many magnets there are on the flywheel and therefore how many pulses the dial receives per count.

But I may be talking complete rubbish

pointing to 8K without the engine running though??????
must be set to the 0 pulse setting
seriously though I dont think the switch position should effect where it sits at 0RPM. zero rpm is zero pulses whatever the setting.
if it reads 8K its either got the wiring wrong or its fekkt

[Polwart]

Originally Posted by gotchiguy

But I may be talking complete rubbish

Unusually accurate but it will probably be the signal from the alternate rather than fly wheel. I think on this engine you should try position 4p on the little black dial on the back.

[Polwart]

Originally Posted by doggypaddle

pointing to 8K without the engine running though??????
must be set to the 0 pulse setting
seriously though I dont think the switch position should effect where it sits at 0RPM. zero rpm is zero pulses whatever the setting.
if it reads 8K its either got the wiring wrong or its fekkt

Agreed, perhaps wired wrong, can't see in pic.

[doggypaddle]

Originally Posted by Polwart

Unusually accurate but it will probably be the signal from the alternate rather than fly wheel. I think on this engine you should try position 4p on the little black dial on the back.

Isnt the alternator rotor the flywheel on a 9.9? and the stator inside it