Rev counter moves when heater fan is altered

[Simes 248 2 Cars]

Hi,

 

Whilst the engine is running my rev counter moves independently to the engine when you adjust the fan speed, the battery light seems to come on too on full fan power.

I've investigated all the major earths and then played around with the fusebox but then ran out of time. This is the thing I don't have!!

 

Could anyone shed some light - is it going to be a case of bypassing all the earths to these feeds and taking it directly from the battery??

[pugdamo 111 2 Cars]

Have a look at the positive cable from the battery to the shunt box, seems to be quite a common issue now and fits your symptoms. Mine has started to fray but something always seems to get in the way of getting a new lead. 

[jackherer 543]

Check the alternator too, what voltage are you seeing with the engine running?

[Simes 248 2 Cars]

That’s next on my list. Last time I had one starting to fail all the running lights did a Christmas tree effect!

[Simes 248 2 Cars]

Well. 

Alternator is running at 13.8v running and it's 11.8v when off - says my Emerald.

I can make it do it with just ignition on.

 

Switch on ignition

Let the pump prime.

Then I think the Emerald initiates the rev counter needle to spin (I guess a test?).

Don't fire it up.

After that if you switch on the fan blower, indicators or similar the rev counter reacts with it, a bit like an ammeter!!!

Dodgy rev counter?

[jackherer 543]

Is your tacho modified or adapted to run off of the Emerald tacho output? If so the initial movement could be the peak RPM tell-tale function on the ECU.

 

The tacho has it's own 4 pin multiplug on the back so it's very easy to trace the wiring for that, if it has an adaptor between it and the Emerald there might be an issue there like a bad earth.

[Simes 248 2 Cars]

Dodgy earth I think.