MJ controlled rad fan triggered by indicators!

[Quagmire]

Guys,

I know this is probably an earth problem or something and wanted some advice on where to head to first.

Some background:

My radiator fan was bought as a complete kit from Kenlowe, and as such was up until recently set up as standard, with the temperature being sensed by the capillary unit in the rad hose, which then switched a relay to provide power to the fan.

I have disconnected the Kenlowe capillary based switch, and replaced it with another relay. This is connected to +12v on the trigger side, and then connects to Ouput1 on the MJ so that when MJ switches to ground on that pin the relay is triggered.

All that happens then is that the switched output from the relay is connected to +12V side of the relay that switches the fan, which is then earthed nearby.

This all works well, and the fan is triggered on and off by MJ quite happily.


The MJ reading for water temp is taken from the original single terminal temp sender located in the inlet manifold (its a rover v8). The original function of this sender is just to drive the water temp gauge in the dash.

All i have done is add another short "y-piece" with spade connectors to allow two things to be plugged onto the single terminal simultaneously. If it makes any difference, the gauge still reads as before- with the needle sitting bang in the middle when at normal running temp.

However, i have noticed that when i have my headlights on and I indicate or brake then the fan is triggered! I have tried all other combinations of devices, i.e. cabin heater on and off, sidelights only, no lights on etc... The fan will run for a short while and then go off as normal, until you brake again

The fan is only affected by the brakes/indicators when the headlights are on.

So, should i be looking at the gauges and their earths? Or at the headlights, and where they earth out? Neither earth near the MJ, which is located in the battery box and earthed to the negative terminal. The water temp sender earths out through the block. I guess i could try disconnecting the water temp gauge from the sender and seeing if that changes things to rule it out.

Suggestions appreciated!

Thanks

[DannyP]

This sounds strangely like an electrical gremlin I had picked up when I added the aux input.

http://www.autosportlabs.org/viewtopic.php?t=2486

Possibly you can disconnect temporarily to see what lead is causing this. Maybe you can isolate this with a couple of diodes, 1n4001 should do it.

[NITROPIXIE]

Alot of standalone ecu's have interference issues with single wire temperature sensors. They suggest its best to use the twin wire sensors which are isolated electrcially from the block and ground at the ecu or ecu ground. Which does kind of make sense.

I've not come across it personally but if i did run a setup like this it's the route i would take/try. There must be a twin wire sensor which should fit somewhere???

[DannyP]

Right you are Nitro. I had my problems with the sensor hooked only to the Megajolt, my interference was from my turn signals. I did however purchase another sensor for the gauge, so I have two electrically separate sensors.