will this wiring set up work?

[mollydog]

funny you mention Honda, the original engine for the Elise (so I've been told) was going to be a Honda engine and not the Rover it ended up with, a few people have replaced the Rover engine with a Honda one, not a cheap option though

 

[Richard Burns]

Summary

Lotus Elise with a negative ground.
Radiator fan which is operated by a relay.
An input from the temperature sensor goes to the ECU.
The ECU then connects the coil of the relay to ground.
This closes the relay contacts and connects the positive supply to the fan.


A modification has been added by you.
A relay has been put in place that has the coil of the relay connected to ground.
There is a manual switch that connects the positive supply to the other side of the coil.
The relay contacts are connected on one side to ground and on the other to another point.
The switch operates the relay and the fan runs.


The only explanation I can see for this working is if the "another point" is actually the connection from the ECU to the coil of the OEM relay that is labelled as 1-13 in the Elise wiring diagram you posted.


OK therefore I can only assume you have given incorrect information about the first modification.
The connection you have drawn in your original post as going from the rad fan to 87 of your relay must actually go from 87 of your relay to the ECU to coil cable.

Let's start from the basics this diagram shows a basic switch circuit and a basic relay circuit.
In the switch circuit closing the switch operates the bulb.
In the relay circuit closing the switch powers the coil of the relay by connecting it to negative (ground).
Powering the coil of the relay operates the relay contacts and connects the positive of the battery to the bulb and the bulb lights.



OK adding some labels to the relay diagram to match what you have in the car.
This is the OEM arrangement.
The temperature sensor is not shown but just causes the ECU to operate the switch shown as "ECU".
Point A is where you said you were connecting your modification, point B is where I think you have actually connected your modification.



The following is the first modification at the top and the timer relay at the bottom.
The top diagram is how I think you have connected your first modification and, if you have done it like this, then the bottom diagram is how I think your timer relay should be connected. (Where lines cross over they are not connected I just did not have enough space to keep them separate).

This accounts for you saying that you are grounding the fan and it operates.
If this is not enough for you to be able to work this out then I cannot give any more information that might help.

 

[mollydog]

Richard, I thank you very much for your effort very much appreciated

All I can say is, thank goodness now the law are keeping people like me away from mains electricity

After doing more research, the wire I'm connecting to is this one:

(not my image)



now this wire is on pin 86 of the factory fitted relay, meaning I am grounding the wire coming from the ECU to the relay "B" (RED) and not as I thought, grounding the wire out of the relay to the fan "A" (BLUE)


in effect doing what the ECU would do if/when it wants the fan on, ground the wire to pin 86, and this must be why I had to change a positive feed to a ground (negative) feed with my relay as is now

here is how I have the relay wired up at present to get ground feed from a positive feed



yellow & Black wired to earth, black grey trace to pos feed and white/black to pin 86 (B)

with this new information due to my massive error, hopefully it now all makes sense and be able to put me right

want to thank all of you for your help with my very bad diagrams

 

[guest119]

Ah, its a Rover engine? Therein lies your problem. A remnant from British Leyland days :shocked:.
I honestly thought you had a Lotus twin cam unit in there :shades_smile:.
Once again though, is your cooling system working properly?
Have you ever done a citric flush or ran it without the thermostat on a long run to see if it still gets too hot?

Boydy

 

[Richard Burns]

Thank goodness that is over, at least I was correct in post 3, the described set up would not work!

Just shows how important it is to get the correct information.

 

[Geordie Spark]

Ah, its a Rover engine? Therein lies your problem. A remnant from British Leyland days :shocked:.
I honestly thought you had a Lotus twin cam unit in there :shades_smile:.
Once again though, is your cooling system working properly?
Have you ever done a citric flush or ran it without the thermostat on a long run to see if it still gets too hot?

Boydy

Agreed ...... dreadful engine.

Chuck it out & drop a nice 3 litre V6 out of a Toyota Camry or Lexus in.

 

[mollydog]

yes a bit of a pig of an engine, but (was told) the Rover K series engine, per weight, it is/was pound for pound had more BHP per kilo than more engines of its time.

but sadly Rover were penny pinching and took lots of shortcuts, I have had 3 Rover cars (excluding this Elise) which had the K series engine in and they all developed head gasket failure, the MG TF we bought from new , regular servicing by main dealer looked after it never thrashing it, hit just 39,000 miles got HGF

so this is the reason I am making this effort, trying to prevent hot spots at the engine head by trying to keep the coolant temp as even as possible (when in traffic jams in Italy)

was told one of the causes of HGF (apart from other design faults) is where Rover placed the thermostat, hot coolant leaves the hot engine going to the rad at the front then the stat opens but as its on the return from the rad very cold coolant hits the very hot engine

you get expansion and contraction every few seconds as thats the way the coolant system on the engine is laid out, rapid change in engine temp that in time is going to cause the head gasket to expand and contract in rapid succession getting HGF, I've fitted a remote PRRT and hope this will help 70% and having the rad fan override will help in traffic jams

now I've been able to gather all the facts to the layout, is there a way that my timer/relay can be wire in to work?

 

[mollydog]

the newer Elise's do have the 6 gear ZZ Toyota engines and have been told they are chalk & cheese, far far better than the Rover K series with more BHP

 

[mollydog]

Richard, is there a way I could get my timer still to work with the setup?

 

[Richard Burns]

Richard, is there a way I could get my timer still to work with the setup?

Yes post 32 last diagram, bottom diagram; just put in a 3 A fuse on the positive to the timer relay coil (pos+), the rest of the circuit is protected by the original fuse.

 

[mollydog]

Thank you Richard for this

I'll be attempting this next week and post on here how I get on, many many thanks for this.

thank goodness there are laws now keeping people like me away from home electrics

 

[clydey]

yes diagram works perfectly
my only concern is the ecu switch
normally ecu use darlington transistors to switch loads (high/low)
the switch shows (open/closed)
my concern is the forced voltage on the darlington output (if indeed used) destroying the ecu
cheers

 

[mollydog]

Clydey, thank you for this bit of info, other that have wired it (like I had before) haven't heard any problems, but to be on the safe side would fitting a diode at location "C" solve/prevent the risk?

 

[clydey]

this is what i would recommend
introduce another bosch relay (same as original they come as 4 and 5 pins) choose 5 pin
call this relay 3
wire pin 86 of orignal relay to pin 86 of this relay
wire pin 85 of original relay to pin 85 of this relay
this then puts these two relays in parallel and when one energises so does the other
now open the output wire coming out of the ecu ( c) on your diagram (ie cut the wire so that you have two ends to work with)
put one end (any end) of the cut wire onto pin 30 relay 3
put the other end of the cut wire onto pin 87a of relay 3
---------------------------------------------------------
this results in a normal path when the relay is unenergised for the ecu output
and open circuits the output of the ecu when you
press your momentary button for the duration of time set by your timer relay
thus avoiding a conflict of voltages
cheers

 

[mollydog]

Thank you, Clydey for this, I think I have got it what you're saying, when I get home I'll do a diagram to show you to be sure I've got it right

many thanks for this further help