Hey,
I've run into a little dilemma; I would like to run a elctronic water temp sensor but the ecu gets the water temp from this sensor as well, if i was to hook up the guage a well would this change the reading the ECU is getting because the resistance would drop, or would it not matter???

Any ideas??

Cheers
Damo

Depends ... it could cause a voltage drop at the sensor and upset the ECU. If the new Guage has a high-resistance sensor circuit it won't be a problem.

You could also just put a second water temp sensor in.

Generally you only need to worry about the Oxygen Sensor. For example, if you use a voltmeter on this while the engine is running, the meter should have 20 Megaohm resistance (most voltmeters don't meet this).

(i was gonna post this last nite but my net connection died - so here it is)
shouldn't matter, although if you are concerned you can hook up the 2nd output on the thermo switch into a relay, to then power your dash guage. if your guage needs a 12volt rail, u should use a relay to minimize the possibility of any resistance. also the ecu should be powered from elsewhere, rather than directly from the water temp switch so it shouldnt be a worry.

this website has lots of demonstration relay setups. very handy for the interested garage sparky. (who doesnt have a welder)
http://www.the12volt.com/relays/relays.asp

i am more thinking, is the temp sensor of the correct resistance range for both the ecu and guage to read correctly on their own?
To be 100% certain that neither the ecu or guage send any feedback to each other you simply require to place a diode inline with the signal wire from the sensor to both the ecu and guage. ( that means 2 diodes)
Evilism you are talking about a thermo switch which is used to trigger a fan etc. Demojob is refering to a temp sensor which is used to send a reference signal to a temp guage or ecu, to accuratly measure varying engine temps

If you have effectively two guages trying to read, or pass current, through the same sensor won't this throw both of them out as the amount of current allowed to pass through the resistor(temp sensor) at any time is constant, therefore the guages will only read a fraction of the current each passing through the resistor?