1990 silouette 3.1 v-6 looking for the temp switch, replaced temp sensor, fan relay and fan ( fan tests good and runs independently) still won't come on. Temp gauge is jumpy and showing 240-260. replaced thermostat and water pump. Radiator holding pressure but does not seem like its at 260 I'd estimate 190. Gauge is wrong but I can't find it to replace it.

wow, no year stated. 1972?
first year with codes, 1988/99! (most cars)
help for what?
what do you want to fix first ?, seems its a large list.
the fan?
its all here.
alldata.com

i could offer real accurate help but no year stated. sigh.

to me , sounds like you lost ground to the sensors
and some years have an ECU 5v output that runs sensors
that can DIE. (with brand new sensors)
sensors need power to work, so we use a voltmeter to test live circuits, this shows me exactly why its failing.
(3 causes)

This is normally the fan relay which is fried. It can be that the fan is pulling too much current , which causes the relay to fry. It is a good thing to change both fan and relay.
If the sensor is faulty, then you won t see coolant temperature on the instrument panel.

A mechanic would use a scanner to check the engine temp sensor.
The temp sensor tells the computer what the engine temp is and the computer activates the fan relay when the temp reaches about 230 degrees.
Since you said relay I am assuming your Jeep has an electric radiator fan.

Need to know some specifics for a specifis answer.
To answer in general, Sounds as if you replaced the correct computer temp sensor (it would have a voltage reference signal) and not the gauge sender. The temp may need to reach 235 degrees or so to kick the fan on. Too me that is way too high. But running at a higher temp normally lowers emissions and I think that is the reason for the high temp to kick on a fan.

With a scanner you can see what the temp sensor is reading and when there is a fan request from the computer. Not everyone keeps a scanner for home use.
Do you have A/C and does the fan ever kick on when the A/C is on?

You can try this,
Go to your factory fan relay and figure which is the ground signal wire (the ECM sends a ground signal to trigger the relay. Early wire such as in my 89 IROC is a green with white stripe). Ground this wire with the key on. Does the fan come on?

If the fan comes on, look at the cylinder heads between the exhaust ports. The right side may have a pipe plug towards the rear. Left side it would be up front.
If there is a pipe plug then there is a provision to add a low temp fan switch. Search SummitRacing.com (or another source) for a low temp fan switch. Hypertech makes some. Install that into the port where the pipe plug is (careful of thread sealant as it can interfere with a good ground it needs). Connect the wire from the low temp switch to the ground wire of the relay. You can use a center tap as all you're doing is adding a ground (thats not like something that will draw current which you don't want to do).
This way you have a low temp switch to send a ground signal to the relay and still have the factory computer circuit.

You can get free wire diagrams from autozone.com in the repair section. This way you can look up your specifuc vehicle and see what wires do what and which would be the ground from the ECM.

CHECK MODE RELAY IF BOTH RELAYS GOOD YOU CAN CHECK RELAY BY REMOVING IT FROM FUSE BOX HOOK RELAY TERMINAL 85 TO BATTERY POSITIVE AND GROUND TERMINAL 86 IF CLICKS RELAY GOOD. IF RELAY GETTING POWER GOOD AND THE 30 AMP COOLING FAN FUSE OKAY.EITHER THERE IS A SHORT IN COOLING FAN WIRING OR THE PCM HAS FAILED.THE PCM HAS LOST OR COMMAND RUN CIRCUIT IN PCM SHORTED OUT DUE TO PCM FAILURE.LET DEALERSHIP OR GARAGE USE DIAGNOSTIC EQUIPMENT TO ACTIVATE THE PCM SEE IF IT HAS FAILED.DONT SPEND MONEY ON NEW PCM COULD BE SHORT IN THE WIRING CIRCUIT

Circuit is fairly simple. First check the 3 amp relay fuse. the fuse is probably in the engine compartment relay box along with the relays Assuming the fuse is good, with the engine hot and running, interrogate the relay #2 socket with a test light or voltmeter to see if you are getting the ground signal from the temp switch. To do this, connect one test lead to battery positive and the other lead to each terminal in the socket. If there is no ground signal there, your test light will not come on bright (it may come on dim for some of the terminals). If the ground signal is absent, replace the switch. If the signal is present, the relay should click when pushed back into the socket. If the relay doesn't click, either the relay is bad or the wiring from the fuse is bad. These are the likely causes. If this doesn't solve it for you, please get back to me.

The thermostat on the radiator opens by heat automatically. The fan switch is run by the Engine temp Sensor and the ECM. If your fan is not running it is most likely a problem with the fan or the Temp sensor, I would look at the fan first.

On a vehicle this age, it is likely that the fans themselves have worn out. Test the fans by running battery power directly to the positive contact. If they start, they are OK. On 4.3 motors, there is also a seperate temp sensor to signal the fans, usually called a fan switch. I believe it operates independent of the ECM. Another possible culprit is a bad ground at the fans or even a loose or corroded negative battery cable.

If you have changed out the relay, and disconnected the temp cooling sensor, make sure you have replaced the correct relay; I believe there is one bank of four relays located by the passenger side head lamp. If the fan is running continuously, then I would say the relay is stuck in the closed position, resulting in completing the electrical circuit, powering the fan. Have the new relay tested. You can find a wiring schematic in the Hanes manual for your make and model.

the cooling fans are run by a relay it's located in the junction box. check this. there is also a thermoatic sensor located near the fans next to radiator. the fans should free spin when the engine is off this is a good indiacator that it's not the fan themselves. if the relay checks out(run engine and switch the fan relay with the a/c clutch relay when the engine reaches 180 degrees you will feel the upper radiator hose get hot the fans will turn on a short time later iof they don't it's the temp sensor near the radiator if they do it's a bad relay...please rate this thanks