tylerwerrin

Hi guys,

Does anyone have a low coolant warning lamp circuit I can take a peek at? I'm trying to figure out how to wire it up to my jag's dash -- I have the sensor as part of the coolant tank -- it's from a 99 Malibu (the sensor is built in) but the power ratings are the same (+5v i believe) but I don't know how it factors into the dash -- shbox's site says it doesn't report to the PCM, so that means it must be a simple fix --

From looking at cars in the junkyard, the sensor is grounded at the same ground point for the dual electric fans -- but where does the +5 voltage come from? or is my voltage wrong?

The wire indicated on the c205 connector is patched into the jaguar's low coolant light in the dash... I think in a stock application, the low coolant switch is powered by a wire in the Fan harness, but since I don't have the stock harness... Does the switch just get operated by simple voltage? If so I can just tap into another wire for the feed -- i'm just not sure exactly how it functions.

Any ideas?

bobdec

Tyler, I know on a LT1 setup the low coolant sensor is just a switch, 50,000 ohms when submerged in coolant and close to 0 ohms when dry. If the '99 Malibu is similar you could use any voltage bulb preferably +12 v ignition on. Tie one bulb end to +12 ignition and the bulb ground to the switch. You can verify the sensor operation with an ohmmeter, but that would require draining coolant below the sensor to see how the sensor operates when dry. ( PS: ever get you speedometer working ???)

tylerwerrin

Hi bob!

Yep, I got the speedo working -- it was a combination of adjusting the ratios in TunerCats and adjusting the pulses from the converter box to be read accurately on the speedo. My next project is getting the Trip Computer in the Jag to accurately read the instant fuel consumption and MPG functions from the V8 (i've found a few writeups, but they are very complex...)

I know the wire that i have patched to the low coolant bulb is yellow/black -- it enters through the c205 connector i believe (at least that's what its listed as for the Caprice). I have one end connected to the light in the jag's dash, but the other end isn't connected to anything. I suppose i could just run a quick splice under the dash to test, but do you know where the yellow/black wire terminates in the harness? I need to find a diagram so I can trace it to where it emerges in the harness... i suspect it's not part of the main engine harness, but a body harness. Not sure though...

Injuneer

What could be a fairly simple circuit is complicated by a "latching" feature built into the low coolant latching module (93-95) or the body control module (96-97). The latching feature prevents the light from flickering. Once the level has been low for more than a few seconds, the "latch" keeps the light on for the rest of the trip, even if the level sensor picks up the correct level.

I'm looking for the diagram in my 94 manual, and also have a 98 manual that includes the BCM. If I can find it, I'll post it.

tylerwerrin

i checked my wiring diagram for the caprice harness, it looks like it goes from the c205 connector, to a c103 connector to the switch and then is grounded at the same ground point as the electric fans.

However, I have no idea where the c103 connector is -- it's not cross referenceable in the connector faces section of the manual!

Where does the mysterious yellow/black wire go in the harness? That will tell me where i can patch into...

bobdec

Tyler, probably have to wait for Rob to see if he has a caprice harness diagram. My F-body harness is different.. After looking at Rob's post I looked harder on my wire diagram and the ground side of the indicator lamp has a a splice, one wire goes to the low coolant switch in the radiator, and the other wire goes to a Retained Accessory Power (RAP) module. (Lean something every day). Looks like my RAP has an internal electrical circuit latch that keeps the wire grounded till the key is turned off. So as Rob said it prevents the lamp from blinking and holds the indicator on so the driver is forced to see it. . Unless you have something in the jag similiar to the RAP or Body Control Module (BCM), straight wiring your indicator will blink on and off if your coolant gets low and you drive around corners.. My connector numbers do not match yours, so I cant help there, but my color is all yel/black from the dash lamp ground side to the switch and also yel/blk to the my latch circuit in the RAP, its black from the other side of the low coolant switch to a ground distribution splice.

tylerwerrin

Hi Bob,

I had a feeling that the c205 wouldn't exist for F-bodies... its good that the wire color is the same though, maybe that's enough information to track it down.

I don't think I have a RAP module (the jag certainly doesn't) -- I looked through the manual a bit more and I found that the yellow/black wire comes out of a connector that has wire hookups to the fan harness. I confirmed this by checking under the hood, but when I probed the yellow/black wire with the key on, I didn't get any voltage whatsoever. I tried "faking" the circuit by using a spare low coolant sensor, hooked into the plug, which was spliced into the yellow/black wire in the harness, and grounded the other side to the neg battery post, but the light still failed to go out.

Finally, to make sure the wire wasnt frayed or messed up somehow, i probed the voltage at the c205 connector itself -- and still no dice. The shop manual doesn't say that it's looking for 12v but if the light goes on, there has to be some kind of voltage right?