Water Temp Gauge Problem

[blueoval1]

On my 89 Cobra 4.3L I can't get the water temp gauge to work. I replaced the sending unit first with no luck. Then I replaced the gauge , still no luck. I am wondering if either I have the wrong sending unit for the gauge , or I have a wiring issue. Any way to test the wiring? Is there a generic wiring scematic for water temp gauges? Any ideas about the sending unit having to match the gauge?
Thanks!

 

[Silvertip]

Re: Water Temp Gauge Problem

Lets see, you have a new sender and a new gauge! That pretty much leaves wiring as the issue right?? Here is a fuel gauge wiring diagram. Pretend the fuel sender is a temp sender, and that the fuel gauge is a temp gauge -- the net result is the same. It all works on resistance. Again -- knowing what we are working on would help, knowing what resistance is of the temp sender you bought (or a part number) would help as well. For testing, you need 12V on the "I" ignition terminal on the gauge when the key is in the RUN position. The ground "G" terminal on the gauge must be connected to ground, and the "S" sender wire must be connected to the sender. If the gauge has a light, it can be connected to the light terminal on any of the other gauges. Grounding the "S" terminal should peg the needle to the HOT end of the gauge. Lastly, if you used about eight wraps of teflon tape to seal the threads you prevented the sender from making a ground connection so the gauge can't work.

 

[blueoval1]

Re: Water Temp Gauge Problem

Yeah Silver , I know I should have given you a part # but I did it at the begining of the season and I wasn't smart enough to save the package to the sending unit:redface:

The gauge is a Faria Coral series #13004.
Thanks for the diagram. I am not worth a sh_t at visualizing wiring layouts
I don't know if that gauge # could tell you what sender it takes or not. I can't seem to find any info on the net anywhere.
Thanks again!

 

[Chris1956]

Re: Water Temp Gauge Problem

There are two different types of senders for water temp. Both are used on I/Os. One sender grounds when the motor overheats, activating a horn. (just like the idiot light in a car) The other type of sender changes resistance to ground as the temperature changes. This is the one to be used with a gauge. You might be able to look up the part number of the sender (if it is stamped on it) and see if it is for a gauge.

BTW - Different gauges use different senders as well. The resistance range of the sender needs to be matched to the gauge.

 

[Silvertip]

Re: Water Temp Gauge Problem

Wiring on a boat doesn't get very complicated. I would guess if there was a 100 foot piece of rope laying on the ground you could follow it from one end to the other could you not? Well -- think of the wire that runs from the sender on the engine to the "S" terminal on the gauge as about a 15 foot piece of rope. It has a color so you simply follow it and make sure its connected (tightly) on both ends and not broken anywhere in between. You didn't answer the question about the teflon tape on the threads of the sender. If you used it, remove it and use pipe sealer so the the shell of the sender can make connection with the engine block. Now make the other tests using a test light and ohm meter. You need 12 volts on the "I" terminal and ground on the ground terminal. You are missing one of these.

 

[blueoval1]

Re: Water Temp Gauge Problem

Thanks for the help guys! Silver , I read up on the teflon tape problem here in the forums earlier. I was hoping that was it , but it wasn't.
I wll start chasing wires and checking for power/resistence. Going to have to check it out this weekend though. It's snowing like mad here.
I will report the outcome
Thanks again!

 

[Boatin Bob]

Re: Water Temp Gauge Problem

If you have power and a good ground at the gauge I would use a contiuity tester (ohm meter), put one end on the wire at the sender and the other end at the sender wire at the gauge (disconnect it from the gauge) you may have to extend your leads, not sure how big the boat is. If you don't get continuity the first place I would check is the big black round Canon connector at the upper rear of the engine, all the dash wires from the engine go through there, sometime you get corrosion on those pins.

 

[blueoval1]

Re: Water Temp Gauge Problem

Good idea Bob! I'll check it out and clean it up.
Thanks!!