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Re: 74 gmc c3500 need engine wiring diagram so I can hook...
All you need is to find the temp sending switch, which is somewhere in the water jacket (usually near the thermostat housing or in the intake manifold) and run a wire from it to the gauge in the dash.
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temp gauges run of sender units not sensors and have only one wire to them sensors on the other hand have 4 wires to them and communicate with the ECM and have nothing to do with the temp gauge
Try taking the wire of the temp sender unit and touching the engine and see if the gauge goes up to hot. If so then replace the temperature sender unit ( different to the sensor unit)
Not exactly. The check gauge warning light is on because the temp gauge is reading hot. Does the temp gauge read hot as soon as you turn the key switch on, or not until the engine as run for a few minutes ? If it reads hot without the engine being started, there may be a short in the wiring or the sensor may have failed.
To review, you have two temp sensors, one for the gauge on the dash and one for the computer. If you unplug the sensor for the computer the reading will be minus 30 degrees or over 300 which will make it very hard to start. Unplugging the sensor for the gauge would have no effect on the computer. According to the wiring diagram, the wire for the temp gauge is green, and the wires for the temp sensor for the computer are yellow and black.
you might want to check the wires going to the temperature sensor on the engine make sure it hasnt rubbed the protective coating off, this can give you a false reading, the safest way is to put a manual gauge in place of the temperature sensor and run engine to make sure the engine is not overheating. You can pick up a cheap manual temp gauge at your local parts store and install the temperature probe into the hole where the temp sensor was located and run the engine. It sounds like you have a guage malfunction. But is better to be safe than sorry.
On the intake manifold,toward the front. It's got 2 wires to it. That's the one for the cpu & the other has one wire & is usually in the driver's side head. That controls the temp guage.
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