Temp gauge issue with Scout 800

[scoutzilla]

Have a 69 Scout 800, had a stock temp gauge that did not work when I bought it (in fact none of them did) I replaced them all with autometer gauges, I attached the sender to the base of the housing where the thermostat is, now when I start the truck, as the engine is warming up, the needle on the gauge rises as you would expect, but never stops, it keeps rising until it pegs, and then stays there.
The cooling system is in good working order, and the engine is obviously not overheating, it has a new thermostat and fresh coolant, the only thing that I changed is I capped off the heater hoses at the water pump and the water neck where I placed the new sender....did capping these hoses off create an issue? Or did I get a defective gauge? Can't figure this out...

 

[Scoutboy74]

The stock gauges are fed a stepped down voltage via a little device called a constant voltage regulator. Since all the gauges were misbehaving, its possible that the cvr was malfunctioning or perhaps there was an issue within the associated circuitry. Some methodical, yet fairly straight forward diagnostics would be required to determine the exact cause.
The aftermarket gauges require full voltage and its possible that they May also be designed to function on a different resistance range than the stock gauges and individual senders were designed for. Not being familiar with the product, I can't offer any more than random speculation there. The stock gauges and senders operate on a 10 to 73 ohm range with one end of the spectrum registering a low gauge reading and the other end registering high. Suffice it to say, there is more involved in these gauges and sending units than just plugging them in and hoping they work. Stuff has to match and be correct.

 

[Tahoedonner]

You either have a bad ground at the gauge or your sender is not compatible with the gauge. I bought a new auto meter specific sender when I replaced my gauges.