I own a 1970 corvette 350/350 4 speed coupe with air. I am having trouble with the gauges. The temp gauge I do not think is working properly. The temp gauge does move but barely hafeway to the second notch on the gauge. I am getting power to the gauge. The gauge pegs left when I pull the wire off the sender and goes to hot when I ground it. The ohms reads the same from the sender through the wire to the gauge. It starts at 220 and lowers to around 150 when warm. I believe I should be getting more movement on the gauge?

The battery gauge does not move at all. The wire leading to the gauge has a voltage of 12 coming from both wires.

Are there any thoughts on these problems?

 

Temp gauges have problems if right temp sending unit is not installed (early Vettes take a special sender and many replacements are not correct calibration for proper gauge performance) also don't use sealer on threads to cylinder head, it can effect reading. Ammeter gauge is probably failed if no reading with voltage present. Roger, a poster on this forum has made some good references for bench testing gauges, maybe do a thread search for his excellent posts.

 

I agree, you need a temp sender with the following resistance to get the correct temp reading.
70 ohms =220*
90 ohms =200*
140 ohms =160*
250 ohms =120*
I've had good luck with a Wells TU5 or a BTW WT203 but they can be way off even out of a new box.

To bench test the battery gauge:
Connect a ground to the top post and just touch 12 volts to the bottom post - needle should deflect downward.
Connect the ground to the bottom post and just touch the top post - needle should deflect upward.

Hope that helps, Regards, Pete.

 

You don't have a "battery" gauge in the 1970 Corvette. You have an ammeter, which measures the about of 'charge' or 'discharge' from the battery. It is scaled in Amperes and should normally run close to the "0" mark if everything is working right with the alternator/charging system.

You will measure 12 volts (or a little more or less) at each of the meter input wires, because the gauge is actually a 'shunt' glavanometer...or a millivoltmeter with a built-in shunt resistance which is part of the C3 wiring harness. The meter is calibrated in Amps, but it is measuring the small voltage drop over a fixed length of wire in the main wiring harness. That voltage drop is proportional to the current flowing through that main wiring. If the battery is discharging, it goes negative; if the battery is charging, it goes positive.

To see if it works, just go out to the car and, with the engine OFF, turn on the headlights. The ammeter should should somewhere between 5-10 amp discharge. Then hit the bright light switch. The meter should show 10-15 amp discharge. Turn off the lights and start the car. Immediately after firing, the meter should show some discharge (10-20 amps or so) and that reading should slowly move toward "0" as the alternator recharges the battery {which lost charge during the use of the starter}. After a few minutes (driving is better than idling, as it recharges the battery faster), the battery should be fully charged and the meter should be back to a "0" reading.

If your meter works as described, there is nothing wrong with it.
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From your description of the temp meter, your problem is a 'bad' sender unit mounted in the left cylinder head. You need to find one that is meant for use with your year car, as these senders changed from year to year and the calibration is different. An 'incorrect' sender will provide readings to the temp gauge...but they will be badly in error. The gauge and wiring would appear to be operating as expected.