gas and temp gauge

[65truckowner]

I got my 65 c10 running today. I have a new wiring harness behind the dash and have redone the wires under the hood. My question is the gas gauge and temp gauge only move up to the empty mark and the first mark on the temp when I have the key on or the engine is running. I have a new sending unit in the tank as well. I unhooked the wire from the sending unit to see if the gauge would peg out. It just moved to empty. What is causing this. Also my new alternator is not charging. The amp gauge will not move at all.

[Pitpig]

Make sure sender is 90 ohm. I had to ground sender to frame to get it to work

[65truckowner]

I unhooked the sending unit and the gauge did the same thing. Both gauges are doing the same things

[The Rocknrod]

65 sender would be 30 ohm correct?

[65truckowner]

I dont think it is the sender. I can unhook the sender wire and the gauge still just goes up to empty.

[ACK]

Did any of the gauges work properly before rewiring or was everything already toast? I've read '65 & '66 is when Chevy started switching over the OHMs on the sending units, if you still have the original sending unit, see if there's a number stamped on it and do a cross reference; if it's gone, I suggest the following. With the engine off, read the OHMs at the sending unit terminals, the number should reflect the amount of gas in the tank, now check the OHMs at the gauge. If they match, the problem is likely the wrong sending unit or a bad fuel gauge.

Is a multimeter saying the alternator is not working or the gauge? If a multimeter is saying it's not putting out the right voltage, take it out and have it bench tested. If it's the gauge, I would test the wires at the gauge with a multimeter. If the readings good, I would suspect the gauge is bad.

[65truckowner]

I restored the truck. I have no idea if anything worked or not. But on a normal working gas gauge if you take the wire off of the sending unit stud then turn on the key should the gas gauge go all the way to full? I have tested gauges in the past like this. IF this is correct mine gauge does not do this it only goes up to empty when the wire at the sender stud is disconnected.

[ACK]

Originally Posted by 65truckowner

I restored the truck. I have no idea if anything worked or not. But on a normal working gas gauge if you take the wire off of the sending unit stud then turn on the key should the gas gauge go all the way to full? I have tested gauges in the past like this. IF this is correct mine gauge does not do this it only goes up to empty when the wire at the sender stud is disconnected.

Yes, pulling it should send it to full and touching it to a ground should bury it on empty.

[65truckowner]

Ok I did both and the gauge does nothing past empty mark. I have power at the fuse if I unplug the sending unit wire at the fuse box. One I plug the wire back in I loose power at the fuse

[ACK]

Originally Posted by 65truckowner

Ok I did both and the gauge does nothing past empty mark. I have power at the fuse if I unplug the sending unit wire at the fuse box. One I plug the wire back in I loose power at the fuse

If you don't have a multimeter, I'm strongly recommending to purchase one and testing the fuse block and wiring to see what's good and what isn't. Also check the instrument cluster connector, make sure the terminals are clean and the connection is solid. Good luck.

[65truckowner]

I have one

[65truckowner]

I did some testing today. I pulled the sender out of the tank and used my meter to check ohms. At full it was 30 then went down as I moved the float down. Then I checked at the fuse and had 12 volts. I turned my meter to continuity and touched the two blades on the back of the gauge I did not have continuity, is this right? Also when I had the sender out of the tank I hooked up the wire to the stud and moved the float up and down and the gauge did not move from the first mark on the gauge.

[ACK]

Originally Posted by 65truckowner

I did some testing today. I pulled the sender out of the tank and used my meter to check ohms. At full it was 30 then went down as I moved the float down. Then I checked at the fuse and had 12 volts. I turned my meter to continuity and touched the two blades on the back of the gauge I did not have continuity, is this right? Also when I had the sender out of the tank I hooked up the wire to the stud and moved the float up and down and the gauge did not move from the first mark on the gauge.

This is getting a tad beyond my knowledge. If the gas gauge is 90 OHM, which is very possible for a '65, the 30 OHM sending unit will only tell the gauge it's no more than 1/3 full.

Here's some multimeter data from my C10 30 OHM gas gauge that may or may not help:

OHM set to 2000, readings taken from the brass spades and not the nuts due to wide fluctuation in readings:
Resistance between the 2 spades is 40
Resistance between left spade and bottom bar is between 24 - 35
Resistance between right spade and bottom bar is between 5 - 17
Resistance between ground (gauge casing) and bottom bar is between 56 - 66

Resistance tone was given between the bar on the bottom and the right spade, also the left spade and simultaneous contact with both the bar on the bottom and gauge casing; no tone between the 2 spades.

Keep us posted on your travels. BTW, is it me or does the back of the gauge look kinda like a pissed off muppet.