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My pride and joy (auto-hobby wise) is a 65 C10 LWB, 400SB/t5. Starts and runs great, but recently, with demand on elec system, the ammeter pegs to right. Running or not, hit brake, headlights, fan, blinks all send ammeter to peg right. This to me seems like over charging and I don't know why it is doing it. I've had the instrument cluster out to work on temp gauge and recently replaced the starter. What will cause this and what should I check?

My truck is over charging due to a mis-set voltage regulator

Ok, I was thinking more along the lines of a short somewhere. Would a bad voltage regulator make the ammeter peg when the alternator isn't running?

Ampmeter pegging to the charge side with a short doesn't sound right. So more info is needed...what wires if any did you take loose? Do you have a way to measure the current with say a clip-on ampmeter? If so you can check if the meter has gone bad. WAG, did you hook the battery up backwards? Get back to us.

Reading amperage (w/ clamp-on amp meter) in wire going from alternator to starter hot post is 1.7 w/ normal load. Turned on head lights and amperage reading same place increased to 1.9 - I thought the alternator would put out more like 80-100(?). Checked voltage at alternator and got 14.4 and 14.5 V. Still don't know about the amp reading I got and the still high ammeter gauge w/ load.

Find out if meter has internal shunt - ie connected in line
OR
has external shunt.

IF internal run a known current thru it and check reading
IF external run a 50 mV signal to it and check reading --should be full scale.

From sparce info provided I tend to think bad meter or bad shunt

Dan Bentler

Voltage 14.4/14.5 is good. Check it at battery posts also. If that also reads 14.4/14.5 , your truck is charging correctly. That means the ammeter or circuit is faulty.

You still have not told us what if anything you disconnected in your temp gauge repair. Could you have reversed the leads to the ammeter? I don't know a '65 but was it built as a 6 volt and converted to 12? I also agree you need to look into the shunt thing. Also think that the output from the alternator is not correct.

Thanks for all the input. Here are replies to the last few posts. Lets see ... I'll investigate the meter and figure out what I don't know about the A readings. I bought the meter yesterday morning and am a little unfamiliar with it. I did check voltage at battery and it reads just slightly lower than readings at the alternator, still above 14V. I think the 65 was 12V to begin with so no conversion from 6. I disconnected everything from the cluster several times tying to chase down the faulty temp gauge (turns out I had two bad temp senders in a row - thanks autozone). Broke the oil pressure line once, tried to get the tach working(the cluster came out of a dump truck and came equipped w/ tach) So now the temp is working, ammeter?, tach not working yet, I may have fritzed the fuel gauge.

Hook up the ammeter with separate test wires, bypassing ALL stock wires and see if it works or not. Ammeters are fire starters, even with a shunt. Too many amps. Put in a voltmeter instead. Then you can read the 14.5 Volts from inside the truck. Some Voltmeters need to be calibrated to a good remote voltmeter by turning calibration screw or bending needle. Your charging system is charging properly as I already said.

Where is the shunt and and what does it look like?

A shunt is a wire/component for resistance, I believe in the sensing circuit. It is probably a brown wire with white stripe on your truck. Some look like a terminal block. Forces a per centage of the current to run thru the gauge. You need to get a schematic for your truck. 60-66 had different wiring systems for curtain years. There may be football shaped fuse holders in the ammeter circuit (small, hard to find) that you need to find that are probably blown. Check all fuses in fuse block also. You could have an open circuit from broken wire or blown fuse. Check to see if there is voltage at meter. One side of meter is batt hot, other is alt output. There may be a wire or two for the gauge light. Get educated on this stuff from internet search if you continue. Dozens of hits on 65 Chevy ammeter problems.

Try adding a ground wire to the inst cluster-sometimes paint, etc gets in the way of a good ground there, making gauges act wonky. The shunt is usually a small black wire with white tracer, one end is near the starter, one end near the horn relay-it senses the voltage diff and moves the needle.