Ammeter revisited 1966

[Randy S.]

Thought I'd start a new thread re my inoperative battery meter.

Hasn't worked since I have owned the car for 10 years. I only get a small deflection when the headlights are on. My battery is 6 years old so I assume my charging system is working.

Here is what I have done a few years ago before I gave up.
Cluster rebuilder says gauge is Ok. I also did the AAA battery 1.5 volt flash test and got movement of the meter so I am ruling out the meter itself.

I cleaned the bulkhead connectors and I get voltage at both legs of the meter so no open circuits there. Check connections at horn relay

I read in the archives that the battery meter reads the voltage drop across the 10 ga red wire that runs from the solenoid B terminal to the alternator B terminal (then to the horn relay). I removed the connection at the solenoid and sandpapered the ring terminal where both the #10 and #18 black wire are terminated.

Today I took some voltage measurements

battery 12.7 volt at battery terminals (engine off)

With ammeter connector disconnected
12.38 volt to ground each leg ( eng off)
13.8 volt to ground each leg (engine at idle) maybe 13.7 with headlights on
This tells me no open circuit in either the #18 black wire to solenoid or the #18 B/W that goes to the horn relay

Leg to leg at ammeter connector
0 volt (eng off)
.03 volt (eng on)

Any ideas of where to check next?

[William C.]

Re: Ammeter revisited 1966

You are dealing with a very sensitive measurement here. The ammeter actually is a VERY sensitive Voltmeter that measures voltage drop across a 12 gauge wire. The condition of the connections at the firewall are 95% of the time where the problem lies. you might have inspected them, but that is not really enough for the function that the wire is performing. Clean and inspect, re-arch the tongue of the terminals on both sides of the connection and see if you get better results. You are dealing with a measurement in Millivolts, so you don't own a meter that will see the problem for you.

[Randy S.]

Re: Ammeter revisited 1966

Bill,

Thanks for the reply. I pulled the inner connector and tried re-arching the pins. I am obviously getting a connection based on my voltage reading but maybe too much resistance. No noticeable difference in battery reading.
I do see a problem with my connector. The top "loop" that retains the connector is worn round and I cannot get the connector to latch. I suspect that even though I have an electrical connection I cannot get enough pressure at the contacts to reduce the resistance.

I think as a test I may measure the resistance of 8 to 10 ft of 18ga wire and compare that to the resistance of the two 18ga battery leads thru the firewall connector.

Randy

[Rich G.]

Re: Ammeter revisited 1966

My 66 is the same. My first battery lasted seven years, so guess the charging system works. I posted the same question a few years ago and got responses like " my 66 has been like that since new"

I have not done the research you have. My 68 ammeter works the way you would expect it should. Is the circuit different in 66?

Rich

[William C.]

Re: Ammeter revisited 1966

I haven't looked at the circuitry for a '68, but the '63-67 system actually measures the voltage drop across both ends of a wire to infer amperage. It is VERY sensitive to any extra resistance in the connections, and the usual culprit in problems is the connection between the IP and the engine compartment at the back of the fuseblock. If you are going to measure the resistance you will need an instrument that reads Milliohms.

[Randy S.]

Re: Ammeter revisited 1966

You are dealing with a very sensitive measurement here. The ammeter actually is a VERY sensitive Voltmeter that measures voltage drop across a 12 gauge wire. The condition of the connections at the firewall are 95% of the time where the problem lies. you might have inspected them, but that is not really enough for the function that the wire is performing. Clean and inspect, re-arch the tongue of the terminals on both sides of the connection and see if you get better results. You are dealing with a measurement in Millivolts, so you don't own a meter that will see the problem for you.

Bill and others,

Ok I borrowed a mechanics Snap On multimeter

I measured 10 ft of 18ga brand new stranded wire and got .3 ohm. According to tables on internet should be about .06 ohms so I guess the difference is the meter leads. I assume the wire run in the engine harness is about 10ft. I measured the 18ga black wire with white tracer that goes from battery meter to horn relay and got .7 ohm. I measured with my own meter and got .7 ohm. So thru the firewall connector it appears to add about .4 ohm to the circuit. I did not measure the solid black 18ga. side as my leads are not long enough to reach to solenoid battery terminal.

So do I have a resistance problem at the firewall connector?

[Joe R.]

Re: Ammeter revisited 1966

So do I have a resistance problem at the firewall connector?

Randy,

It sounds to me like you do.

Joe

[Thomas H.]

Re: Ammeter revisited 1966

Bill and others,

Ok I borrowed a mechanics Snap On multimeter

I measured 10 ft of 18ga brand new stranded wire and got .3 ohm. According to tables on internet should be about .06 ohms so I guess the difference is the meter leads. I assume the wire run in the engine harness is about 10ft. I measured the 18ga black wire with white tracer that goes from battery meter to horn relay and got .7 ohm. I measured with my own meter and got .7 ohm. So thru the firewall connector it appears to add about .4 ohm to the circuit. I did not measure the solid black 18ga. side as my leads are not long enough to reach to solenoid battery terminal.

So do I have a resistance problem at the firewall connector?

You need to short the meter leads together and subtract that reading from your measurement. Sometimes the meter leads add up to 0.3 ohms.
Either way, it looks like you have about 0.4 ohms in your harness. Taking the connectors apart and cleaning them with some contact cleaner may help.

Tom

[Randy S.]

Re: Ammeter revisited 1966

Either way, it looks like you have about 0.4 ohms in your harness. Taking the connectors apart and cleaning them with some contact cleaner may help.

Tom

Spent yesterday and today cleaning the firewall connector contacts and re arching the pins, contact cleaner, dielectric grease, etc.. Reconnected and measured the resistance at the battery meter connector. Got .20 ohm in each 18ga lead ( down from .40 ohm). The battery gauge moves a little more than before but not sure what should be normal. Minimal deflection since I have owned the car. Starting the car is about 5 amp discharge.

I would like to know what the resistance value should be for each of these 18 ga battery leads. Anybody got a harness laying around or take a measurement?

How much should my battery gauge deflect on engine startup?

Thanks to all who responded, I am getting there!!


Randy