Ammeter Help
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
Ammeter Help
I recently replaced the line to my oil pressure gauge and now the ammeter doesn't work. It's operation seemed erratic before but now the needle is pegged way past the +40 mark (at about the 4 o'clock position).
As I understand it, the ammeter measures the voltage drop across a known resistance portion of the charging circuit. So, I checked the leads connected to the back and I am getting good voltage to each. I also checked that the battery is being charged which it is.
I am assuming the gauge was going bad and my banging it around while removing and installing the gauge cluster finished it off. Sound reasoning or should I be checking other parts of the circuit?
Thanks
DC
As I understand it, the ammeter measures the voltage drop across a known resistance portion of the charging circuit. So, I checked the leads connected to the back and I am getting good voltage to each. I also checked that the battery is being charged which it is.
I am assuming the gauge was going bad and my banging it around while removing and installing the gauge cluster finished it off. Sound reasoning or should I be checking other parts of the circuit?
Thanks
DC
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
Yes the Ammeter is effectively spliced in on a hot line between the starter and the horn relay. Does it stay pegged even when the switch is on/off/car is running etc? Did you possibly reverse the polarity of the connector at the gauge?
I have a 73 wiring chart pdf. If you PM me with your email I will send you a copy.
-patrick
I have a 73 wiring chart pdf. If you PM me with your email I will send you a copy.
-patrick
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
Wiring?
The Red#10 from the horn relay down to the starter motor is the wire that may be the problem. You should be able to find two orange "fuse links", one at the horn relay and one along the Red wire along the firewall. These two orange fuse-links tie the "voltage" generated along this length of Red wire to the ammeter. If current is flowing along this wire towards the starter, and on to the battery (from the alternator) the ammeter shows "Charging". If the current is flowing from the battery/starter to the horn relay the meter shows "Discharge" . I'd guess something happened to this wire, and I'd fix it fast because the ammeter appears to be getting an "overload".
Andy
Andy
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
Yes the Ammeter is effectively spliced in on a hot line between the starter and the horn relay. Does it stay pegged even when the switch is on/off/car is running etc? Did you possibly reverse the polarity of the connector at the gauge?
I have a 73 wiring chart pdf. If you PM me with your email I will send you a copy.
-patrick
I have a 73 wiring chart pdf. If you PM me with your email I will send you a copy.
-patrick
Thanks for the chart offer. Will PM you with my email address.
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
The Red#10 from the horn relay down to the starter motor is the wire that may be the problem. You should be able to find two orange "fuse links", one at the horn relay and one along the Red wire along the firewall. These two orange fuse-links tie the "voltage" generated along this length of Red wire to the ammeter. If current is flowing along this wire towards the starter, and on to the battery (from the alternator) the ammeter shows "Charging". If the current is flowing from the battery/starter to the horn relay the meter shows "Discharge" . I'd guess something happened to this wire, and I'd fix it fast because the ammeter appears to be getting an "overload".
Andy
Andy
Doesn't this mean I could disconnect the ammeter and if my battery is still charging properly, the red #10 wire and thus the charging circuit is okay? If so, would that not confirm a bad gauge?
I will check this first thing tomorrow when I get off work.
Where is the horn relay located?
Thanks,
DC
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
Tonight I disconnected the plug at the back of the ammeter and then checked to see if the battery was charging which it was. That tells me the charging circuit is still intact. Even so, I traced the wiring from the starter to the horn relay. Didn't find anything out of the ordinary.
Bubba was present and accounted for. The stud on the horn relay was stripped and Bubba cross threaded a couple of metric nuts to make the connection tight.
I've concluded the ammeter must be bad. I'll check for sure next time I get a chance to pull the gauge cluster.
Thanks for all the help.
DC
Bubba was present and accounted for. The stud on the horn relay was stripped and Bubba cross threaded a couple of metric nuts to make the connection tight.
I've concluded the ammeter must be bad. I'll check for sure next time I get a chance to pull the gauge cluster.
Thanks for all the help.
DC
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I've never known of an ammeter to fail and still indicate a 'high charge' condition. If the meter mechanism fails, it normally just reads "0". I'm thinking that your charging system is stuck in the charge mode...or [more likely] you accidentely caused some kind of significant short when you were working in there, and the charging system is constantly working to keep up with it. For instance, the power wire for the cigarette lighter got pinched and has a small area of the wire shorting to ground. Since it is pinched...and not loose....it doesn't really cause any arcing and that wire is capable of carrying significant amps. I'm just having trouble coming up with another scenario where the ammeter shows high charge rate all the time. 
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
DC
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
I've never known of an ammeter to fail and still indicate a 'high charge' condition. If the meter mechanism fails, it normally just reads "0". I'm thinking that your charging system is stuck in the charge mode...or [more likely] you accidentely caused some kind of significant short when you were working in there, and the charging system is constantly working to keep up with it. For instance, the power wire for the cigarette lighter got pinched and has a small area of the wire shorting to ground. Since it is pinched...and not loose....it doesn't really cause any arcing and that wire is capable of carrying significant amps. I'm just having trouble coming up with another scenario where the ammeter shows high charge rate all the time.
The alternator (new by previous owner right before I purchased the car a few weeks ago) output is weak at idle but picks up at about 1000 RPM. A voltage meter on the battery read about 12.6 volts with ignition off, then showed 12.8V with the engine idling, then 14.5V once RPMs were around 1000. This was the same whether the wiring was connected to the ammeter or not.
As far as causing a short, I disconnected the battery for most of the work but I did tilt the gauge cluster out one last time to check for oil leaks after I had let the engine run a bit.
DC
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Gauge is probably fried. There are 2 parts, mechanical and electrical. The mechanical part is a spring on the needle assy that keeps the needle centered with no current flow indicating Zero, with current applied the needle will swind one way or the other depending on polarity. If the needle staye pegged the spring has broken or it took such a hit it jammed. Open it up and fix it, many times the wire burns off the terminal inside.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
toss it....
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
Sounds like I've got nothing to lose by taking it apart.
Let's assume I find it is repairable. I intend to upgrade my alternator (CS130 or 144) and will also upgrade my wiring by increasing the size of the wire from the alternator to the battery. I will most likely do this by running a new wire (& fuse links) parallel with the existing one. Wouldn't this change the calibration of a working ammeter? If so, is there a way to "rewind" the ammeter to read correctly again?
Thanks a lot for the discussion. It has been very helpful.
DC
Let's assume I find it is repairable. I intend to upgrade my alternator (CS130 or 144) and will also upgrade my wiring by increasing the size of the wire from the alternator to the battery. I will most likely do this by running a new wire (& fuse links) parallel with the existing one. Wouldn't this change the calibration of a working ammeter? If so, is there a way to "rewind" the ammeter to read correctly again?
Thanks a lot for the discussion. It has been very helpful.
DC
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
Re-cal
If you'd tell me what gage wire you're going to, it's a sort of easy calculation to figure where the second orange fuse link is needed to get the same "voltage" as with the smaller wire. Since the ammeter isn't to accurate anyway, I can get you close. This all depends on if you can get the meter to function.
(I are an engnaneer, so it's part of my "nature")
Andy
(I are an engnaneer, so it's part of my "nature")
Andy
with your other post...