The Ford Barn

Krylon32 · 08-07-2023, 10:36 AM

I have a 40 coupe with the original gauges converted to 12 volts. The gauge just says battery. Is the gauge an amp meter or volt meter in a stock panel? I get mixed responses on the other forum. I have driven it 5000+ miles in the last year and everything was fine, gauge always in the green. About 2 weeks ago I was on a day trip and the gauge would only read in the yellow. It has a 150 amp Powermaster alternator. Wires are tight as is the belt. The battery is a 2 year old Red top Optima. I guess my next step is to obtain a volt gauge and see what's happening?

Terry,OH · 08-07-2023, 10:41 AM

For the Coupe and other passenger cars, the gauge is a voltmeter. Some of the larger models the gauge was an ammeter.

JayChicago · 08-07-2023, 11:10 AM

Quote:

Originally Posted by Krylon32

I guess my next step is to obtain a volt gauge and see what's happening?

Yep! I would first test at the battery to see that there is about 14 volts when alternator is operating. If good, test at the 12v-to-6v voltage reducer feeding the gauge.

With key-on/engine stopped, should see about 12v input and about 6v output. Gauge will be in the yellow.

With engine/alternator operating, should see about 14v input and about 7v output. Gauge will be in the green.

If input is good but output is not, voltage reducer has failed. (or maybe the connections there are loose? That would reduce voltage reaching the gauge.)

Krylon32 · 08-07-2023, 11:16 AM

I'm a dummy. Have built about 40 cars over the last 50+ years and this is the first one I've bought. I can't contact the original builder and in all honesty don't know a dam thing about the electric system except it worked good for 5000+ miles. I have no idea what the reducer looks like or where it's at. Never had any problem with the builds I did myself.

19Fordy · 08-07-2023, 12:11 PM

I think Jay has the right idea. First, check the voltage going to the gauge.

As a side note: Here's an interesting thread about 12V conversion and getting the gauges and the BATT gauge to still operate on 6V.
https://www.fordbarn.com/forum/showt...olt+conversion

JayChicago · 08-07-2023, 01:00 PM

Sponsored Links (Register now to hide all advertisements)

Actually, first check should be at the battery to see if the alternator is putting out about 14 volts. Chances are nothing suddenly went wrong with any of the gauge stuff. More likely the alternator has suddenly failed, which is not unusual. Your good Optima battery got you home. And the gauge is doing exactly what it is supposed to, in the yellow, telling that the car is working on battery only, charging system not working.

Bob C · 08-07-2023, 01:04 PM

According to the diagram on Van Pelt's site the way it's wire it's a voltmeter.

petehoovie · 08-07-2023, 01:29 PM

Quote:

Originally Posted by Bob C

According to the diagram on Van Pelt's site the way it's wire it's a voltmeter.

JayChicago · 08-07-2023, 02:13 PM

Yes, as per post #2. In 1940 it was a voltmeter.

51504bat · 08-07-2023, 03:00 PM

The gauge in my '39 p/u is a voltmeter not an amp meter. Don't know if its original to the truck but it matches the other gauges. Truck is converted to 12 volts and has a 1 wire alternator. No problems.

flatford8 · 08-07-2023, 05:54 PM

This question isn’t of any help to you but, are you sure the alternator is 150 amps?....to me that seems like a lot of amps that a classic car would never use.......Mark

Krylon32 · 08-07-2023, 06:43 PM

Mark; Car has air and 16 inch electric fan.

flatford8 · 08-07-2023, 07:04 PM

Ok....I gotcha now.....

aussie merc · 08-07-2023, 07:05 PM

multimeter at alt output stopped and running and again at battery should tell you whats going on

Krylon32 · 09-13-2023, 10:57 PM

Electrical system checked out good. Figured it must be the gauge. Found a NOS gauge at Southside. Only problem it was for a deluxe. My guy switched out the face, installed the gauge which worked perfect. Problem solved.

ssffnomad · 09-14-2023, 06:13 AM

Gary, nice outcome.

terry · 09-14-2023, 10:42 AM

For those of you who have switched to 12v and have no voltmeter, put a cellphone charger in your cigar lighter. Use one that gives you a constant digital reading of what the battery charge is. When at a car show, for looks, put the the lighter back in place. terry

tubman · 09-14-2023, 11:28 AM

Or... You can get one of these; they are quite cheap ($2.99 at WalMart) and work well. I used one to find an overcharge condition on my Corvette. I haven't tried it, but it would probably work in a 6 volt car as well.

Drbrown · 09-14-2023, 07:09 PM

Off-shore manufactured Alternators can be a problem. Sometimes folks prefer to get an old American made one from a salvage yard. If the bearings are okay its easy and cheaper to have the diodes replaced. I have a '47 converted to 12 volts - w/negative ground. On the way to the battery, the output wire from the alternator passes thru the metal loop on the back of the stock dash gauge and shows "amps" charging. I had a problem finding a "new" alternator that did not either shortly fail or one that would not exceed 14.5 volt output, which burned out my Pentronix distributor modules. So (1) I kept taking new one's for testing at a local electrical shop until I had one that worked correctly, and (2) I added a voltage gauge to keep an eye on the system. It is wired between my positive system (behind the dash) to the nearest good negative ground. One has to drive some distance before the voltage drops below 14 volts.

08-07-2023, 10:36 AM	#1
Krylon32 Senior Member Join Date: May 2010 Posts: 4,489	Battery Gauge I have a 40 coupe with the original gauges converted to 12 volts. The gauge just says battery. Is the gauge an amp meter or volt meter in a stock panel? I get mixed responses on the other forum. I have driven it 5000+ miles in the last year and everything was fine, gauge always in the green. About 2 weeks ago I was on a day trip and the gauge would only read in the yellow. It has a 150 amp Powermaster alternator. Wires are tight as is the belt. The battery is a 2 year old Red top Optima. I guess my next step is to obtain a volt gauge and see what's happening?

08-07-2023, 11:16 AM	#4
Krylon32 Senior Member Join Date: May 2010 Posts: 4,489	Re: Battery Gauge I'm a dummy. Have built about 40 cars over the last 50+ years and this is the first one I've bought. I can't contact the original builder and in all honesty don't know a dam thing about the electric system except it worked good for 5000+ miles. I have no idea what the reducer looks like or where it's at. Never had any problem with the builds I did myself.

08-07-2023, 12:11 PM	#5
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,950	Re: Battery Gauge I think Jay has the right idea. First, check the voltage going to the gauge. As a side note: Here's an interesting thread about 12V conversion and getting the gauges and the BATT gauge to still operate on 6V. https://www.fordbarn.com/forum/showt...olt+conversion Last edited by 19Fordy; 08-07-2023 at 12:16 PM.

08-07-2023, 01:00 PM	#6
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 732	Re: Battery Gauge Sponsored Links (Register now to hide all advertisements) Actually, first check should be at the battery to see if the alternator is putting out about 14 volts. Chances are nothing suddenly went wrong with any of the gauge stuff. More likely the alternator has suddenly failed, which is not unusual. Your good Optima battery got you home. And the gauge is doing exactly what it is supposed to, in the yellow, telling that the car is working on battery only, charging system not working.

08-07-2023, 02:13 PM	#9
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 732	Re: Battery Gauge Yes, as per post #2. In 1940 it was a voltmeter.

08-07-2023, 10:41 AM	#2
Terry,OH Senior Member Join Date: May 2010 Posts: 4,751	Re: Battery Gauge For the Coupe and other passenger cars, the gauge is a voltmeter. Some of the larger models the gauge was an ammeter.

08-07-2023, 03:00 PM	#10
51504bat Senior Member Join Date: Sep 2013 Location: SoCal-Redlands Posts: 3,024	Re: Battery Gauge The gauge in my '39 p/u is a voltmeter not an amp meter. Don't know if its original to the truck but it matches the other gauges. Truck is converted to 12 volts and has a 1 wire alternator. No problems. __________________ Making the simple complicated for over 30 years.

08-07-2023, 05:54 PM	#11
flatford8 Senior Member Join Date: Jan 2012 Location: Lyman,ME. Posts: 2,630	Re: Battery Gauge This question isn’t of any help to you but, are you sure the alternator is 150 amps?....to me that seems like a lot of amps that a classic car would never use.......Mark __________________ I'm thinkin' about crankin' My ragged ol' truck up and haulin' myself into town. Billy Joe Shaver

08-07-2023, 06:43 PM	#12
Krylon32 Senior Member Join Date: May 2010 Posts: 4,489	Re: Battery Gauge Mark; Car has air and 16 inch electric fan.

08-07-2023, 07:04 PM	#13
flatford8 Senior Member Join Date: Jan 2012 Location: Lyman,ME. Posts: 2,630	Re: Battery Gauge Ok....I gotcha now..... __________________ I'm thinkin' about crankin' My ragged ol' truck up and haulin' myself into town. Billy Joe Shaver

08-07-2023, 07:05 PM	#14
aussie merc Senior Member Join Date: Sep 2016 Location: sydney australia Posts: 1,034	Re: Battery Gauge multimeter at alt output stopped and running and again at battery should tell you whats going on

09-13-2023, 10:57 PM	#15
Krylon32 Senior Member Join Date: May 2010 Posts: 4,489	Re: Battery Gauge Electrical system checked out good. Figured it must be the gauge. Found a NOS gauge at Southside. Only problem it was for a deluxe. My guy switched out the face, installed the gauge which worked perfect. Problem solved.

09-14-2023, 06:13 AM	#16
ssffnomad Senior Member Join Date: Aug 2021 Location: Upstate N.Y. Posts: 443	Re: Battery Gauge Gary, nice outcome.

09-14-2023, 10:42 AM	#17
terry Senior Member Join Date: May 2010 Posts: 267	Re: Battery Gauge For those of you who have switched to 12v and have no voltmeter, put a cellphone charger in your cigar lighter. Use one that gives you a constant digital reading of what the battery charge is. When at a car show, for looks, put the the lighter back in place. terry

09-14-2023, 07:09 PM	#19
Drbrown Senior Member Join Date: Oct 2013 Location: Glens Falls NY Posts: 1,267	Re: Battery Gauge Off-shore manufactured Alternators can be a problem. Sometimes folks prefer to get an old American made one from a salvage yard. If the bearings are okay its easy and cheaper to have the diodes replaced. I have a '47 converted to 12 volts - w/negative ground. On the way to the battery, the output wire from the alternator passes thru the metal loop on the back of the stock dash gauge and shows "amps" charging. I had a problem finding a "new" alternator that did not either shortly fail or one that would not exceed 14.5 volt output, which burned out my Pentronix distributor modules. So (1) I kept taking new one's for testing at a local electrical shop until I had one that worked correctly, and (2) I added a voltage gauge to keep an eye on the system. It is wired between my positive system (behind the dash) to the nearest good negative ground. One has to drive some distance before the voltage drops below 14 volts.