Ampmeter (not voltmeter)

[Lou Lyman]

Hope someone is knowlegable about this gauge question.

The 1966 mustang came with a shunted ampmeter. The shunt stops the pointer from fluctuating very much between charge and discharge. (I suppose this was to keep from alarming uninformed drivers) I have tried several ampmeters and can not detect any movement of the pointer. The charging system is working and has been for years, no problem. I just want to have a working gauge.

My question: Does anyone know of a repair facility that can remove the shunt or reduce the shunt action so the gauge will function and the pointer give a reading? Or do you have a simple "fix" that I can do? WOULD LIKE TO KEEP THE STOCK AMPMETER & NOT GO TO AFTERMARKET.

Thanks for any help or suggestion.

Lou

[Lou Lyman]

Since my first post I have learned that all ampmeters are shunted. So possibly the Ford has a higher resistance than other makes. Which brings me back to the origional question: Does anyone know of a repair facility that can reduce the shunt action so the pointer will give a reading?

Lou

[red]

if this dosn't help, post your question on the vintage board. A few electrical specialists hang out there too.

[Lou Lyman]

Thanks Red,

I took a quick look at your link and it looks like they will know the answer to my question. I'll get registered and post over there ASAP. Appreciate your help.

Lou

[Jeff65]

Ammeters require shunts. If they didn't have them, they'd soon self destruct. The factory sets up the ratio of current flow in the shunt, the main harness and the guage. Chances are you're seeing little movement because when all is normal, it doesn't move much. Here's the deal.

When you start the car, the ammeter will move negative as a lot of current flows into the starter. The battery is being drained at this time. As soon as the engine starts and the key is released from START, the current goes way down so the guage goes back towards center. As the rpm of the engine increases the guage goes right a small amount indicating it is trickle charging the battery. The amount of deflection isn't very much when you have a good battery. When you have a bad battery the deflection will be greater. This is so, because the good battery holds up to the start fairly well and the bad battery doesn't.

All you should care is:

a. ammeter needle is to the charge side when the engine is running above idle. The amount of charge indication is proportional to the deep discharge event that last happened.

b. If you see a continuing negative indication, it means you have a short or a large draw on the system the alternator can't satisfy.

c. The exact center of needle movement is not important, the direction of deflection when the engine is running is.

You can see the same indications on a voltmeter, its just the starting point is 12 volts instead of center of the scale. Voltmeters don't move much either, but its the tendency to move upscale or downscale that you have to learn to read.

[Rev]

I think that's how the stock guage measures it? My son's after market guage measured it with the whole amperage into and though the guage and out again through the interior. Not a GOOD ******* IDEA.

Indicated amps are better. I think that's why we use volts as an indicator today.

Rev

[Rev]

Thanks Dan for correcting my iill-advised use of the english language. I'll try to keep in mind your superior knowledge in the future, LOL.

Rev

[Lou Lyman]

I received lots of info here and a link to another board where some electrical gurus hang out. This is what solved my problem:

Any resistance in the wireing harness renders the ammeter inoperative. The firewall connector plug had corroded pins which when cleaned up solved my problem. The connector is to the left of the master cylinder and above the valve cover. Now I can see movement of the pointer so the gauge itself is not at fault. Ford acknowledged in a service bulletin that needle movement was only slight in 1966 models and any movement at all met their specs.

Hope this may help others who have the same question.

Lou

P.S. I learned how to spell "ammeter".