How to read an ammeter?

[audiolofft]

Hi all,
I have an '86 Catalina 27, Universal model 18 diesel with a 55-amp alternator. Besides the key switch, glow plug and start buttons, the control panel has a tachometer, temp gauge, fuel gauge, and an ammeter, the latter calibrated to minus and plus 60 amperes, with the centered needle position at a theoretical zero. The thing is, the needle hardly ever moves from its center position.
When I started up the diesel yesterday, the center needle went slightly into the negative range, then slightly positive (right of center) as the diesel revved up.
Is the ammeter working the way it's supposed to? Does it only give a major negative swing if the batteries are depleted, then move well into the positive range as the batteries are charging up from the alternator?
Frankly, I'd rather have a voltmeter in the panel than the ammeter, but I'm not even sure the ammeter is working as it should. (The manual for the diesel is of no help.)
Thanks in advance for any help.

 

[Capt jgw]

You need to check Main Sail's threads on the Universal wiring harness. They are great engines, but their wiring sucks. If you have the original harness with it's trailer plugs and heavier orange and red wires running to and from the ammeter, that all needs to go ASAP. The plugs and full alternator current running to the panel and back is a fire waiting to happen.

 

[Stu Jackson]

jgw is right.

Engine harness upgrade: A comprehensive overview by Gerry Douglas Important WARNING for M25 owners


Engine Harness Upgrade from Maine Sail http://www.pbase.com/mainecruising/universal_wiring_harness_upgrade and http://forums.catalina.sailboatowners.com/showthread.php?t=135558
Engine harness upgrade by Capt. Al
Important FIRE HAZARD for M25 series owners

Also read these with many engine related issues including the wiring harness:

Critical Upgrades http://c34.org/bbs/index.php/topic,5078.0.html

 

[Capt jgw]

Thanks for the links. Can't do that from my phone.

 

[audiolofft]

Thanks, Capt JGW, for the suggestions. I've read through a number of Maine Sail's threads on the Universal wiring harness and possible upgrades.

 

[audiolofft]

Thanks very much, Stu, for the links. Lots to read and absorb while I wait for a thunderstorm to pass.

 

[mz4wheeler]

When I started up the diesel yesterday, the center needle went slightly into the negative range, then slightly positive (right of center) as the diesel revved up.

This is exactly how it should behave, *IF* you have great batteries and have a good charging system. Think about it, from a battery perspective, starting a TINY diesel is nothing for new batteries.

My point it that the batteries barely discharge, so very little current is necessary to charge it back up to specs (hence, the low amp meter reading). Not talking about voltage here.

Having a high amp meter reading (constantly) is a sign of things going bad.

My 2 cents.

 

[Jdaniel343]

It should stay at 0 or just slightly +. This is a good thing. To much + is a bad thing. If the engine is running and it is in the - then the batteries are not charging and the alternator or regulator is bad.