The Stovebolt Site Forums The Shop Area The Electrical Bay Spiking Ammeter

Hi,

I've called Randy so many times recently with troubles over this that I thought I'd relieve him and ask the group for help.

About a month ago, I kept blowing fuses on my 37
1/2 ton, and at one point I fried my Runtz voltage reducer on the gas gauge. Randy diagnosed the problem as spiking ignition and advised that I wire a direct wire from the positive battery cable to the ignition switch. I did so, running a 10 gauge wire with fuse from the battery to the fuse panel, from the panel to the ignition. Everything works well now except the ammeter. When at idle it reads right at zero; but when I rev the engine or begin to drive, it spikes over toward 20. If at idle and I turn on my lights it goes far left into the negative, but if I rev the engine or begin to drive it, it again goes over toward 20. Randy suggested that there is a short somewhere in the system and advised me to track it down. I worked on it all day yesterday. What I did was begin removing each accessory, gauge, etc., one by one, seeing if I could eliminate the problem. Finally I had disconnected everything except the ammeter and the ignition switch--same thing. FYI, the ammeter is wired one side to the starter post, the other to the alternator (I have one of Randy's nice 12V internally regulated alternators). The ignition switch is fed directly from the battery through the fuse panel; the only other wire on the ignition switch is the one that goes to the coil--I had taken everything else off.

Since I was desperate at that point, I thought maybe something was wrong with the alternator, so I took it off and took it to NAPA for a bench test. It tested out good. Then I got another ignition switch and tried it--same thing. Then I dug out another 37 ammeter that I had and tried it--same thing. Then I found a newer ammeter from a JD tractor and tried it--same thing.

At this point I don't know what else to try--I've eliminated all the other connections, tried 3 different ammeters, and checked the alternator. I hesitate driving any distance for fear that I'll fry my battery. Help please!! Any suggestions?

Thanks,
Jim

Sounds like a short to me. Simply unhooking accessories might not be enough. Did you try unhooking wires that feed the power to the different accessories, such as at the junctions under the hood?

A test I usually try is the light circuits. I prefer to use a buzzer style tester, but an ohm meter will work. Disconnect the lamp wires at the switches and remove the bulbs, you need the circuits isolated. You can do this one at a time or all at once, depends on your comfort level for re-assembly. Then check between each bulb socket and ground, and follow the wire to the switch, wiggling everywhere it goes through any clamps and holes. This is where the buzzer comes in handy, you can hook it up and leave it alone while you're under the vehicle. Most shorts that I have found have been where the harness frot the tail lamps go through the retainer clips.

Fred,

Thanks for your advice. No, I haven't gone as far as you suggest--I guess that should be the next step. Can you tell me where to find such a buzzer tester. In addition, can you briefly explain how you hook it up, for example, on a light fixture in order to test for the short? Do you place it between the bulb and the wire hookup, then check/wiggle wires to listen for the short? Thanks in advance for your further advice.

Jim

Buzzer we have is a home-made affair. Don't have any plans, but I'm sure there are some simple plans on the internet. Maybe someone else here knows either where to get one or the plans put one together. To connect to the lamp wires, you can push the wires out of the socket after you take out the bulb. Then use an alligator clip to connect to the button on the end of the wire. Hook the other wire of the tester to a clean chassis ground.

:)howziit guys!

sorry for responding late, but i just got on-board, and decided to put my 2 cents in.

methinks that there is nothing wrong, per se, in these symptoms.

the ammeter reads ZERO, just sitting still. NORMAL.

ammeter reads heavy DISCHARGE, when headlights are on. NORMAL.

ammeter reads HIGH OVERCHARGING, when engine is revved. NORMAL.

i was just reading the instructions on my PAINLESS WIRING kit. they did not recommend wiring an ammeter into the system...if using a 65+amp alternator.(I wonder why?)

you are experiencing SHOCKING readings on your original ammeter, which only meters 20AMPS...charging or discharging.

your 20-0-20 ammeter is trying to measure output of a 65+amp alternator...hence the high reading.

the power draw of headlights is proportionally higher, on a 20-amp scale...hence the high-discharge reading.

if you were to install an aftermarket 60-0-60 ammeter, the DISCHARGE-OVERCHARGE readings would seem more NORMAL.

that's why PAINLESS WIRING does not recommend ammeters wired into the circuit.

FWIW, you might have some difficulty FINDING an aftermarket ammeter. though, for some reason, VOLTMETERS are readily available.

don't worry about frying your battery. if everything else is up to par, the REGULATOR ensures that this does not happen.

regarding your voltage reducer, the most important thing is if it's allowing the correct 6 volts to the gauge, or any original electrical item in question.

you can check this with a simple volt-ohm meter, testing one lead to the gas gauge, one to ground.

if 12 volts(or ZERO volts) are there, the resistor is kaput.if less than 6 volts, the resistor is too large. if greater than 6 volts, the resistor is too small.

the best resistors are the adjustable ones; with gas gauge and voltmeter lead on-line, you just turn the resistor's knob, until...VOILA! 6 VOLTS!

BTW,i don't think you have any electrical shorts. if there were no fuses to blow, the wiring would overheat, and cause an electrical fire.

you can buy the volt-ohm meter, the buzzer tester, the light probe, an audio oscillator(aka signal generator,beeper or toner)and matching probe, at your local electronics supply store.

me...the phone company let me keep all my tools...when i retired. :rolleyes: :rolleyes: :rolleyes:

i'm no professional; just my two cents' worth.

57--

You may not be a professional but seem to have these electronics down. Hope ur sticking around as I'm planning a rewire job this winter. If you got any picks of ur projects--post em --I'm sure we would enjoy em.

I would agree with 57 that the readings are normal. However, they do tend to stabilze a bit, especially the charge reading when giving gas, when the battery is fully charged or accepting & holding a charge (meaning a good battery). A weak battery will not hold a charge well. Thus the constant extreme charge & discharge. Also, possibily the regulator may require some attention.

howziit again guys!

thanks for the comp, Bznhafdzn! electrics...i'm familiar. electronics....GONGGGG!

my kids program the vcr, and i can barely navigate this computer! LOL!

Heyyyyy, i'm in the process of replacing a '77 camaro wiring harness in THE PINK LADY, with PAINLESS WIRING.

my wife is afraid to ride in it, after not starting three separate occasions. "honey, i said, don't worry. all i have to do is say a prayer, jiggle some wires under the dash, and it starts up!"(true story; go figure!)

as soon as i figure out the scanner and digital camera, i'll post pics.

i also agree with Donsz; if the regulator is operating properly, the charging display should be minimal...unless, like Donsz says, the battery or regulator is kaput.