The Stovebolt Site Forums The Shop Area The Electrical Bay Ammeter Negative Post Output

I need to replace the output wire from the ‘negative’ post of the ammeter to the key switch. On the wiring diagram there should be 4 things (key switch, heater fan, turn signal, flashers) feeding off that ammeter post, but my ammeter only has one 10 gauge wire on that post (the left one, see attached pic). Do these other circuits split off from a terminal block somewhere? In particular, the wiring diagram makes it look like the 10 gauge wire from the voltage regulator to the negative terminal has another 10 gauge wire to the ignition switch that splits off before getting to the negative terminal of the ammeter.

Anyway, the goal here is to replace the wire that powers the ignition switch.

What year is your truck? My '51 has a splice on that 10 ga wire coming from the ammeter. Also the 1948-1949, 1950-1951, and 1954 wiring diagrams I have show a splice to at least two additional wires a short distance from the ammeter terminal. I had to renew the splice when I rebuilt my wiring harness.

My ‘52 had a four wire splice about a foot from the ammeter that was soldered and taped. I replaced it with crimp on ring terminals bolted together then added heat shrink tubing to insulate it.

1949 3600 with 235 and SM420. Converted to 12V and retained the stomp starter.

OK thanks guys. Didn’t imagine that the factory harness would come with splices (or even stranger, splices with different gauges!). So I’ll go searching for splices downstream of the negative terminal.

Just to clarify (‘cause wiring is not my expertise): the two wires on the right (positive) terminal are for power out to charge the battery (10ga) and power out to the fuse block (16ga). On the left (negative) terminal is a single 10ga wire that splices to 10ga coming from the voltage regulator B terminal, and also splices to a 10ga wire powering the ignition switch.

Somewhere on that 10ga wire from the left (negative) terminal there should also be splices for the heater (12ga), brake lights (16ga) and turn signals (16ga). The wiring diagram makes it look like those last three come directly off the left (negative) terminal, but that’s obviously incorrect as I only have the one 10ga wire connected there (and the turn signals, fan and brake lights all work)

Most aftermarket ammeters have one long threaded stud that will accommodate multiple ring terminals. I think that maybe some OEM meters are the same. That junction serves as a distribution block for several circuits- - - -ignition switch, generator/alternator output, headlights, heater blower motor, etc. There should be only one conductor on the other terminal- - - -the wire from the ammeter to the battery cable lug at the starter. Wired that way, the ammeter can serve its function properly as a charge/discharge indicator. Another option would be to run a single wire from the ammeter output terminal to a junction block or fuse panel, and do the circuit distribution from there. Stovebolts are notorious for a severe lack of fused circuits, resulting in a "positive smoke check" of the wiring harness in case of a bad short. It's a very good idea to include a fusible link in the wiring from the starter to the ammeter which will burn out before wiring harness damage happens in case of a severe short situation. Splices anywhere in a harness are few and far between on factory wiring. It's more likely to be a cobble job by "Bubba Bad Pliers" sometime in the past 60+ years.
Jerry

I agree with Jerry. If there are wires to connect and if the stud on the ammeter is long enough to accommodate them, I'd attach the wires there instead of splicing them to another wire.

My truck still has its original wiring under the dash and there are no splices that I saw while under there wiring up the instrument panel lights.

Papa, to clarify: I see you know this already because you use parenthesis or quotation on the words negative and positive, But for the archives and other folks:
The symbols on the face of an older ammeter (-) and (+) signify discharge and charge. They don't signify the normal use, I.E. voltage and ground. The ammeters don't have those markings on the back. both terminals on an ammeter are positive voltage potential. Both are positive. But to discuss how to wire, folks always ask which terminal gets direct battery voltage and most of the time it's the terminal behind the (+) mark and/or "C" on the face of the meter. The loads are on the terminal behind the (-) and or "D".
As the years went by the (+) and (-) went away on ammeters. Just D and C or dots.

The factory diagram for 1949 trucks (foot start type) is what I'm using, hope you are using that. I may repeat some of what you said.
So according to the diagram:
1. There are two wires on the ammeter "positive" terminal. One "comes from" the big lug on the switch mounted on the starter. This wire is not to charge the battery. The other wire "goes to" the fuse block but is not powering any fuses. It is using the fuse block as a junction for the horn.

2. The "negative" terminal has all the loads, headlight switch, VR (battery charging circuit) and ignition switch. A heater or signal (not shown on the diagram) would get their power from the ignition switch, probably thru a fuse. These load wires, as noticed, get there however they get there. By jumping off a junction device or direct to the ammeter terminal.

You may find changes/additions made by other owners do not match the factory 1949 Chevy truck diagram.

Here's an excerpt from the 1948-1949 wiring diagram with some colors added to help trace the wires.

The Red wire is from the Starter Switch terminal to the ammeter.
The Green wire comes from the ammeter and goes thru the fuse terminal block to the horn to power it.
The Blue wire comes off the ammeter terminal and goes to a splice, then to the voltage regulator, the light switch (power input), and to the input of the ignition terminal.

The wires marked with a triangle are only for trucks with a pushbutton start and solenoid.

Hope that helps clear things up.

One thing for all to remember who have an ammeter. If you add some component, don't wire it to the battery or to any hot spot before the "positive" terminal of the ammeter.
This includes not wiring to the starter stud. When that component is on, the ammeter will indicate a constant charge. OK for a horn. That is momentary.
Wire the new component to the load side of the ammeter, wherever that may be.

Thanks guys, that’s all very helpful. My wiring is just like KLH’s posted wiring diagram: there’s two wires off one post of the ammeter and one off the other, but downstream of those are factory installed splices to power lights, fans, turn signals, etc.

Otto, the factory splices are buried in the wiring harness and so are very hard to find.

I finally got my new temp gauge and so will be putting the whole cluster back together tomorrow and replacing the burnt out wire to the key switch. My ammeter posts are long enough to accept lots of other wires, but I like Jerry’s strategy of adding an extra fuse block to power the factory spliced in accessories and then deleting the splices altogether. Will see how many of those circuits I can suss out and bring into the modern age of electrical wiring. A wire without a fuse is a strange notion even to my novice electrical skills.

So the wire feeding power to the key switch was completely fried and indicated multiple repairs over the decade. It started to cook at the factory splice that joins a #10 wire from the VR, a #10 wire to the back of the ammeter, a #12 wire to the lights and a #14 wire to the key switch! All with nary a fuse. I’ve included pics of these splices for general edification. They’re buried under the cotton mesh that forms the harnesses and so aren’t easily located.

The actual splices are crimped with a lug and soldered, so good solid work, it’s just the mixed gauges and no fuses that are a miss.

For now, I’m going to delete the burnt wire and replace it with new #12 and inline fuse running off the ammeter post. Then get busy shopping for a proper wiring harness kit with a full fuse set.

I had a similar issue with my main splice. That old cloth covered wire gets pretty brittle. I was able to renew it and it's held together so far. Part of the complete rebuild on my wiring harness.

So got the new temp gauge in the cluster and the whole shebang back in the panel. Running new wires and cutting out the old bad stuff worked just fine. Now I'm waiting on my Speedometer to come back from Deluxe in Colorado (yep, it was one of those, "As long as I got this apart I might as well . . ." I believe the military calls it, "Mission creep.")

No spark though. So I'm chasing that down. Doesn't look related to this rewire: I get good battery voltage at the coil (12.5V with key on), and 3 volts out of the coil (negative post to distributor), this is an internal resister type coil. The coil when isolated tests at 3 ohms between terminals, and 9K ohms between the positive and the high tension lead out. The distributor has the same 3 volts out of the coil to the block connecting the points, and 3 volts into the points. With the key off there's no continuity to ground for this circuit (from the coil to the points) so it's ok. I have one of Jon G's condensers, but also tried the distributor with an old style condenser. Both bench tested fine and neither made a difference.

But no fire, no spark to the plugs.

With the key on the coil - and the wire connection at the points should both read battery voltage if the points are open and zero volts if the points are closed. Sounds like defective points to me.

Good point Bill. I took those readings after cranking the engine a bit. This is an internal resistor coil, so it should start with battery voltage on both terminals, and then as it warms up the negative terminal going to the distributor should see voltage drop to 3 volts. I'll retest it at cold this morning and see if this coil is stuck at 3V all the time, or if it's delivering 12V for starting when cold.

3 volts on the coil - terminal is wrong no matter hot, cold, running or cranking as long as the coil + terminal has 12 volts on it.

It's one of those internally resisted coils, so it's supposed to lower voltage once it warms up.

When the points are closed they short coil - to ground. If coil - reads 3 volts, the points are not doing their job.

Bill, it looks like you're flagellating a room temperature equine here!
LOL!
Jerry

Papa,,,you have ignored what Bill said about points, or at least you don't mention it. It's the points, either need cleaned and adjusted or replaced. Do that instead of measuring volts and amps and trying to analyze the numbers. Logic says you have 12V at coil, Jon G condenser and coils usually last a long time and points (or condenser) are usually the cause of no spark.

Also important is to actually be checking spark across a plug's Gap.

This post had no question or issue until there was a no spark condition. Up until then it was a discussion about how chevy wired the truck to accomplish what the diagram says.

You test a coil by looking at the points to see if they are closed or open and get readings each way. But I suggest to stop checking coil. Concentrate only on the points.
You do need to be sure you have 12V to coil postitve when cranking.


I assume "no fire" means no sound or backfire/nothing when engine cranked. I assume "no spark to plugs" means you took a plug out and with plug wire connected, you laid the plug threads on a good ground spot, key on, cranked motor and watched to see a spark across gap, under dark lighting.

assume "no fire" means no sound or backfire/nothing when engine cranked. I assume "no spark to plugs" means you took a plug out and with plug wire connected, you laid the plug threads on a good ground spot, key on, cranked motor and watched to see a spark across gap, under dark lighting.

Correct on all assumptions. Visual inspection of the, nearly new, points looked good BUT . . . the points are nearly new because the last set had a contact point come off. So probably worth taking apart again. There was no visible pitting or burning.

Adjust points gap carefully to spec. Sometimes they move when tightening the screw. Make sure the rotor is in there.

I can't count how many times I found the rotor in my pants pocket after doing tune-up that wouldn't start afterwards..

😂 rotor in the pocket … I’ve done that one too!

Well as usual y’all were right. It was the points. Visually they looked perfectly flat and the gap measured fine, but they must have been sitting open all those weeks I was tearing into the ammeter and gauges and wiring harness and during the rainy season too. Must have oxidized them. I ran a points file through them and that 3 volts when closed dropped to nothing. Put the distributor cap back on and it kicked right off. 👍

Thanks guys!

Excellent.

Using a file on a set of points will be good enough to get a farmers tractor from the field to the barn, but it is awful hard on the points. The points work best if they are close to a mirror finish. Slightly oxidized points can be burnished with a business card until shiny. If they require anything more than that, you should get new points.