Low voltage at ingnition circuit terminal block

clh333

New User
Hi, everybody! I'm a newbie with an ignition / electrical question.

I have a '48 8N (front distributor) which has been a good runner for years but now is balking at starting. It had run as recently as a month ago.

Attempting to diagnose the problem I first drained the gas tank and replaced with fresh gas. That did not solve the problem. Next I charged the battery, also without results. Then I removed / cleaned the terminals at the ignition switch. No success.

At this point I got out a meter and measured the voltage (to ground and to the + terminal of the battery) of the leads at the switch. I found about 1 Volt potential, which seemed too low to drive the coil. I checked the meter on a known DC voltage (12 V), checked the battery (6 V), then checked the terminal block that the leads were coming from, on the hypothesis that oxidation / corrosion was affecting current. I found 1 Volt there as well.

Here I am at the limits of my knowledge, so I got out the manual and found the wiring diagram. The motor turns over so I know the wiring from battery to solenoid is good. From solenoid the wiring goes to one side of the ammeter and from the ammeter to the terminal block. From terminal block to switch and back, and then to the coil.

When I used to start the engine I noticed that the ammeter used to indicate a (slightly) negative reading until ignition occurred. Lately the needle doesn't move. I suspect the problem is somehow related to the ammeter, so my questions are:

Will it hurt anything - like the regulator - to remove the ammeter from the circuit temporarily?
If the ammeter is not at fault, where else do I look?

Thanks for your replies.

-CH-
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Run a jumper wire from the non grounded side of the battery to the top of the coil (bypassing the ignition switch and the resistor) Attempt
to start.
If it runs, your problem is in the ignition switch or the wire running up to the coil. If if still doesn't start your problem is in the
distributor.
All of the above assumes a good battery.
 
Re Harold's comment: " All of the above assumes a good battery. "

You should see 12.65 volts on a fully charged battery, and a specific gravity of 1.265 on each cell.

At 12.06 volts and 1.115 specific gravity your battery is at 25% charge.


Check your battery.
75 Tips
 
Hotwire your tractor as a test.

If you are a N-News Magazine subscriber, your issue should have just recently arrived. I have an article in there about hotwiring your tea to as a diagnostic procedure.
 
Bad/incorrect wiring is most likely the root cause. First, is the system 6V/POS GRN or switched over to a 12V job? Verify battery voltage static. The battery must sustain a full charge under load. If it is older than 5 years it may not be sufficient. A hydrometer is required or take it to your trusty local starter/alternator shop to be tested on their equipment. While he does that, verify the entire wiring system is correct. Do the basic fuel flow test and if it passes, move on to the electrical. Disconnect any lights just to take them out of the equation. They were never OEM from the factory -always dealer options. You can reconnect later once true root cause is pinpointed. No need to disconnect the AMMETER. That is not the problem in my opinion. When wiring is correct, take your VOM, set to VDC, and place one probe on the LH post of the OEM Ballast Resistor as viewed from the front of tractor looking at the back of dash, and the other probe to GROUND. The LH post is where the coil wire connects to. VOM polarity does not matter. No Ballast Resistor? Problem #1 identified. Unless this is what you think is a 'terminal block'. Once probes are set, turn the key switch 'ON? but do not crank engine. You should see battery voltage with points open, half that with points closed. Got a good result, do the same test only at the coil terminal post. If either test fails, the problem is most likely in the distributor. When did you last do a tune-up? If tests pass, next step is to check for spark. Here are some diagrams for the OEM 8N 6V/POS GRN wiring. You also need to get the essential manuals. The I&T F-04 Manual, the original 8N Operator?s Manual, and the ?39-?53 MPC are very important tools to have.

FORD 8N TRACTOR ORIGINAL WIRING DIAGRAMS:
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FORD 8N TRACTOR ESSENTIAL OWNER/OPERATOR/PARTS/SERVICE MANUALS:
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Tim *PloughNman* Daley(MI)
 

Thanks to all who responded. To clarify a few things:

This is a 6 Volt, positive-ground system. The tractor is stored out-of-doors but the battery, new two years ago, is stored indoors in the off-season and charged weekly.

"Bessie" came to me from another owner - who had painted her with a broom, apparently. She had been "rode hard and put up wet", as the horsemen say. She is fitted with a front loader (one of the main attractions, since I do a lot of wood-cutting) but the bucket was torn and the front hydraulic mount broken. With the loader attached working under the hood is a challenge. There are no front lights to disconnect and the rear light has never been connected.

I last performed maintenance on the distributor last year: new points and condenser, timing and points gap set manually, per an article in N News.

Two years ago I rebuilt the carburetor, three years since I changed the plugs, wires and distributor cap and rotor.

The reference to "terminal block" comes from the diagram in the Ford Operator's Manual, Tractors 9N, 2N and 8N (Copyright 1952) which seems to be a compendium of several publications. Page 363 contains the diagram which references "TERMINAL BLOCK-8NNN-14448". Located on the inside of the dash below the ammeter and above the ignition switch, it is this to which I was referring. I understand that it also contains a ballast resistor, nominally 1/2 Ohm, I think.

The FOM is the only reference I have, other than articles clipped from N News. I subscribed for years but let my subscription lapse a year or two ago, alas. I regret that I don't know how to insert an image with the posting; I could illustrate some of what I am talking about.

I will try HCooke's Q&D battery-to-coil test first and then follow Tim's suggestions for a more thorough analysis. I'll let you know what I find.

Thanks again,

-CH-
 
I suspect you have an angle mount/side distributor, but you haven't said for sure. The FORD front mount distributor when correctly tuned up will last 5 or more years easily. Ditto with side mount units as well. You still haven't told us if it is a pre s/n 263843 with the front mount distributor or after April, 1950 with the angle mount unit. We surmised it is a 12V switch over job. The N-NEWS is a fine magazine and no doubt have the correct info on PM and such. Many of the articles on electrical systems in the N-NEWS issues were written by Bruce(VA) or Chris Britton, aka SOUNDGUY. However, if'N ya wanna be an N-Owner, it's best to get the essential 8N Manuals as I showed you below. There are different wiring systems for the front mount and the angle mount. The OEM BALLAST RESISTOR is NOT used with the angle-mount(side) distributor setup, only with the front mounted units, and regardless if 6V or 12V. The side mounted distributor uses the terminal block, p/n 8NN-14448 and NO Ballast Resistor. There is no resistor in the terminal block -it is merely a junction post/block for wires to all connect to. Stop guessing! -leave that for lottery tickets. Know exactly what you have and are dealing with so you don't muck up something and/or let the smoke out of a component.

Tim *PloughNman* Daley(MI)
 
Six volt system, front mount distributor. Can't read the serial numbers on the block.

Following are reference materials:


cvphoto1462.jpg


cvphoto1463.jpg


cvphoto1464.jpg


It has rained mercilessly for the last week, and the tractor is stored outdoors. I will return to pursuit of the problem when the weather breaks. No success yet.

-Ch-
 
I had to order a hydrometer of sufficient precision to measure the specific gravity in the battery; local NAPA did not have one in stock. Arrived yesterday's USPS delivery.

Removed the battery from the tractor and measured (at 55 degrees F ambient) SG 1275 in each of the three cells; 6.39 VDC across the + - terminals. I think the battery is OK.

-CH-
 

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