short

[Jim B PEI]

This is such an interesting conundrum!  That narrows the problem:
1) it stops when you are *decellerating*
2) at *20 mph or less*.
3) *everything* goes out, lights, engine, all
4) starts back up in a few minutes; *full power*.

Here is my less-than-wizard take on this. I bet that there is some heat-related issue somewhere in this, if everything works in a few minutes. Something cools and contracts somewhere, and it might be electrical resistance heat, not engine heat. The slowing/stopping effort makes something move forward slightly/or the bearing down on the front end moves something slightly physically//maybe both at the same time--likely in a major cable, and the output of the generator is lost and everything dies...because at some point it was running only on the generator because the battery wasn't in the loop sometime after the car was driven for a while warmed up. Or, as long as there is sufficient flow through a wire from the generator, the (corroded?) circuit continues, but when the engine is running slowly at stopping/idle the load is too much and it "pops" out

The car sits, front end back up, leans back to normal stance, and once the wires cool, connection is made again.

One way to test if it is the battery would be to alligator clip a 6 volt test light, with a fuse of course, directly on the battery posts and have the light up through the gap in the hood. Then, if the light goes out when the engine/power goes out, you know it is the battery. If it stays on, then you know it is electrical wiring.

[Logan]

Okay, good battery test.  I'll see what happens with that.

[HJ-ETEX]

I have doubts that this the root of your troubles, but it may be helpful to others. 6V cars didn't have fuses except on added accessories like a radio or OD. Power from the battery went to a terminal on a 30 amp circuit breaker on the rear of the headlight switch. A short lead went from that terminal to the IGN switch so the ignition circuit was not protected by the breaker. The other, protected, terminal of the breaker supplied power to the light switch. If there was a bare spot in the insulation (rather common with the cloth insulated wire) that touched bare metal, the circuit breaker would click off and the lights and anything else connected to the light switch would turn off.
The important points are: 1) The breaker makes a noticeable sound when it cuts off although it may or may not make a sound when it cools off and reengages. It can click repeatedly off/on until the the light switch is shut off.
2) Most of the circuitry attached to the protected terminal of the breaker is lights so if you rarely used the lights (interior lights included) you may not encounter a problem.
3) The ignition is connected to the unprotected terminal of the circuit breaker (functionally as if the wire from the battery went directly to the IGN switch) so normally if there was a short that caused the breaker to engage, the lights would go out but the engine would still run. However, if the wiring had been altered to where the lead to the IGN switch was from the protected terminal, then the engine would shut off as well.

[pnw_oldmags]

We had a shorted out license Plate Light wire that had some funky symptoms,  Bat man bandage fixed it.

[Logan]

Took a long time for it to act up again, but it finally did yesterday.  When I put my light between the battery posts it came on = it's not the battery.  So, I tried what I did last time: removed the negative battery cable, roughed it and the terminal up, and put it back on.  Started right up.  I don't understand why, though, because there was no corrosion on the post or terminal.  But when this happened last time I did the same thing and it started.

[kaiserfrazerlibrary]

The 6-volt electrical systems are very sensitive to ground conditions.  What would pass as typical corrosion on a battery cable in a 12 volt system is serions on a 6.  You note the car tends to do this going down hill.  How secure is the battery in its holder.  Even slight shifts of the battery can change the contact between terminal and cable; if the cable is only fair, it could be enough to cause a problem.  I would suggest changing both cables with 1 gage insullated (to solenoid) and 1 gage ground strap.  These cables should be available (if from no other source) from a tractor parts place;  tell them it is for a 1950's vintage 6-volt Allis-Chalmers or Massey-Ferguson.  Insist on 1 gage; higher numbers are thinner cables and that also impacts current flow and grounding.

I speak from experiences with my first K-F car back in the mid 1970's (a 1951 Frazer Standard sedan).

[Fid]

I second that. Dirty or corroded battery cables often look just fine.  I had it happen to me once where I just drove my car to the store (and I didn't bother put my toolbox in the trunk) and when I got in it to leave, it would not even click, much less turn over, when I hit the starter.  I had to walk across the street and buy a wrench, take the ground cable off and despite the fact that it looked perfectly clean, scrape it up with my key, put it back on and tighten. Car started right up and I returned the wrench for a refund.  The 11th commandment is always "Thou Shalt Not Drive Thy Old Car Anywhere, Anytime Without Thy Toolbox."

[Logan]

Well, I guess that's what it is.  Just very sensitive to any corrosion.  By the way, I do have 1 gauge cables on there and they are from Antique Auto Battery, and I am not 100% satisfied with them as I said in a previous post, because they seem to be a little loose where the copper wires attach to the terminal that hooks onto the solenoid.  In fact, that in and of itself might be causing me some problems, I guess.  Perhaps I will try a tractor supply store.

[Fid]

I've comment on the "Antique Auto Battery" cables a couple of times. My experience has been that they are poorly made junk. I've had to repair every one I ever bought - the ends fall right off them.  If you want points when being judged, they will help you. If you want a realiable car, go to a tractor parts outlet.

[Logan]

New cables, and WOW what a difference!  I had my local starter/alternator shop make some, and after I put them on it cranked over a lot faster--I hadn't realized how bad the old ones were.  Anyway, I'm assuming that will clear up my problem, but we'll have to see.

[Jim B PEI]

Yeah, second and THIRD that comment. Even if they LOOK okay, they are junk. Go to any tractor dealership and have their parts department make up a real 00 cable or too. Diesel tractors need LOTS of cold cranking amps, and hot cranking amps, so tractor guys do it best. PERIOD!