Six volt wiring, generally........

[Go Fleiter]

Yesterday finally I found time to change my licence plate bulb. Before discarding it, I checked it up in my shop ? it was working. So I took my Voltmeter and found 6.1 V on the fixture poles. After cleaning up any suspicious corrosion, bulb didn?t light up again. Checking Voltage at the bulb resulted in 1.3 V with bulb vs. 6.1 without. That is a typical heavy ground resistance: nearly no problems without load and Voltage breakdown with load. The pressure of the closed lock plus its boltings to the lid did no more provide sufficient ground too. I ran a ground wire from trunk lid to chassis and problem is solved. Greetings! Go

[Don Coatney]

Just on a point of originallity, the ground strap went from the transmission to the frame in the area of the 'X'. It can usually be found connected under one of the transmission covers bolts. I've never seen one out in the open on the side of an engine. :)

Plymouths;
My posting was not to show originality but to show what works for me. I have seen several cars (all brands) with a ground strap installed as in the picture of my car. Actually I was surprised nobody made an originality comment about the oil filter in the picture of the engine installed in my P-15.
Don Coatney

[FourDoor]

Just on a point of originallity, the ground strap went from the transmission to the frame in the area of the 'X'. It can usually be found connected under one of the transmission covers bolts. I've never seen one out in the open on the side of an engine. :)

[Don Coatney]

Excellent advice Carla;
In the late 1950?s while working as an unpaid gas pump jockey at the neighborhood gas station I learned a lesson from a wise old mechanic. Most automotive electrical problems are the result of poor engine to chassis grounds. When troubleshooting any automotive electrical problems the first thing this guy would do is install a ground strap. This alone cured many of the problems. I installed the pictured ground strap on my P-15 before I initially fired the engine after the rebuild. This grounding problem is also common to 12-volt vehicles and your advice applies there as well. Thanks for posting.
Don Coatney

[Carla]

Hello, POC people,

I was just now reading the comment about a wiring problem, and thought I'd offer a few ideas, if I may.

There are some 'facts of life' about the generality of 1920's-'50's  6V systems which, when properly addressed, will have your 6V car/truck's electrical components performing as well as new. The 'catch' is that 'there's no free lunch', and it does take a bit of time and effort to attend to all the necessary little details.

The 6V systems are inherently quite adequate for reliable operation, but the newest of them are now a half-century old, and 'time takes its toll'. The primary problem with the generality of 6V systems is the subtle deterioration associated with sheer age. Testing of the major components, such as the starter, generator, distributor etc., really should be done with specialist equipment, but one can often get by with a bit of 'field expedient' improvisation.

As the wiring components age, they tend to develop corrosion....in theory, this can be forestalled with suitably plated parts and by painting completed assemblies with glyp or other insulating varnishes, but thats theory......out in the real world, those components, such as the various terminals and joints in the system, are slowly and steadily growing a coating of oxides, or so-called 'corrosion products'.

These oxides become a form of 'resistor', causing the 'evil' of 'voltage drop under load conditions'.....which is pretty much the same concept as putting a kink in a garden-hose.

When you have only six volts of 'pressure' to transmit the required amount of 'wattage' needed to operate the 'load', it doesn't take much resistance to create a problem level of 'voltage drop under load', i.e., a relatively little bit of 'resistance' anywhere in a 6V circuit will disable the component it feeds.

The 'cure' is actually quite simple, and really is just normal 'preventive maintenence', of the 'once a year' variety. (and this is a perfect example of 'do as I say, not as I do'....all of our vehicles are on the 'deferred maintenence scheme', I'm ashamed to say)

You simply take each wiring terminal loose, and brighten the surfaces with any suitable mild abrasive, such as steel-wool, a very fine stainless wire 'tooth- brush', 400 grit emery paper. This removes the 'resistor' oxides. At the very least, loosen the screw or nut, and wiggle the terminal back and forth, to break/scrape the oxide layer, then re-tighten.

As you know, one side of all the 6V circuits is 'ground', meaning that the chassis of the car/truck is, in effect, another wire. One of the more common problems with a 6V system is 'bad grounds', meaning that the affected component has a high-resistance connection to the chassis. The answer, of course, is obvious, cleaning the various grounding points to bright metal, and making secure connections.

There is a point there which quite a few 'mechanics' seem not to understand. The primary amperage draw is the starter, of course, so the battery positive cable (on the 6V Mopars)  really should go to the engine, as close to the starter as is feasible.

Consider the plight of the 'foolish virgin' mechanic who bolts the battery ground cable to the chassis frame. Consider the amount of wattage of 6V power the starter needs, and consider how that power will be transmitted from the chassis to the engine block, thence to the bell-housing and the starter case. The 'Floating Power' engine mounts aren't very good conductors of 6V power, are they? The answer, again, is obvious. An engine-to-chassis ground cable, of the same size as the main battery cables, will provide full voltage/wattage to the starter.

(Interestingly, a 6V engine will often seem to crank alright with the ground cable bolted to the frame, presumably cos all those little hard-working electrons find ways to bypass the rubber engine mounts......through the back springs, maybe, to the back axle, then up the drive-line to the gearbox, perchance? Maybe some of them run through the choke and throttle wires, and a few more through the wire re-enforcement in the fuel flex line?)

There are plenty of other places in a 6V system where age-related problems will cause diminished voltage under load. A common one is corrosion in a wire at a terminal. The terminal may look alright to a visual inspection, but  have corrosion at the point where the wire is clamped into the terminal. This is usually due to poor solder joints, or un-soldered replacement terminals. Sometimes, the wire will have been flexed enough to break some number of the strands. The cure is simply a new, high-quality replacement terminal, properly crimped and soldered (with 60 tin/40 lead best quality rosin-core solder) to the existing wire.

Sometimes, albeit rarely, a wire will have been damaged at some point in its run. Feel for a warm spot under load, as resistance creates heat, that is evidence of damage. Look for evidence of chafing, or other physical damage to the insulation.....a highly resistive short to ground may eventually get the wire hot enough to cause a fire.

A good test for suspected bad wires is to put a good voltmeter on the switch side of the wire, with the wire under its normal load. Read the voltage at the feed-point, then at the load component itself, and note the difference. If there is any noticeable voltage drop, run a 'test lead' of known good wire, of adequate size, and observe voltage under load again. Run a new length of wire if necessary.....wire is cheap.  Check the load component itself, and, of course, its ground. For example, its common that headlights will be grounded to the front fender, and enough rust will have formed between the fender and the chassis to act as a resistance. A good procedure is to run a new ground wire directly to the chassis frame.

Most of the component tests on 6V cars/trucks can be simple 'substitution' tests. A good example might be a sealed-beam headlight, which comes 'on' but is 'dim', yet the voltage at the wiring reads good. Its entirely possible that the only bad part is the sealed-beam itself, so substitute a known good one and see what happens. Another cause of dim lights could be a bit of resistance in the light switch itself....try jumping around the switch, and see how the lights look then.....or iif the switch gets warm under load, for example, have it apart and check out the contact points.

This, rather obviously, applies to ignition systems also. When I was working in the truck shop, back in the late '60's, we commonly carried a 'test coil', as a quick check on hard-starting engines. This was just a known good coil (I carried a 'Mallory hot coil') with a bracket taped on so it could be hung from the bonnet rods, with lengths of clip-leads to jump to dist primary and to battery cable at the starter. This, as you see, by-passed the entire wiring-switch-coil of the ignition system with a known good system. I also carried a Mallory condenser on clip-leads, to by-pass a suspected bad condenser in the dist, if needed.

Automotive electrical work, particularly on the old 6V systems, is actually a little sub-trade all its own. Experience in the radio/electronic field has little relevance, surprisingly enough.

For those of you who are on 'learning curve' about the 6V systems, I'd like to strongly recommend an old (1946)  book, which explains 6V automotive work clearly and simply. The title is 'How to find a short', by 'Jack Steele'. (if I can ever find my copy, I'll see whether the copyright is still active, and, if not, I'll see about having a short run of copies made)

I did a moment's looking on the internet, and found several book-sellers offering copies at rather ludicrious prices, so I'd think a bit of 'haggle' is in order.

So endeth the sermon for today........ : )

More later, if anyone's interested.....

cheers

Carla