The Snakes Alive CMP Wiring Project

[Jordan Baker]

Very nice work.

[Jacques Reed]

Good Day,

Thought this may be of interest. Found these yesterday in a junk shop in Melbourne. NOS 6V Ford script headlight globes.

Interestingly they say "Made in Holland" on the base.

I guess it is safe to assume that they were made post war! Part No. indicates a 1941 design. Must have made them for only a short time afterwards as sealed beams were in common usage by then.

You just never know what will turn up 70 years later.

Just noticed in Parts list * C01Q 13009 Bulb 32-21 C.P. 6-8 Volts is lower candle power on High than these at 50 C.P. on High. Better illumination with these ones but draws more current.

Cheers,

[m606paz]

Can help me with this Ford wire no listed in part list?

[Andrew Rowe]

Part number would almost suggest that this is for a Rear - engine armored car,
For the Indian Pattern one's, armored cable, Cheers Andrew.

[Jacques Reed]

Some aspects of the following may have been covered before on MLU but it may still be of interest to restorers.

I have noticed most wiring diagrams in Ford CMP Maintenance Manuals and Handbooks do not show the wiring for an ammeter equipped instrument panel. A discussion about wiring with a fellow MLU Member prompted me to investigate it a bit further. The only reference I could find was a 1945 Australian “Drivers Handbook for Ford” which showed an “Ammeter” in the dashboard layout diagram. All other publications show it as a “Battery Indicator” There are also some wartime Ford commercial truck wiring diagrams showing an ammeter and not a battery indicator.

Thanks to Mariano Paz’s 1945 Ford CMP wiring diagram data plate, my original harness, and the link below I have a clearer picture. Also going back to Electricity 101- Ammeters vs Voltmeters helps to make it clearer. Ammeters- measure current flow in a circuit and placed in series. Voltmeters- measure electrical potential difference between two points in a circuit and placed in parallel.

1939-40 Fords, Mercs, and Lincolns, and early war CMP’s used a gauge with “BATT” displayed on the face which is really a voltmeter. Ammeters display “DIS-CHG” on the face. Later in the war, the Ford commercial instruments, used in the CMP’s, were changed from battery indicators to ammeters. This was prior to the military round gauge instrument panel being adopted. As of the May 1943 F15-A Spare Parts List. however, only “Battery Indicators” are listed, and not ammeters.

On indicators with “BATT” displayed the current flows from the starter solenoid first to the voltage regulator battery terminal, then to the ignition switch, and then to one terminal on the Battery Indicator. The other terminal on the indicator goes to earth. This is shown on all the early wiring diagrams and is correct. I must admit I thought in the past that was wrong but I was looking at my ammeter’s wiring and not that of a voltmeter.

When the Ford commercial ammeters replaced the battery indicators on CMP’s the wiring could be the same for both the Ford gauges and the military round gauges. The current flows from the starter solenoid to the ammeter first, and then to the voltage regulator battery terminal. If an early BATT gauge harness is used on an ammeter equipped truck or an ammeter harness used with a battery indicator equipped truck it could cause serious electrical problems.

Things to keep in mind if repairing, making or buying a wiring harness, or changing gauges.

And yes, the battery indicator and oil pressure gauges are on the wrong side in the photo and “BATT” should be on the bottom. That’s how I bought it.
I have been told the gauges are the same and can be used if you change the faces, but you can only swap a BATT, not an ammeter, with the fuel gauge, and the temp with the oil pressure gauges due to the mounting hole positions.

Hope this is of some help and interest.

The following link may help to explain it all.

https://fifthaveinternetgarage.blogs...gauge-and.html

[Ganmain Tony]

Following Jacques excellent information, found this diagram in the drivers book.

Ford Special Pattern Vehicles Third edition, Page 184.

[Jacques Reed]

Good Day,

A while back I noticed a short 22" long wire attached to the left side of the small harness on the Ford cab 13 shell. It lead nowhere and had been cut, but tracing it back it went to the sidelights terminal on the terminal block. On that basis it was most likely the original lead to the left sidelight. It reached all the way to the left sidelight and when moved to the tail at the terminal block for the right sidelight, it would also reach the right sidelight.

Looking at the parts list, the sidelight assembly is a different part number to the tall and stop light assemblies. It could be the different lenses fitted and it could also be the different lengths on the leads. The tail and stop light leads are much shorter.

If a short tail/stop light fitting is used as a sidelight it would require a short wire with bullets both end to connect to the shell harness. I doubt if Ford would waste the extra resources to accomplish this so I am 99% certain that the sidelights had longer tails. I made mine 24" long just to be on the safe side and they connect up perfectly.

Just some more good intel from my $400 parts truck.

Hope this is of some interest.

[Tony Smith]

Originally Posted by Jacques Reed

Ammeters- measure current flow in a circuit and placed in series. Voltmeters- measure electrical potential difference between two points in a circuit and placed in parallel.

Later in the war, the Ford commercial instruments, used in the CMP’s, were changed from battery indicators to Ammeters. This was prior to the military round gauge instrument panel being adopted. As of the May 1943 F15-A Spare Parts List. however, only “Battery Indicators” are listed, and not ammeters.

When the Ford commercial ammeters replaced the battery indicators on CMP’s the wiring could be the same for both the Ford gauges and the military round gauges. The current flows from the starter solenoid to the ammeter first, and then to the voltage regulator battery terminal.

Hope this is of some help and interest.

Don't know why I didn't pick up on this at the time.

The Ford Commercial Amp Gauge IS NOT wired in series. The gauge uses an inductive coil to measure the current flow (and direction). Look at the back of the gauge. There are no terminals, but there is a steel "bridge" device. The wire from the "Batt" terminal on the voltage regulator (itself in turn connected to the neg terminal on the battery) to the Starter solenoid is an 8ga wire and PASSES THROUGH this bridge. The current flowing through the wire creates an electromagnetic field, the strength of which is read in the inductive coil, and deflects the needle on the gauge.

The later round "Military" Amp gauge does have terminals on the back of the gauge and IS wired in series, and the wire from the Voltage regulator is in two lengths with terminal ends that connect to each terminal on the back of the gauge.

So the wiring harnesses for "Ammeter+Commercial instruments" and "Ammeter+Military Instruments" are different. If you have the early "Inductive" style harness, it is a simple matter of cutting the VR to Starter wire and adding terminal ends to suit the Mil gauge. If you have the later "Series" harness, you need to replace the VR to Starter wire with a single length of 8ga wire.

The Inductive Amp gauge was probably superceded for reasons other than just the availability of round military gauges. The Inductive coil gives a good "Indication" of charge/discharge, but is not terribly accurate for the actual current amperage value compared to a gauge being wired in series. In addition, the unsecured wire passing through the bridge is prone to chafing and shorting out, particularly on a military vehicle which might be expected to see some rough roads and a lot of shaking. Worst case is a vehicle fire, best case scenario is a shorting out of the electrical system and a "Fail to Proceed".

[Jacques Reed]

Tony,

It appears there are two types of Ford ammeters used on the Ford CMPs then.
I took my information from the original harness after tracing out the wires. That round gauge ammeter has two terminals and is wired in series to the voltage regulator from the battery.

Second photo is the back of a NOS Ford Ammeter also with two terminals. The lower left gauge. The face of it is shown in a previous post and has the same face as the one you show.

Added a 1941-42 Truck wiring diagram showing the ammeter in series.

IMG_0076.JPG IMG_3670.JPG

wiring diagram 41-42 truck V8 only.jpg