www.Amphicars.com

Converting your Amphicar to Negative Earth (Ground)

Why ? There are many benefits in converting Amphicar to negative earth, the main two for me are you can fit an alternator and you don’t blow up cellular phone chargers !  Mostly the conversion is straightforward and is documented elsewhere, the fuel gauge (details below) is the only part where you need to get a soldering iron out.  

The original Amphicar charging circuit, especially the voltage regulator, is not very good, the car will gradually loose charge at low RPM (in the water) if the lights and wipers are on, this is because the regulator changes output dependent on heat, if you set it to provide enough charge (voltage) when in the water at low RPM with a cool engine area - it will overcharge at fast road speeds and cook the battery. This is a know issue on other cars that use the same charging system (Triumph Heralds and early Spitfires) 

How ? It is possible to replace the regulator and repolarise the dynamo to change to negative earth but it's best to just junk the lot and fit an alternator - this is the main benefit of changing polarity. An alternator from a later Triumph fits without any major problems (although you need to remember to get the adapter block that fits on the engine block as the mountings are different) It then just connects straight to the battery - no regulator needed. You must at this stage replace the battery leads so they can not be connected the wrong way round as alternators are polarity sensitive. 

One other often overlooked thing to change in the engine bay is the ignition coil, these will continue to work after polarity is reversed but sometimes they fails after a few months, they are cheap and easy to replace so best not risk it ! Some people also replace the capacitor/condenser and points, not strictly necessary but as they are ordinary service items it's a good idea. The biggest technical problem is the fuel gauge. The horn should work as well as ever but best bet is to junk it anyway and fit one under the bonnet (sorry - hood) it is plenty loud enough there and protected from water. 

The only other thing you may spot is the wipers don't park as well as before, they still work fine but are a little bit up the screen, this is due to the way the cam actuates for self parking. If you take the wiper motor apart you can switch polarity to the motor which fixes the problem, reasonably straight forward but you might want to get the autoelectrician to sort this while he is doing the fuel gauge. 

Everything else works fine but watch for bilge pumps etc - and one other important point, I've ignored the bilge blower as we don't have those in Europe. The radios we tend to all use in Europe are Blaupunkt, particulalry the Frankfurt models W, X, Y and Z These fit in the original slot and even have lovely ivory knobs. They are 4 waveband. I have bough a couple secondhand from Germany so may have a spare one for sale. 

What needs to be done to the fuel gauge ? Inside the fuel gauge there are two coils that control the position of the needle, the direction of the current going through these needs to be reversed, once this is done and a minor adjustment made, the fuel gauge is accurate and NO external wiring needs changing and there is NO need for any special insulating washers or nylon screws etc.

How the fuel gauge works ? As mentioned two coils are used to control the direction of the pointer, the fuel sender is a simple variable resistor, with a completely empty tank there is 0 Ohms resistance, with half a tank of fuel there is 100 Ohms of resistance and with a full tank there is 200 Ohms of resistance. Because the Amphicar fuel tank is almost square the resistance is linear to fuel level, ie 25% full = 50 Ohms

If the cable from the gauge to the tank is broken or there is a bad earth on the tank then the gauge records a full tank. (Simply because there is more than 200 Ohms of resistance.)

This first picture is a photo of a schematic of the gauge from the front. (Oops, excuse the spelling !) Throughout this conversion I will reference everything as it will be when finished, that is Negative earth, the colour of the cables and there positions are original Amphicar, and do not need to be changed.

Ok, to work, disconnect the battery, ideally you should do this work as part of changing the car to negative earth but it shouldn’t do the fuel gauge any harm if it’s connected the wrong way, it just doesn’t work ! The back of the cluster gauge housing will look like this: (Note all Amphicar cluster gauges are date stamped Jan 1962, so, Happy 40^th Birthday !!)

Disconnect the 3 cables from the back of the gauge and undo the 3 screws that hold it in and remove the gauge from the cluster housing, now on the bench remove the 2 small black screws that hold the face on to the fuel gauge mechanism. For some reason these have glue on their threads and are difficult to remove but come out they must, you should then have a gauge that looks like this:

The pencil is pointing to the tip of one of the two screws that need to be removed next from the back of the gauge. This releases the pointer mechanism.

Now, soldering iron out, whilst it’s warming up look carefully at the very fine wires that come out of the two coils.

The top coil has one wire connected to the case shown by the pencil tip and the other wire connected to the top pin.

The bottom coil has one wire connected to the bottom pin and one wire connected to the top pin.

The top pin has the thick brown (or sometimes green) wire connected to it.

The bottom pin has the thick red wire connected to it.

OK, here we go, first unsolder both the brown and red wires.

Step 1. Very carefully, unsolder both fine coil wires from the top pin, make sure they are separate,

Step 2. Unsolder the wire from the bottom pin and whilst it is still warm solder it to the top pin.

Step 3. Take the wire that was unsoldered from the bottom coil in step 1 and solder it to the bottom pin, whilst still hot also solder the large red wire back on to the bottom pin.

Step 4. Unsolder the second wire from the top coil where it attaches to the frame and resolder it to the top pin, now resolder the grey wire to the top pin. Step 5. Now solder the one remaining loose wire, from the top coil, to the frame.

OK, all done, soldering iron off !  Check carefully the route of the wires and confirm there are no short circuits, make sure all is neat and tidy and refit the needle mechanism.

Now refit the dial face.

It’s a good idea to check for short circuits with a meter, if there are any shorts it’s possible things could get hot and at best you’ll burn out the gauge...

Ok, if all happy then before fitting you need to calibrate, you don’t want to be running out of fuel in the middle of the lake because the gauge doesn’t go right down to empty !

With no power the gauge should show be showing less than empty, what I mean is the pointer should be below 0, if it isn’t then bend the needle stop a little bit.

Connect 12 volts positive (+ve) to the terminal labelled  –  on the back of the gauge (see photo, yours may be rusty) connect 12 volts negative (–ve) to the centre pin that’s labelled with the earth (ground) symbol, the gauge should now show full.

OK now with everything still connected connect a second cable from the 12 volts –ve supply to the G terminal, the needle on the gauge should now show exactly 0  If not then look back at the third photo above, to the right of the pencil is a small tab with a little slot in it, with power still connected move this slightly to the left or right until the pointer is on 0 (don’t use anything metal for this adjustment !). Remove the cable from the G terminal and the pointer should drop slightly to the stop.

Finally put a small sticker or label on the back of the gauge saying negative earth.

And that’s it !  Now fit it all back, all cables go to their original positions.

If you get stuck or don’t feel confident I’ll do this for club members on an exchange basis for, say, $25 plus shipping, email me for details.