Why am I going through batteries? Alternator charging, current drain and CORRECT radio connections!.

I've had this car for about 3 years... in that time I have rebuilt much of her and driven the princely total of around 400 miles... I have also used 3 batteries!

The first was a high capacity battery I thought would last throughout the rebuild... but as it sat for nearly 2 years untouched I wasn't all that surprised when I found it was dud. I fitted a second (Varta)  when I started rebuilding- this lasted app. 6 months during which time I drove no where at all but developed the same faults as the previous battery- always discharged- wouldn't charge up to full capacity and discharged when left alone. I tested the current drain rate and found it to be 0... and also checked alternator charging and found that I had a stable 14.4V across the battery with the motor running. This  seemed high to me as I've had a motorcycle regulator problem resulting in battery death at just 14.7V in the past. However, I was assured that 14.4 was perfectly acceptable in this car and so I attributed my problems to a duff battery and blamed the suppliers... possibly wrongly. Anyway, assuming my problems were due to a bad battery, I bought a Lucas 075 unit and all was well. I finished the car, but even then I did find the battery discharged on occasion- once indeed whilst it was at the garage during its interminable wait for an MOT. However I drove the car frequently- amassing my 400 miles usage and then- yes you've guessed it, I left it for a couple of weeks or so and it was fully discharged again! The Lucas battery has started to loose charge just like my previous battery which I had assumed to be faulty. The only thing I hadn't checked was rectifier function so I tested for AC at the battery and and found none- again I have had rectifier failure on a bike in the past and AC will really brew up your battery quickly!

Well that's eliminated everything and yet I still have a problem. Here its confession time!!!! I am an idiot, a charming and enthusiastic idiot its true, but nonetheless an idiot.... it turns out that multimeters have an internal fuse that affects only the ammeter functions.... and yes, of the three meters in my possession not one had a working fuse! All therefore gave me the same reassuring but completely meaningless value of 0 for current drain and as all worked perfectly in every other respect I didn't realise I had a problem... however, replacing the fuses showed a completely different situation.

I turned off the ignition and radio, shut the doors and connected the meter in series with the battery. I found a current flow of nearly 140mA!


Apparently 50mA would be considered high so this was huge! The boot courtesy light was on in this test and turning that off reduced the draw by 36mA (I have an LED fitted not the usual festoon bulb).


This still left a current draw of over 100mA- and given my battery is only 50Ah, this would drain the battery completely in 500 hrs or  20days, probably making it impossible to start in rather fewer. This probably explains why I can't start the car if its left for a week or two! The only problem is that the only thing that should be drawing current under these conditions is the radio... and here a glimmer of recollection began to flicker!

I don't have a manual for this radio (Sparkomatic 309- if you have one and can send me a copy please get in touch!), so when I swapped my radio for the newer version, I had simply adopted the connections that were already in place in the car (see my post here). I know that the radio will have two live feeds, a switched live to run the actual radio and a permanent live to keep the internal memory and clock when the car is switched off. In my case I had found that both of these were already connected to a permanent live. I hadn't thought this would matter since the only things that should be drawing current when the radio is off are the memory and clock functions- both of which have only a small demand. Turns out this isn't entirely true- here I was shafted again by the dead cold hand of the LBPO- I really should have learnt not to trust anything he did, but without a manual I'm sorry to say I knew no better! Luckily I have a spare radio unit, identical to my own but with a duff tape deck, but I can certainly use it to check current draw.

I connected the old radio as  it was in the car- i.e. both lives to the battery positive and the case to earth- shock, current draw was 80mA!! Disconnecting the red/white wire saw the clock extinguished and draw fell to zero. This however rose to 250 mA when the radio was turned on. The clock remaining off!
Disconnecting the red wire saw the current draw drop to 6mA, regardless of whether the radio was turned on or off, and the clock remained extinguished throughout!

This then is the heart of the problem: The clock display function seems to require a Hell of a current at around 74mA! The display is only illuminated when both feeds are live and this is expected only to happen when the motor is running! The clock is not meant to be visible in a parked car with the motor off, yet this is how it was fitted in my case. This analysis has also allowed me to identify which feed is which and the permanent live feed  is the red/white wire; the switched the red. Later radios would have this permanent feed as a yellow wire so its important to realise that its different in these early radios.

I pulled a few fuses to check how the radio was connected. In my case both feeds drew power though a permanent live via fuse 3. Removing fuse 3 saw the current drain fall to zero!


The Lotus manual wiring diagram shows the permanent live should be connected via a purple wire to fuse 3 and the switched live via a yellow and green wire to fuse 18. I am hoping both of these wires are still in position even if unused. Thus as a minimum fix to solve this problem I need to disconnect the red wire (switched live) and reconnect it to fuse 18 through the yellow green wire which should already be in place- unless removed by the LBPO.

I removed the knee panels again and looked carefully in behind the radio. The purple wire was easily identified. It was connected through a double bullet connector to a brown wire terminating in an unused bullet and even bearing a ballast resistor. Similarly the green white wire was also present and terminated in an unused double bullet connector. The radio was not connected to either of these obvious connections . I was able to cut out the cumbersome extra wiring and rationalise so that the red/white wire was connected via the ballast resistor and brown fly lead to the correct purple feed and the red wire connected via a bullet to the correct green and yellow wire.

Purple/brown/ballast resistor feed connected to red/white wire as permanent feed.

Red switched live  connected to green yellow feed.

 I incorporated in-line fuses in both lines. This reconstituted the correct connections and the radio clock now came alive only when the ignition was turned on. Connected in this way, current draw had now decreased to 7.5 milliamps (pretty close to the draw related to memory/clock maintenance as determined in my bench test, and  battery charge life correspondingly increased to the order of 260 days!

Well having installed the radio I am struggling to find out how it shoyld operate.  There seems to be no manual for the installation and use of the radio although I will keep looking.  The company suffered a serious fire that destroyed many Te cords and brochures and as this was always a rare stereo in the UK the chances of finding a replacement are few.. . If you have one and can send a copy please let me know. In the meantime Im comparing mine with similar midels. .  This one at least gives some hints.