MTFCA Forum

I have a 26 coupe that has been restored. Lately if I don't run it for a week or so, I go to start it and the battery will nearly be flat. The battery is relatively new 1.5 yrs old, I was having problems with the cutout sticking so I changed it to a diode one. Yesterday after a 3 mile run, I tried to check out what's running the battery down. What I did was remove the hot(battery) wire from the terminal block and using a multi-meter on 200MA I checked for a current draw between the hot wire and all the screws on the terminal block, nothing. I checked the cutout it's OK. Question is was I checking it properly or should I be looking for something else. Thanks, any suggestions would be greatly appreciated.

If your ammeter shows a normal charging pattern when driving (3 to 5 amps) and you drive the car enough to recharge the battery after starting and your diode shows good, you probably have a bad battery. Dirt and acid residue on top of a battery can cause it to slowly discharge. If the battery is clean, I'd disconnect the negative cable and put an automatic charger on it overnight, then let it sit for a week disconnected, and then see if it will perform as it should. If not, it is defective. Even a small dash light bulb would run a battery flat over several days. It's possible for a bad terminal block or ignition switch to leak current to ground, but not likely. If you have any electronic devices in the car, they could be slowly discharging the battery. The best test would be to fully charge the battery, then let it sit, disconnected, for a week and see how it works. Load tests, etc, can be inconclusive. Batteries do fail prematurely, which is why they still have pro-rata warranties. A battery that has been exposed to freezing weather when discharged can be severely damaged, and a battery that has sat for a period of time in any weather when discharged can be damaged. Persistent overcharging can damage a battery, and AGM type batteries may be more sensitive to overcharging damage than wet cell types.

There’s probably a couple ways to do it but I have used a test light between the disconnected ground cable and the battery’s ground post. If the light comes on something is drawing power. Then go to the fuse box or in your case a terminal strip and remove the fuse/terminal one at a time and see what one makes the light go out. Make sure your battery is fully charged before you start.

One thing which can cause a discharge would be a terminal strip on a steel firewall. If one of more of the screws is too long and comes in contact with the firewall. If it happens to be the one which you lifted off the wire, the screw would be loosened when the wire is off and at that time would not contact the firewall. I would suspect that the car is just not running long enough to recharge the battery after starting. If you have a strong arm, try crank starting the car the first time you start it when cold. After it warms up, the starter will not use as much electricity to start it. Usually just a bump.
Norm.

I'm with Txgoat. I would suspect a bad battery. I have a Shumacher 6-12V battery slow-charger that will tell me if the battery is bad. It wasn't expensive.

I never park any of my collector cars with a connected battery. George

Many years ago there were new terminal strips being sold that were partially conductive. Just to be sure you don't have one of those still floating around, push your ohmmeter leads into the black "insulation" material on the terminal strip. Anything other than "open" may be what's pulling your battery down. In my case, it took about a week to kill the battery...

I purchased a cheap load tester from Harbor Freight many years ago. Best $20 I ever spent. Takes about 2 minutes to check any battery. It will also check the charging system. It least you would know if the battery is not up to snuff!

You may a short some where in the wiring. When I restored my 1919 Roadster I bought a new terminal block from Snyder’s. New wiring and etc. after a few days the battery would be almost dead. Charged it again and again in a few days it was almost dead.
Checked and checked and finally to a reading between the terminal bock and the metal firewall and it had continuity!!?
It turned out the rubber terminal block was hot all the way across. Snyder’s found out that the supplier had sold him terminal blocks made from ground up tires that had steel wire in them. He replaced it and changed suppliers. They have always been a good supplier for me and will try to help if they can.
You could also have a bad battery. That’s happened to me on my T’s when not using a trickle charger on it if I don’t drive it often. Batteries do have to be used fairly often for good life expectancy.

dunoon wrote: ↑

Sun Nov 14, 2021 10:08 am

.....I was having problems with the cutout sticking so I changed it to a diode one. Yesterday after a 3 mile run, I tried to check out what's running the battery down. What I did was remove the hot(battery) wire from the terminal block and using a multi-meter on 200MA I checked for a current draw between the hot wire and all the screws on the terminal block, nothing. I checked the cutout it's OK. Question is was I checking it properly or should I be looking for something else. Thanks, any suggestions would be greatly appreciated.

To start with - it sounds like you were having battery issues before you changed the cut-out to a diode, so maybe the solenoid cut-out sticking wasn't the issue. Hard to tell.
Some instructions on how to test a diode https://www.electronicshub.org/test-a-diode/
Something to be aware of: It is natural for continuity to exist between the generator post and ground (that's why there is a cut-out). Now here is a subtle difference between the solenoid & diode cutouts with respect to continuity. When the engine is not running and the solenoid is not sticking there will be no continuity across it. However, since the diode is a voltage blocker there will be continuity from the generator post to the battery post but not in the reverse direction when you switch the probes (if it is working properly). So I would expect you to have continuity (but no current draw) from the hot wire to screw #3. With the switch off and all wires connected, there isn't much chance for a short. Where did you get the diode/cutout?

dunoon wrote: ↑

Sun Nov 14, 2021 10:08 am

and using a multi-meter on 200MA I checked for a current draw between the hot wire and all the screws on the terminal block

I hope you started with the 10 or 20A range first. Any normal electrical load in a Model T, if switched on, will blow the 200mA fuse straight away - and thus give a zero reading. It's safer to just use a low wattage light bulb for this test.

If you have the traditional lead acid battery with the 3 caps on the top, be sure the fluid level is above the plates. If it is low add distilled water. Another tool which is handy is a hydrometer. It has a bulb on one end and a tube to insert into the battery. A portion of the fluid is drawn into the hydrometer which will test the specific gravity of the fluid and give you a reading as to the condition of the battery. After using, be sure to wash out with water and don't come in contact with the acid solution.
Norm