Battery hookup = smoke, electrical experts needed

Drew N. Minnesota

Drew N. Minnesota

Member
I had high hopes I was going to be able to get the AA started today because my mother-in-law and father-in-law were there(it was his dad's truck). We had a nice lunch and my kid's were hoping for a ride. I warned them it might not happen and now, in hindsight, I should have hooked the battery up previously to get the issues resolved first. The battery, wiring and dash light are all new. When I hooked up the battery, we noticed a couple of things:
1) the dashlight came on
2) the brakelight came on
3) the ammeter showed a discharge of around -10 or so.
4) by the time I got the battery disconected the wire insulation was smoking a bit at the stop light switch and at the light switch body at the end of the steering column.
I'm a novice when it comes to the electrical system of the model A so any advice is welcome. I'm wondering if I had the wires to the brake switch on the wrong terminals or perhaps I will need to rebuild or replace the switch.
Thanks
 
The Ford Model AA truck is a Positive ground system. The Pos. cable will go to the frame, and the Neg. will go to the starter. Many folks that are used to working on newer cars can get confused when working on an older car or truck with a Pos. ground system.
 
The electrical system is pretty simple and there are no fuses, so you might consider adding a fuse or two to protect the wiring from burning up.

It sounds like you have something shorted to ground, which is positive on the battery, so maybe I should say "short to chassis." When you connected the battery cable, did you see a big spark? With everything turned off you should see no sparks when connecting the battery.

You'll have to isolating different parts of the electrical circuit, starting with everything floating, and briefly reconnecting the battery. No sparks is good.
 
The dashlight must have been left in the ON position.

The brake light switch must have been stuck in the on position. Check that the pedal is fully retracting--if not, may need to add a helper spring. Otherwise, the switch may be bad.

It doesn't make sense to me that onlyl drawing 10 amps should smoke the wiring at the locations mentioned. THose wires can easilyl handle 10 amps. HOWEVER, if there is a weak contact or a short to ground, that would smoke, but--again--a short should pull a lot more than 10 amps.

FIrst thing to do is disonnect the brake light switch and see if you're ok otherwise.

Steve
 
Repop stoplight switches are notorious for shorts. Disconnect the hot wire and see if the ammeter draw goes down to an amp or so reflecting the dashlight current. Then see if you perhaps just have the dashlight turned on instead of off. If not, troubleshoot that.

Joe

On edit: Steve types faster than I do.
 
Hooking it up backwards(negative to frame) would not have caused any smoke, anyway.

try disconnecting as many circuits as you can(perhaps at the terminal box), hook up the battery(hope there is no smoke), and then re-connect things one circuit at a time, fixing an problems as they become apparent.
 
It didn't seem like a big spark when I hooked up the negative cable, but it definitely sparked. Also, it may have been more than 10 amps, my head was stuck down by the floorboards disconnecting the battery so 10 amps was secondhand information.
I'll try disconnecting the brake switch next time I'm there. Can someone tell me how to turn off the dash light - I've never used one before so maybe that was just in the "on" position.
 
If it's the same as a standard model a, push it in the light and turn it left. Should pop out some.

Maybe time for a new harness. If you have the ignition on and nothing else on (lights) you should not be pulling more then a negative 6 from the coil.

You have a short somewhere (brake light), that would be my guess.
 
Like mentioned above, I would get a fuse put in your system so you won't burn up. You can get these from any vendor.

And I think the idea of taking off the wires to the brake light switch is a good idea and then try to connect the cable again. I had a brake light switch short out, it blew my fuse. Lucky to have the fuse.
 
I disconnected the brake light switch and and turned off the dash light and it was still drawing 5 amps when I connected the battery. I think it must have been 15-20 amps with the brakelight switch connected, not 10 amps like I stated earlier. I disconnected the yellow wire to the starter and it wasn't drawing at all. The insulator gasket on the starter switch seems to be be original and it appears to have shrunken and disintigrated over time. In addition to getting the stoplight switch repaired/replaced, I will order an new starter switch gasket and a fuse. I've read that A & L makes good ones for the '30-'31's but do they also make quality switches for the '28-'29's? I'm disappointed to see that no one is making the innards of the stoplight switches for repair.
 
Let's see step by step,remembering that the key only turns off the ignition and has no control over anything else. All lights and horn will work with the key off.

Drew N. Minnesota said:
When I hooked up the battery, we noticed a couple of things:
1) the dashlight came on - the dash lite was left on when installed - normal operation when battery is connected.
2) the brakelight came on - this is not normal and as mentioned earlier the repro switches are a problem. But since the brake light bulb lit up there can't be a short. You see, the voltage comes from the switch assembly at the base of the steering, goes to the brake light switch, out to the bulb and then to the chassis, if there was a short, the voltage would go to the chassis short of the bulb and the bulb would would not light.
3) the ammeter showed a discharge of around -10 or so. With a new amp meter I would not trust it for a true reading.
4) by the time I got the battery disconected the wire insulation was smoking a bit at the stop light switch and at the light switch body at the end of the steering column. OK my guess is that the problem is in the repro light harness switch or the headlight connectors in a head lamp. Especially if you are using repro sockets or connectors.
Click to expand...
 
Before ordering parts you might want to consider a master kill switch. It's a lot quicker than trying to get access thru the floorboards to disc batt cable. Mine is mounted under the front seat, very convenient and out of sight.
Paul in CT
 
>> "But since the brake light bulb lit up there can't be a short."<<

It is true that since those lights lit there isn't a short in that circuit. But lit lights won't cause a wiring harness to smoke/burn. Smoking wires indicate a large current flow. So there's probably a short to chassis somewhere.

 
"OK my guess is that the problem is in the repro light harness switch or the headlight connectors in a head lamp. Especially if you are using repro sockets or connectors."
Mike,
When I had the stoplight switch disconnected I also tried the headlights and they worked on both low and high beams. Would that rule out a short in the headlights? What should I check next?
Also, I took apart the stoplight switch and the insulator was cracked with a part of it floating around. Has anyone taken the insulator from the repros and tried it in an original or used some other insulator material?
 
Disconnect the battery first. Take the smaller wire off the starter that feeds the electrical system from the battery. Insert a small 6V bulb if you are a 6V system (12V bulb if 12V) which you have connected alligator clips in series with the connection from the electrical system to the starter terminal. The other wire on this terminal goes to the batery. Reconnect the battery. You can now either remove all the connections from the terminal box and replace them one by one or start pulling them until the light goes out. When the light goes out you have found your problem. Do not forget to turn off the dash light and all other lights. With everything off on a properly operating electrical system the bulb should be off. After you have found and corrected the problem put a fuse in the system. With a fuse there will be no burnt wires.
 
When troubleshooting electrical problems, I make sure there is a starter-mounted fuse, and I also have a 20AMP (lower values also available, but 20 amp seems to work best) self resetting breaker that I picked up from a camper/trailer supply place that I snap into the fuse holder.. I also keep one in my travelling toolbox.. Using it keeps from eating up so many fuses.. If there is a short, the breaker warms up and pops off, let it cool and it self resets :)

Saved me a lot of headaches so far!
 
Last edited:
You must log in or register to reply here.
Back
Top