Grounding issue

T

terabytemc

Junior Member
I have a 1930 Coupe that’s been sitting for a year while working on restoration, I just tried starting it and it won’t start. I removed the instrument panel to check if I got all the wires connected to the ignition and amp and the speedometer cable sparked off the firewall and proceeded to get hot and smoke. Anyone have any suggestions?
 
Somehow the speedometer cable is hot. Verify with a voltmeter. If it is still attached to the speedometer look for a wire or connector that is shorting to the instrument panel. Remove the cable from the speedometer to see if the instrument panel is the source. If all this fails, look for another source like maybe some wire touching the cable lower down. An unlikely problem may be in the grounding of the battery in combination with a short somewhere, where the cable is acting as a ground, but this is very unlikely.

Make sure you have the aftermarket fuse that mounts next to the starter switch. See https://www.snydersantiqueauto.com/product.htm?pid=976199&cat=41746
 
I had a similar experience with a Model "A" that sat for many years. The ground connection of the battery was poor, so much so that when trying to start the car, many metal things got hot trying to complete the 200 amp ground circuit. Renew the battery ground connection to crossmember behind it. Also run a jumper cable from the battery's ground terminal to the cylinder block.
 

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It sounds like a short under the tank to me. Check the two wires from the terminal box to the amp meter. One may have compromised insulation and is shorting to the speedo cable outer casing. The speedo cable only run a short way down the tunnel under the tank but it's pretty crowded in there.
 
The most overlooked electrical connection on a Model A is where the battery ground cable attaches to the frame. It is out of sight and hard to get to. It could have been many years since it was last attended to. A resistance connection there can cause all kinds of electrical grief.

Remove the battery and disconnect the cable from the frame. On the frame where the cable attaches there is a raised boss. Clean all the crud and paint off it until there is bright metal. Wire wheel the end of the cable and the attaching hardware. Do this every time you replace the battery.

Tom Endy
 
i put an additional ground connection between my battery ground and the flywheel housing, made out of braided copper. My starter ran with twice the rpm afterwards. Very cheap upgrade...
 
I agree with NK. Look behind the panel gauge on the dash. My ammeter was touching the tank and smoking el productos!
 
So, I disconnected the speedometer cable from the instrument panel and the firewall placed it on the ground under the car. When the instrument panel was hanging by the wires it touched the gear shift and sparked, so it must not be directly related to the cable. I will checked the wires coming through the terminal box for any breaks in the insulation and will check the battery cable to the frame. Thank you for the suggestions.
 
So if the instrument panel is hot then there is a wire or connection shorting to it. Start disconnecting wires one at a time and then check with a voltmeter to see if the instrument panel is still hot. There may be an internal short at the ignition switch or ammeter. Remove things one at a time to find the short. The original popout ignition switch shorts to ground when pushed in so if there is a mistake in the ignition wiring that could be the source, for instance if the wire from the coil and the wire to the distributor are reversed.
 
Mod A s have a 90 y.o. ground path1 Trace it out sometime! It goes through a probably cruddy connection at the frame, down the frame rail, through the bolts at the motor mount, or down to the furthest front crossmember and a rusty rivet back to the engine block. Henry didn't know his cars would last 90 years so he didn't spend much time on the electrical connections. The fix for all of this is to get a copper cable and run it from the bolt that grounds the other cable to one of the starter bolts. You'll probably discover that 6V can really spin a 4 cylinder. engine over and you'll probably forget all about those hard to find 8V batteries and or a 12V conversion. BTW double eyed or double ended cables are sold at a Battery Warehouse. Other cars and trucks use then too. Good Luck!
Terry
 
Ok, so I sanded the frame under the ground strap (for good contact) even installed a new bolt, added an additional ground as suggested above, printed out a Model A wiring diagram and rewired all the wires to the terminal box. As a test I just had the instrument panel outside the car on the tank, no speedometer cable yet. Started car everything great, no melting wires (I melted the amp wire previously) no sparks. Great…all fixed. Not!!! Installed instrument panel back inside everything reattached, ready to go, as soon as I attached the battery cable my wire from the starter to terminal box melted. I will be purchasing the grommet for the ignition cable as suggested. I don’t understand for as simple a wiring system this is why is it giving me such a hard time.
 
Sounds like you have a dead short somewhere. I'm assuming you don't have a fuse in the system as mentioned in post #2.? Saves on wires.
 
Loosen the instrument panel and watch as you pull it back. Sounds as thought the key switch is grounding against the firewall. Usually just bending the terminals corrects that.
 
The way the terminal box was wired, they had to use flag terminals for things to fit around all the stuff in there. Some of the reproduction wire harnesses don't always have the flag terminals clocked for best fit. I've had to remove a terminal now and then to recheck. When they're soldered, it can be a PITA to get it all to work. Something that seems so simple can actually get pretty complicated. Even the coil power wire has to be just right to fit in there.
 
Check the terminal block on the firewall The reproductions have bolts for the threaded stock. Instead of being imbedded in the structure material they drilled a hole though from the back and indented the head of the bolts. they can easily migrate back and short out against the firewall.

What I do when installing one is make sure the nuts are tight on the bolts and the head of the bolts is well into the structure, then fill the back of the holes with JB weld and let it sit overnight. The JB weld is not conductive, and it will keep the bolts in place.

Tom Endy
 
I do not have the fuse yet, will be ordering that. I did notice the ignition cable has a plastic type sleeve on it that slides up and down, I was not sure what it was, maybe that is supposed to be down in the terminal box like where the grommet would be. I was planning on getting the dash wiring set, but currently just running 12 gauge strand after the 16 gauge that was already installed melted previously. Not using flag just ring terminals at his time. I did check the key switch, I don’t think it’s touching but the cover doesn’t like to just go on without a struggle. I did use a flex wire tube between the panel and the terminal box since I don’t have the loom that comes with the dash wire harness.
 
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Tom,
I like the idea of running another ground strap to the engine but how was the engine originally supposed to receive its ground, motor mounts?

Thank you,

George Knevelbaard
 
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