testing a wiring job without smoking the wires

[Tom Wesenberg]

I was asked a question yesterday and thought I'd offer some advice here to maybe save some new wires from going up in smoke.

On a freshly restored car, or rewired car it might be wise to leave the yellow wire off the starter switch and do a few checks first. With the key off, battery in and connected and all the wiring installed, just touch the yellow wire to the battery cable at the starter switch and see if it sparks. If it doesn't spark you can safely connect it to the switch, or fuse if you use one. If it sparks then unhook the yellow wire and lights/horn wire from the generator cutout. This will take the lights, horn, cutout, and generator out of the circuit. Now see if the yellow wire sparks when you connect it to the starter switch. If not then bolt it in place. Now touch the yellow wire to the cutout output terminal and see if it sparks. If no sparks then leave it connected and touch the lights/horn terminal to it and see if it sparks. If you see sparks you'll need to see if it's the lamps, or if it's the horn shorting out.

A quick touch will show sparks if you have a short, but will save the fuse and wires from going up in smoke.

A few of the more common shorts I've seen are:
1. Bad insulation inside the ammeter
2. Shorts in a repro brake switch
3. Shorts inside the headlamp connectors mostly on repro parts
4. Repro ignition switch terminals touching the gas tank
5. The small fiber insulating washers left off the horn brush holder screws and left off the terminals on slant pole coils.

[Jon]

Tom, thanks for the advice. I'm planning on rewiring this winter. Do you have a preferred source for wiring harness?

[Tom Wesenberg]

Since my 28 and 29 have fluted headlamps I purchased my headlight harness from Sacremento Vintage Ford. They make the harness in house and I like the quality. Rhode Island Wiring also has excellent wiring and many guys who go for points use them. I don't know of any supplier that has a particular problem with the wiring, but so far I've only seen the harness from a couple suppliers. Try to use your original contact plate and light switch, as it has the best motion. Make sure the wiring terminals are soldered to the wires.

If you use a repro contact plate in the light switch I have sanded the edges of the dimples to give the switch action a smooth motion. I also like to use a little Vaseline on the contacts.

[MrTube]

Tom,

Wouldn't it be wise to simply ohm out the circuit before connecting power to it as well as use a very low rated fuse like 15A the first few times running the car? This was the procedure I used anytime I did electrical work on the "A".

[Gary Gregory]

Good advise Tom. I'll be wiring my 30 Coupe very soon....I hope !

[Tom Wesenberg]

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Originally Posted by MrTube

Tom,

Wouldn't it be wise to simply ohm out the circuit before connecting power to it as well as use a very low rated fuse like 15A the first few times running the car? This was the procedure I used anytime I did electrical work on the "A".

Yes, but for a quick check without an ohm meter you can touch the wire to check for sparks and not blow a fuse or burn the wires.

Many guys don't have an ohm meter or know how to use one, so touching the wire will work for them. I always recommend using an analog multimeter with the Model A and the Sperry SP-152A is an excellent meter and cost less than $20 at Menards or online. Here is one link to a Sperry shipped to your door for only $14.90.

http://www.ebay.com/itm/W-Sperry-Mul...item2eb552c198

[RonC]

Creating sparks on a Model A is inviting disaster to burn down your garage or worst. I would always add a fuse and if the fuse pops when you connect the battery, at that point I would search for the problem. fuses are cheap.

[MrTube]

I don't know Ron,

If your "A" is so saturated in gasoline that its producing enough fumes to worry about that I don't want to ride in your car

[BILL WILLIAMSON]

A good idea is to put a circuit breaker into your fuse holder for protection, Littlefuse makes ones that pops into a fuse holder and I think that G.M. also makes one that does the same. Use a 30 amp.

[Ned]

Take a small 6 or 12 volt bulb and attach clip leads to both terminals. I like to use a 12 volt bulb used in modern car dome lights. With everything turned off, hook one lead to the starter post and the other to the disconnected yellow wire end. It should not light up unless you have a short to ground somewhere. The bulb limits the current to a safe level that will not damage the wiring. You can also use the bulb to tell when the points open and close, when you have voltage across the points, etc. Unlike a meter, you don't have to be able to see the display, all you have to see is the light.

[Richard Wilson]

Thanks Tom. A quick word about your #4 problem. It happens not just on new installations. I had a man in my Model A club with an ignition switch becoming loose in the dash panel after driving his Model A for a number of years. When he would turn the switch off or on it would move. Finally it rubbed through the paint on the gas tank, shorted out and burned up the wiring harness while the club was on a tour through the Smoky Mountains National Park. Luckily I had enough spare wire in my tool box and was able to rewire the car for him while sitting on the side of the road after finding the problem. All of that fire and smoke was very scary!

[columbiA]

I always use several layers of tape on gas tank behind ign switch & use 30 amp breaker at starter . I dont like the fuse holders that the vendors sell.If the clip for the fuse overheats it will have little or no contact with the fuse & could possibly burn out the generater.

[Tom H.]

Originally Posted by RonC

Creating sparks on a Model A is inviting disaster to burn down your garage or worst. I would always add a fuse and if the fuse pops when you connect the battery, at that point I would search for the problem. fuses are cheap.

Ron, if you have a short I think it will still spark when you hook up the battery, even with a fuse.