Electrical Problem

reek29

reek29

Member
I have another problem I need help with. It's driving me nuts and I'm gonna relax now and ask for help.
I have a '29 CCPU that is stock except for an alternator (6v) and fuse.
After idling for 10-15 minutes, the fuse blows. Attempts to replace the fuse only end up with more blown fuses. I disconnected the wire from the alternator that feeds lights, horn etc. and problem goes away. Also, with all electrical accessories off, when I touch the disconnected wire back to the alternator, I get a spark. The problem is not in the ignition, because with the wire disconnected, she starts and runs fine. Also, the fuse has never blown while driving. Only after warming up at idle. Once she cools down, I can replace the fuse and everything is normal. I checked the horn and headlight wiring (the headlights are direct wired, not using the spring loaded sockets) and can't find a thing wrong. I wiggle all of the wires and can't get the problem to repeat. Only after idling for an extended period.
Anybody seen this "gremlin" before?
Thanks in advance for your help.
Rick
 
Hi Rick,

Just a couple of thoughts...

Which fuse are you talking about? Do you have a single main fuse, or a separate one for the alternator wire?

Have you noticed if your ammeter suddenly jumps just before the fuse blows?
 
Do you have an auxillary ground strap from the frame ground strap(same bolt) to the top of the passenger side of the transmission tower? Bob
 
You might even have a faulty headlight bulb or socket. How about the brake switch and tail light. I've seen faults in both of them also.

Leave the lights connected and remove and tape the two wire ends for the horn and see if you still have a problem. At least that would eliminate the horn.
 
Yep. Something has a short. Check the wire to the tail lights. look for any rubbed bare spots touching the frame. Could be a pigtail wire in the tail light barely touching the tail light housing. Could be the starter switch on the starter shorting with vibration in the car. Headlight wiring at a connector having a little copper exposed and vibration causing the wire to touch metal blowing the fuse. I've also seen replacement on/off switches having bare terminals touching the gas tank behind the dash causing a short.
 
This is important: exactly how does the fuse blow? Can you see if the fuse wire in the fuse actually blew, or did the fuse's endcap lose its connection with the fuse wire (impossible to see)? Sometimes a fuse fails because a poor connection with its holder results in overheating and its internal connections coming undone--the fuse wire, per se, never pops. The quick fix is to remove the fuse and squeeze the gripper contacts closer together to give a tighter connection; better fix is to install a better fuse holder. This wouldn't be so much a problem going down the road either because increased vibrations are giving a better contact OR the alternator is handling the load and not so much current is coming out of the battery--maybe.

If the fuse wire really blew, then there's a short somewhere, and you must be using slow-blow fuses.

Steve
 
what type alt? one wire, 3 wire, or one with seperate regulator? alttenators are funny critters, they do most of the charging at low rpm's unlike generators which do there charging at higer rpm's, if you do have a short and your battery is low the alt will put out a lot of amps at idle, could be why you blow a fuse there and not runnibg down the road, discount the ground, put an electrical trouble lite checker between the batt and batt cable, if you have current flowing the lite will come on, discount one thing at a time, like one head lite, tail lite, brake lite till the lite goes out that is where the problem is, if things are fused just pull one fuse at a time till you find what is causing the spark, you may be able to just go round touching things, the one thats warm will be the problem
 
ford1 said:
what type alt? one wire, 3 wire, or one with seperate regulator? alttenators are funny critters, they do most of the charging at low rpm's unlike generators which do there charging at higer rpm's, if you do have a short and your battery is low the alt will put out a lot of amps at idle, could be why you blow a fuse there and not runnibg down the road, discount the ground, put an electrical trouble lite checker between the batt and batt cable, if you have current flowing the lite will come on, discount one thing at a time, like one head lite, tail lite, brake lite till the lite goes out that is where the problem is, if things are fused just pull one fuse at a time till you find what is causing the spark
Click to expand...


With all due respect alternators produce higher output at higher rpm's in regards to current. They simply are able to produce a much higher output at low rpm then your typical generator due to the regulator.

Unrelated to the thread, the main difference between a generator and alternator is an alternators power is pulled from the stator via rectifiers while a generators power is pulled via brushes from the rotor.


As I believe others have asked, we need more details on where the fuse is that keeps blowing. I also agree with Tom's process of elimination.
 
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All that you are saying indicates a very strange phenomenon. It could be that the regulator circuit in the alternator is not working properly. Another thought is that you may not have a good ground on the battery. The most overlooked electrical connection on a Model A is where the ground cable from the battery connects to the frame. It is out of sight, out of mind, and out of reach. You have to remove the battery to get to it.

Disconnect the cable and put a sanding disk on a drill motor and sand the boss on the frame where the cable connects until it is bright shinny metal. It may have 80 years of corrosion, crud, paint, powder coating and what not on it. Also wire wheel the cable and nut & bolt.

You really don't need additional ground cables strung around the car. A lot of people think they are needed. They don't hurt anything, but Henry Ford didn't think they were necessary and neither do I, even with float-a-motor engine mounts and with the engine splash pans missing.

Tom Endy
 
I do have only one main fuse that, when it fails, blows the element. The ammeter does jump to the negative when the fuse blows. I don't have an auxillary ground. The fuse blows when all accessories are "off". I'm pretty sure that it's not the ignition switch touching the gas tank cuz the fuse only blows when the accessories are conected to the alternator. That's also why I don't think it's the starter switch. Don- I did have problems with the headlight sockets. I ended up wiring the headlights direct. I don't use the spring-loaded connector socket anymore.
The frustrating thing is that the short doesn't occur when you are watching for it. Only after idling. If the lights aren't on and I don't have my foot on the brake...hmmm...bad brake light switch, maybe?
 
Curious problem. The first question in toubleshooting is what stops working when the fuse blows. IN what circuit is the fuse? Sounds like it is in the light/horn circuit only? Since it only happens at idle, is the alternator charging at idle or drawing from the battery? Next question is what size is the fuse? Check the fused circuit with a voltmeter when cold and working, then a continuity tester when the fuse blows. Something is shorting, so work forward from the fuse to find and eliminate the path to ground. Eliminate the horn first, it is separately wired and easiest to check. Just disconnect the horn wire and see if the fuse still blows. Then disconnect the all the lights one at a time, including tail lights and stop light switch and everything else in the circuit until you find what goes to ground. I also agree with Tom re ground, 90% of electrical problems are ground related. However, unlike Tom, I have the heavy battery wire to the trans top with a wire braid to the original chassis ground point. Whichever you do, grind out the 80 years of crud and get a good ground first even before you start checking for continuity because a lousy ground will mess up those readings. Just as a thought, I am wondering if there may not be a problem like corrosion in the rotary light switch. Make sure all contacts everywhere are clean and bright. Good luck and keep us advised.
 
If you remove the alternator from the circuit and can start the car, let it idle, drive it around, turn on all the lights, and it does not blow the fuse, you don't have a short anywhere. The car will run just fine without a generator or a battery, until the battery goes dead. If when you connect up the alternator your fuse blowing problem returns the fault has to be in the alternator or in the battery grounding.

Tom Endy
 
Tom's idea is a good one to eliminate the alternator as the problem. Disconnect all wires from the alternator, join the wire from the ignition wire side with the wire to the horn/lights with a nut and screw, and see what happens. If the fuse does not blow and all works well there is no short as Tom says and the problem is probably the alternator. If the fuse blows, it is not the alternator (which is disconnected) but there is a short somewhere. Disconnect the horn/light wire and see what happens. If the fuse then does not blow, the problem is in the horn/light circuit, which is what I suspect from your description and I think it would be a short in that circuit. But do clean all ground and wire connections before even starting.
 
Is this the fuse that mounts on the starter that moost vendors sell? There are several different styles, if this is the fuse which one do you have?
Paul in CT
 
Like Paul in CT, my first suspect is the fuse holder. If it's the type located on the starter I have seen several of them that were junk and would short and blow the fuse. If that's the type you have I would remove it and carefully inspect it for solid connections.
 
If a short circuit is causing the fuse to blow check each accessory. Shortly after staring my A for the first time the fuse blew. My original dash light was the culprit. The next time a fuse blew I traced it to the reproduction brake light switch. Good luck.
 
Don Turley said:
I am not talking about the spring loaded connector socket at the bottom of the headlamp housing. I am talking about the bulb sockets.

Don Turley
Click to expand...
As per Don's comments I had repro bulb sockets in my coupe and was traveling home from a show in a light rain with lights on when the fuse blew and everything died. When I looked at one socket the three contacts had large heads and loose fitting pins allowing the contact to short out on the socket base. Apparently it grounded out due to vibration and the rough road. I took them apart and hand ground the 3 contact diameters smaller like the originals and haven't had the problem since. The repro socket pins don't slide and fit as closely as originals.
 
if you have a pop out, pull the cover off the terminal and make sure that the wires clear the pop out cable,
 
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