Electrical Expert Needed ASAP

I am no electrical expert but I can wire up a car off diagrams. I have an electrical problem and need troubleshooting help. Please read carefully for all I have done so far. The car is a 1968 Hemi Dart clone and has been driven about 200 miles so far. The car ran fine until two days ago when I went to start it up. The fuseable link blew going from the starter relay to the bulkhead which sends power to the ammeter.gauge. The opposite side of the ammeter uses common power to the Alternator Battery post, the ignition switch battery post, the headlamp switch, horn relay and two fuses in the fuse box according to the diagram.

1) I had the alternator tested for grounding and it checked out fine.

2) I used test light between the bulkhead and the starter relay where the fuseable link would go, and no light, fine.

3) Turned the ignition switch to on position and test light went on, meaning a ground somewhere?

4) Disconnected the wires one at a time to feeds, first the alternator, then headlight switch, horn relay. Test light stayed on.

5) No blown fuses in fuse box so that is OK.

Question, can the ignition switch be bad? Is there a way to test it?

Where do I go from here?

The complete wiring system was checked for breaks or bad wiring before installing into the car. Everything was working fine. The car does have a MSD ignition installed if that means anything with the problem.

Car will start right up with new fuseable link, only for 5 seconds, at which time the link blows.

Wire going from starter relay is 10 gauge and fuseable link is 16 gauge. Other side of bulkhead is 12 gauge per diagrams.

Any help would be appreciated to solve this problem.

I HATE ELECTRICAL PROBLEMS.

Are you saying the oil pressure light has two 12v sources? I seems to me that the test light going on when you turn on the ignition switch just means you are sending power to the msd.

According to the electrical diagram the wire from the bulkhead/ fuseable link then goes to the ammeter The other side of the ammeter is common to the other connections. This is looking at the diagram. What I am saying the car was working fine until this issue arose.
Does some have another diagram for a 1968 Dart they can look at.

The alternator wire goes to the ammeter, NOT the oil light. The other side of the ammeter goes to fusible link and on to the starter relay and the battery. The oil light picks up power from the dark blue with trace from the ignition switch.

You are correct it is the ammeter not the oil gauge will change in top post. The diagram is listing between oil gauge and ammeter. Thanks.

More input info. If I open the door the test light will light up. I removed the test light and put a jumper wire between the starter relay and the bulkhead, where the fuseable link would go and the dome light will go on. How can it be a positive and negative connection. Makes no sense to me.

if you don't mind blowing another fusable link, can you see if it blows with just the car in run vs actually running?

and when it blows are you just at idle? or did you rev the engine any?

If no fuses blow, then you can probably eliminate those circuits, but for fun in case it is a cumulative issue, could you pull all your fuses as well.

Here is the order I would go.
pull all the fuses.
put the car in run but not started.
If it blows then, you know it has to be an accessory circuit that only gets power with the key and the alt has nothing to do with it.
If it doesn't blow I would start the car and see if it still blows.
again, it still narrows down your circuits to check either way.

Placed new link in, turned key to run position for 20 seconds nothing happened to link.

The dome light is the ground when you open the door. It pulls juice from the battery. All test light is showing is that you have a complete circuit. You need to pull the courtesy light from the circuit. dome light, glove box and trunk lights as well as any other interior lights other then those operated by the headlight switch and dash dimmer.

Unhook the battery, disconnect the main wire to the alternator, tape it up so it will not short out on something , reconnect the battery start up the engine, You may have an intermittent short in the alternator that only occurs once it warms up a bit.

This is not a good way to test for shorts to ground in the main circuit!!!


This is not likely but definately possible. Same concept but more likely its in the 'ignition' or 'accessory' circuits.
I put those in quotes because those are really the feeds for all power that gets switched on with the key turned to RUN.
Maybe slightly more likely is a loose battery plate. When the alternator is producing power the battery sucks it for all its got. And if its a bigger alternator, like a '60 amps' then after a couple minutes of 50 - 60 amps, the link melts.
This would show as the ammeter pegged to the charge side.


This makes no sense.

The fusible link protects against battery shorting in any of the unprotected circuits.
Most important it protects in case the battery shorts to ground.

If there is a ground short in any circuit after a fuse or breaker, those will fail long before a 16 gage wire melts).
That 16 gage wire can handle all normal power needs for the car if you have to limp home on battery power.
Even 30 or 40 amps for short periods of time will not degrade it.
Just don't be putting 30 - 40 amps through it continuously. But that's not the issue here.

There's a couple ways to safely hunt for the short with the battery connected.
One is to install a circuit breaker where the fusible link goes. Chrysler suggested their techs use a flasher unit.
Another is to wire up a '12 V' light bulb and place that where the link goes. (Test light, but not internally battery powered)

With the battery disconnected, you can try a continuity tester. This can be a battery powered test light light, or a multimeter with resistance or continuity measuring,

Lets go over the information so far.
Dome light: As Lusk said, the door switch completes the circuit to ground. This circuit is hot all the time, but is protected by a fuse.
Key in Run: This makes both the ignition 1 (run) feed hot, and the accessory feed hot. Accessory feed goes to fuse box, windshield wipers, and a few other 'accessories'
Battery installed: This makes the entire main circuit hot all the time, ( plus the feed to the starter motor).
If there was a short in the alternator output wire, or the wire leading to the key switch, or to headlight switch B1 terminal, the fusible link would have melted as soon as the battery went in.

An observation of the ammeter would be a useful clue as to where the short is located.
http://www.heritech.org/cuda/Charge2.html

Below is a basic late 60s A-body scheme:
MSD 6 traditionally was switched on by removing the power wire from the coil and connecting to the MSD 'on' wire. This must be isolated from the coil and ground.
The MSD 6 often drew its power by connecting at the battery positive or the starter relay stud. Alternator output stud would be OK too.
If you're doing early MSD, like the 505BC, I'd have to check if the wiring is the same.

Jump a wire from battery output stud back of alternator and connect to battery stud of starter RELAY.
Make sure you run an inline fuse or fusible link at the end of the wire at the relay.
If everything works normally the ammeter gauge is NFG.
You can run the car like this forever if you do not want to pull the cluster to replace ammeter and run an aftermarket 12 volt guage in the car
Hope this helps

Do you know how the ammeter works?

Its metal plate connected to two insulated studs.
The needle movement is basically magnetic and carries no current to speak of. It deflects in proportion to amount though the metal plate.
While the connections can fail, the movement can fail, and some years/versions are more prone to issues, if there was a short to ground in it or any wiring to or from it, the link would go to smoke as soon as the battery was hooked up.

If no current, Fuseable link OK with key off, then the ammeter, constant power circuits and alternator output circuits are not causing the problem.

Check in the ACC (accessory) position, and if no problems, then the problem is likely in the engine wiring harness. If the fuse blows in the ACC position, issue is in the Accessory interior wiring, check ignition switch to fuse block.

If problem only in RUN position, check connections at alternator, regulator, ballast resistor, coil, electric choke, any other item powered off the engine run circuit

Just as a quick check I removed the battery wire off the alternator. Started the car and everything worked fine. Ran for two minutes and no blown fuseable link. Had the alternator tested again and they told me it checked good.

But with the alternator connected it will blow the fusible link in substantially less than 2 minutes running?

Either the alternator is warming up in use and shorting, it's rare but possible, or your wiring is chafing/rubbing somewhere as it vibrates and shorting out.

Have you another, known good alternator to swap in? Closely inspect the heavy wire from the alternator output and make sure it has no bare spots.

As for the parts store test, I get skeptical about them myself.

I had an alternator check fine on the parts store tester and, as noted, it was shorting out after operating for awhile. Took me a couple days to figure it out. If your wiring checks ok, try a reman alternator.

one other possibility, have you measured the voltage when running with the alt hooked up?
I had a bad connection to the VR one time and it vaporized an inch of 10 gauge wiring and melted about 2 inches of insulation on either side.

normally an alt will only put out as much as you need, so a dead short would be the normal way to blow the fusable link.

but as you already determined, it didn't blow with the car in run only, and it didn't blow with the alt removed.

it could be as surmised a bad alt that has an intermittent ground. Or it could be a bad charging system.
in my case it was a bad connector, and it caused a serious over charging condition. It was a long time ago, but I recall the guy saying it was putting out over 100 volts.
It was before I understood electrical and someone converted the car from the old 40 amp alt to 100 amps and the 2 field vr.
The connector they used was poorly crimped and not weather protected.

I would see what your voltage is while running and see if that could be a cause before swapping out alts.

May have found the problem. The tachometer was jumping a little after the first burnout. Then went dead after starting again. I reconnected the fuseable link with the alternator. Then diconnected the tachometer both power and signal feed. Started the car and ran it for a few minutes. Everything seems to be working fine. It is a new steering column mounted Autometer Street Tach. It only had about 8 hours of drive time on it. Makes no sense that the 16 gauge fuseable would blow before a 18 gauge tach wire. If this turns out to be the problem I will be contacting AutoMeter to see what they will do for me.

that doesn't seem likely.
I have never heard of a tach doing anything like that.
At worst it grounds out the ignition system and you can't start the car.
plus I am betting power to the tach is fused right?

My gut is still telling me there is an issue with the alternator. But I had it tested twice by 2 different shops and they said it was good. The unit is a Powermaster 90 amp built out of the old round back case. A buddy had one on his car that failed him on the road 3 times and the alternator still tested good. He replaced the alternator with a new one and never had a problem again. I believe the spike fried the tachometer.

The FSM has some pretty decent alternator T/S guides and rebuilding your own isn't too bad.

Parts source

You might be having an intermittent full field going on, does the ammeter peg out at all?

I agree with Sniper.
The ammeter will often reveal alot.
It must be observed in conjection with the situation as it reacts to current flowing.

Having a handheld voltmeter will also help considerably.
Measurements from it are also situational. For example, measuring the voltage at the alternator output stud ( to ground ) at slow idle might be different than fast idle or higher rpm.

Using the ammeter together with voltmeter readings can be very powerful combination for troubleshooting.

I don't know what Powermaster has done to get a roundback to produce 90 amps,
Checking the basics of any alternator are pretty easy. Opening up a roundback one must be a little more careful than a squareback, but neither are difficult. Keep the stator together with the rectifiers and nothing will get broken. Leave the pulley on. No reason to remove it unless the rotor or the bearings on that end need replacing.

Concur. Must be some super duper stator.

OE alternators were typically 37amp, 50/60 amp for A/C cars. When I rebuilt my 70, I replaced the OE stator with a 50amp NOS (to help supply a few more gizmos in my RR).

Everything seems to point to an intermittent alternator issue. Try another reman unit.