Have a 68 RR with the Alt gauge wires got hot and overheated into the dash harness. Is there any way to bypass these wires in the harness or is a entire new harness in order . Thanks

Check out the MAD Electric upgrade.

I would replace the wires/terminals that were affected & it sounds like the poor connection that overheated was at the ammeter. get the new stuff clean/tight. Nachos' bulkhead parallel bypass is a very good seperate move (but proactive) if the problem was at the ammeter. Elim the (2) pairs of male/female brass terminals for the main in/out wires & solder in 2 lengths of wire in the drilled out cavities. Not sure if too much heat from soldering will mess up the fusible link so use clip on heat sinks or just be carefull with the heat travel. leave ~5" of wire length(s) behind the rear bulkhead half under the dash so if you have to seperate the bulkhead in the future you can pull the front half out/forward. clean the rest of the brass terminals while you have it apart. easy bristle brush the male ones & use a spare male terminal on the female ones, a spare or NAPA 725147-99 cents for new. spray em clean with brake kleen then see a computer/electronics store for a recommended conductivity enhancing paste to put on em to inhibit corrosion on down the line.

The question behind the bypass answer is why. Why did they get so hot?
I've put NachoRT's diagrams together on this page.
Those should help you figure out if they got hot because of a poor connection, a dead battery or other one time high draw, or if this (high current) will be the norm for your car.
There's also links there to a couple of different wiring solutions. You can decide which one is most appropriate for your set up.

I like soldering. That said, it has drawbacks and the terminal connections can be made better with good crimps. The terminals are mostly 'packard 56' sometimes called 'delphi 56' open barrel connectors. These can be purchases new if needed. Just be sure to get the correct size for the wire gage.

Thanks for the responses and diagrams. Someone else has been into this before me so not sure why this happened. What exactly is MAD upgrade ? Considering the age of the wiring I'm considering a new harness to be safe and an alternate volt meter to bypass the ammeter, Thanks

The MAD approach is to 'bypass' the ammeter.
NachRT74 strategies are approaches to keep the ammeter.

There's lots of reasons why these get hot and even melt. Knowing exactly which ones got hot will help pin down the why.
The Wire from the Alternator Bat terminal goes through the bulkhead connector to the main splice. Everything comes off that main splice.
Is that the only connection that got hot?
It just might have been dirty or corroded terminal at the bulkhead.
It could be a circuit grounding out (chafed insulation) before the fuse box or circuit breaker.
Or is it the Battery wire to bulkhead that got hot?
What was the ammeter showing? That can tell a lot about what and where something is going wrong.

Connections at the back of the ammeter along with the bulkhead connector are known weak spots in the system... since day 2.

If it is a resto and/or you really want to keep it "stock" then 1) make sure electrical loads are not exceeding OE. No big stereos, alternators or other accessories. 2) replace failed wires and connectors 3) scrub remaining connectors clean with emory or replace every connector. 4) grease every connector and re-assemble 5) enjoy.

Otherwise, bypass the whole (weak) affair. A 10 gauge or heavier wire between the alternator post and batt+ or fender relay will take the heavy current off the bulkhead connector and ammeter. You will need a voltmeter on a switched ignition circuit to monitor charge system condition. I had my factory ammeter converted to volt meter. No visual difference. The bypass wire should have a fusible link sized 2 gauge sizes less than the main wire... or fuse sized at alternator output +25% (minimum).

I took the bypass approach.

#1 decide if you are willing to give up your ammeter function. If so then the Madd bypass is good. If not (my pref) then do Nachos' bulkhead parallel bypass in addition to cleaning every terminal/connection including ground paths. I'm thinking you just had a bad terminal connection at the ammeter & if you correct that then you should be good (I would do the bypass) as the bulkhead is a problem area & relaying any add ons to the alt is a good plan. #1 keep the ammeter needle close to 12 0'clock & do not use the alt to charge up a depleted battery.

Here is the diagram for your car. Always start with the right diagrams because they have the location, color and size of the wires to help in your repairs.

http://www.mymopar.com/downloads/1968/68BelvedereGTXSatelliteRoadRunneFull.pdf

Now for your questions.

I have bypassed the factory ammeter wires on a few occasions like you asked. Like Rapidrobert said it's better as a proactive approach. THE REAL PROBLEM WITH ADDING WIRES is in the junction in the main underdash harness. You can run a larger wire from the alternator to the back of the ammeter and then another wire from the ammeter to the fusible link, then battery. Preferably with a better connection than the bulkhead had from the factory.

That will augment the harness and reduce the load on the factory wires but there is a junction inside the harness that feeds the major circuits. You must connect the extra wires and the factory wires to the back of the ammeter. If not it you will not have power to any of the cars circuits including the car's ignition switch, headlights, fuse block etc. If the wiring is damaged and you don't get a good connection to the junction in the harness your car won't work either. If you are seeing burnt wires then I suggest repairing/replacing the harness to be sure of no hidden gremlins under the dash.

If the harness is damaged I suggest pulling it and rewiring it. You are gonna have to pull it to replace it, so if it doesn't look like you want to repair it after you get it out then at least you are halfway through the replacement job anyway. It's a day to two day job and not hard just time consuming because you want to check every wire in the harness just to be safe. It's a little easier in the newer cars where the entire dash frame can be pulled out completely. Some older cars can't be removed but I have rewired Challengers without pulling the dash. It wasn't as easy but it was doable.

As for why the Ammeter wires overheated.
1. All the current runs through the ammeter to get to the battery.
2. Old age corrodes connections and causes them to heat up. The ammeter being a high current connection it heats up more.
3. There is no current flow protection on the alternator side of the wiring so when you have a dead battery the alternator pumps out mega juice to fill it. Also if the voltage regulator/alternator malfunctions it can cause an overcharge problem. With old/bad connections only part of the current flows to the battery and the rest is lost in heat making the problem worse.
4. Eventually the heat takes it's toll on the fiber insulators under the ammeter and they degrade causing a dangerous potential for fire.

Imagine if you will an ammeter shorts from failed insulators while the car is running. First it pops the fusible link but with no overload protection on the alternator the car will still run pumping out juice into the shorted ammeter and poof.

If you repair the harness or buy a new one, put a fusible link on the alternator output. Cheap insurance in case of a short or bad voltage regulator that causes a runaway alternator problem. Also up-size the wires to the ammeter if you repair it yourself or augment the wires in the new harness for extra protection.

Also friends never let friends use crimp connectors only. Always solder, even if you crimp first.


Hope it helps.

thanks for the responses, looks like I'm going to be replacing the harness and going with a volt meter. Can the harness be replaced by pulling the cluster and steering column ? ,I would rather not pull the dashboard as it's a restored original Hemi car. Thanks

being a "restored" ( sorry the " " but it seems not quite complete restore... electrical must be part of the restoration and is very commont overlook this area, hence the fails after 40 years... they get worn like a camshaft, but nobody takes seriouslly the electricity like the mechanic parts, then is car's fault ) Hemi, why don't get the electricty RESTORATION seriouslly on the Hemi car like the rest of the parts already restored ?

IT IS POSIBLE! just need to understan how electricity works, like you know how the carbs goes

Yes it can be done but it is a little more work.

Pull the cluster, lower or remove the steering column and the two kick panels. Peel back the carpet around the high beam switch in the floor and it is usually easier if you remove the glove box on many cars.

That should give you access to all the wiring connectors. Just peel and replace.

I am not a fan of Voltmeters. A voltmeter is rarely accurate enough to let you know there is a problem until the problem is progressed enough the car may not start or run. An ammeter is an immediate indication of a problem.

More importantly an voltmeter will not eliminate the shortcomings of the harness just the ammeter insulators that are the most common problem. You still need to address the weak connections at the bulkhead and ignition switch.

I still suggest you take the old one out and give it a shot at rewiring yourself. Even if you replace it it is a good skill to know.

#1 reason for frying the wires leading to the ammeter is the connections at the firewall bulkhead from the alternator and/or the battery not being weather tight and corroding over time. Corrosion = resistance = heat. Keep those clean and greased, and the connections tight at the ammeter and you should not have a problem. That circuit supplies juice to the whole car, except for the starter motor main circuit - either from the battery when the motor isn't running, or the alternator back to the battery when it is. The factory even bypassed the harness connection for that circuit on some fleet models and made direct connections for it, so it's a known issue.

Even that is a reason, is not necesarilly the number 1 or the only one. Those wires/terminals at bulkhead overheat even being new since packard terminals are not able to handle the load going through when alt provides max output at increased rpms once the batt got drained while engine is iddling. If you correct the power capacity coming from alt side at idle you are 70-75% safer than with the stock capacity alt even with the stock wires and terminals

Which gets back to the question of WHY this particular damage occured. Popular perception on most likely problem is useful when normal diagnoses is exhausted. In the other current thread on same topic (title "fusible link") the problem ended up being that that the alternator failed. So, all the power was being supplied by the battery. Knowing the specifics people were able to help the owner troubleshoot and find the root problems.


Once we know which wire(s) or connections got hot enough to melt, it will be possible to narrow the reasons as to "why this happened".
Even though the wires may have been repaired, altered or modified, it should be possible to figure out what happened.