Blue Field Wire Meltdown?

[Shrimpy]

Howdy from Texas and I am glad to join the mopar community!

I recently acquired a 1974 Plymouth Valiant. It is a great car and drove great until it developed a charging issue. I replaced the alternator and battery as they had tested bad and hooked up the connections correctly. There is no issues when key is not on the run position but when key is turned, the blue field wire melted from the alternator down to the firewall. (not quite the bulkhead connector however)

It should be noted the path to the voltage regulator is unharmed.

Where do I start from here?


Some key points, connecting a multimeter to the terminal and positive battery reads 12v as does the bulkhead connection reads 12v even when terminal is disconnected.

 

[dadsbee]

The alternator you bought has the field wire spade grounded out to the case when it should be insulated. Remove Blue and Green wires. Using your meter on OHMS check from each spade to case and I bet you find one (or both) of the spades are grounded to case when they both should be insulated from same.

 

[Shrimpy]

I noticed a similar thread where the member had improper connections but it seems that my connections are insulated.

 

[Tooljunkie]

Ohmmeter test. Only way to know for sure. Or take it apart.

 

[Shrimpy]

It reads around 3.9 between the 2 spades, 4.1 from green spade to the case, and 7.1 for the blue spade to the case. The numbers fluctuate greatly but that is the pictures of the most stable reading.

 

[Mattax]

It reads around 3.9 between the 2 spades, 4.1 from green spade to the case, and 7.1 for the blue spade to the case. The numbers fluctuate greatly but that is the pictures of the most stable reading.

There's the problem. Neither field terminal should have any connection to ground.

The point of an isolated field alternator is the regulator controls the connection to ground.
Identifying Chrysler Alternators (1960-1976)

 

[Shrimpy]

There's the problem. Neither field terminal should have any connection to ground.

The point of an isolated field alternator is the regulator controls the connection to ground.
Identifying Chrysler Alternators (1960-1976)

Would that be an internal issue with the alternator? It seems like an alternator replacement is in order then?

 

[Tooljunkie]

Would that be an internal issue with the alternator? It seems like an alternator replacement is in order then?

Yes. Take your meter and test the new one. Saves some hassle.

 

[67Dart273]

Would that be an internal issue with the alternator? It seems like an alternator replacement is in order then?

This may be a shorted rotor BUT IT IS ALMOST ALWAYS an issue with the brushes/ brush holders/ brush holder insulators. Take a GOOD look at the brush holders. Both should have shoulder washers to insulate the brush terminal. If you take your time take them apart one at a time, and re--check continuity to the case with one brush removed you can find the culprit. Most of us can tell just by looking

Back in the day, we would NEVER replace a nearly new alternator just because of a brush. You can still buy brushes if you can find them.

 

[Shrimpy]

Yes. Take your meter and test the new one. Saves some hassle.

They put me up with a free upgrade, guy said he could not even get it properly hooked up to the tester. New alternator tests great let’s see.

This may be a shorted rotor BUT IT IS ALMOST ALWAYS an issue with the brushes/ brush holders/ brush holder insulators. Take a GOOD look at the brush holders. Both should have shoulder washers to insulate the brush terminal. If you take your time take them apart one at a time, and re--check continuity to the case with one brush removed you can find the culprit. Most of us can tell just by looking

Back in the day, we would NEVER replace a nearly new alternator just because of a brush. You can still buy brushes if you can find them.

I hear you, kits are not up for these alternators while whole alternators are cheap and on the shelf. Let’s see!

 

[Dana67Dart]

the blue field wire melted from the alternator down to the firewall

Unless you can see the blue wire from one end to the other I would suspect that some other wires insulation is also melted.

 

[dadsbee]

Look like steel washers to me, under those spade retainer bolt heads. I can't believe the number of re-manufactured alternators being sold this way. You're #4 I know about in the past month..

 

[Mattax]

All the small parts are cheap.
Even with shipping.

Alternator repair, a little show and tell.

Replacing the wire is going to cost time.
Don't cheap out on the wire or the crimps.
On a '74 it probably has branches to the choke assist and maybe some other carb related devices. So it will need inline splices.

Inline wiring splice clips........from the Dodge RAM service manual