1974 Monaco Charging Issue

[Chicago Bluesmobile]

My 1974 Monaco is not getting a charge from the alternator to the battery.

When I got the car alternator was extremely corroded, and the belts were worn and loose.

I replaced the alternator with a 95amp Powermaster with the internal regulator. Tightened everything down. Made sure it was grounded. Same result.

I’m getting 14.5 volts at the charge wire and where it branches off for the factory battery isolator. I’ve cleaned all of the grounds, and they test good.

The negative battery cable was in really bad shape, cracking and peeling, so I replaced that and the positive cable for good measure since the eyelet end had some major cracks in it.

Cleaned the battery terminals, connected everything and was still not getting a charge to the battery. 12.6v at the battery and no movement when revving the engine. I had the battery on a trickle charger and it was fully charged when I started testing, but would slowly creep down.

The $70 Wal-Mart battery the previous owner put in last summer was completely drained several times, fearing a dead cell and not feeling it was worth load testing it I bought a new higher quality battery and same results.

The original ammeter barely moved, and showed no discharge, I replaced it with one I had and now is definitely showing a discharge, but no charge whatsoever.

I’m at a total loss at this point and have come near the end of my troubleshooting skills.

Any ideas what I should check next? Thanks in advance.

 

[CBODY67]

"Factory battery isolator"?

 

[Chicago Bluesmobile]

"Factory battery isolator"?

Car is a factory tow package and the isolator charges the car and trailer batteries. But since there’s not trailer or additional batteries I wouldn’t think that is the issue.

 

[1970FuryConv]

Hi Brian
Sound like you have a bad connector somewhere.
I would use my voltmeter and working downstream from the alternator output wire, check every connection until I found one where voltage drops from 14.5 to 0.
Best of luck, Ben

 

[Vaanth]

My 1974 Monaco is not getting a charge from the alternator to the battery.

When I got the car alternator was extremely corroded, and the belts were worn and loose.

I replaced the alternator with a 95amp Powermaster with the internal regulator. Tightened everything down. Made sure it was grounded. Same result.

I’m getting 14.5 volts at the charge wire and where it branches off for the factory battery isolator. I’ve cleaned all of the grounds, and they test good.

The negative battery cable was in really bad shape, cracking and peeling, so I replaced that and the positive cable for good measure since the eyelet end had some major cracks in it.

Cleaned the battery terminals, connected everything and was still not getting a charge to the battery. 12.6v at the battery and no movement when revving the engine. I had the battery on a trickle charger and it was fully charged when I started testing, but would slowly creep down.

The $70 Wal-Mart battery the previous owner put in last summer was completely drained several times, fearing a dead cell and not feeling it was worth load testing it I bought a new higher quality battery and same results.

The original ammeter barely moved, and showed no discharge, I replaced it with one I had and now is definitely showing a discharge, but no charge whatsoever.

I’m at a total loss at this point and have come near the end of my troubleshooting skills.

Any ideas what I should check next? Thanks in advance.

As noted, and after the checks and cleaning you have already done, tracing through the charging path(s) to look for voltage drops or incorrect voltage changes is in order.

Regarding the isolator, when working correctly, it will introduce a ~0.7 volt drop in each charging path direction due to the drop across the internal diodes. So, any marginal changing can be compounded by this even in a properly working isolator. If it has developed external, or internal high resistance points in the main battery charge side, these will add to the drop in that side. If the diode in the main battery charging path has opened, charge flow between the alternator and battery, will not occur. If the diode has shorted, it should reduce the voltage drop initially, but the shorted diode junction could overheat compounding any drop. This car does not pass full charging current through the ammeter in the instrument cluster, but rather shunts a small portion of the charging current through the bulkhead for the ammeter.

If you are not using the trailer tow side, the isolator can be bypassed in a couple of ways. The center connection is directly from the alternator. One side connection goes to the rear trailer tow wiring for an auxiliary battery and the other side runs to the main battery positive lead with some branches for bulkhead feeds.

To bypass the isolator, do the following:
1. Disconnect the battery.
2. Determine which isolator side terminal is connected to the wiring that charges the main battery.
3. Disconnect this side terminal determined in step 2.
4. Unwrap this wire from the harness until it can reach the alternator charging stud.
5. Remove the wire from the alternator charging stud, which is connected to the isolator center terminal and secure away from the alternator.
6. Connect the previously disconnected and unwrapped main battery charging wire, determined in step 2, to the alternator charging stud.
7. Reconnect the battery.
8. Start the engine and check for charging operation.

As an alternative, but less desirable one, do the following:
1. Disconnect the battery.
2. Determine which isolator side terminal is connected to the wiring that charges the main battery.
3. Disconnect this side terminal determined in step 2.
4. Disconnect the wire from the center terminal of the isolator.
5. Connect the removed side terminal wire, determined in step 2, and the removed isolator center terminal wire together securely.
6. Insulate the connected wires with tape or other material.
7. Reconnect the battery.
8. Start the engine and check for charging operation.

The second method is quicker, and could be used as a temporary connection to test for operation. The first method should be used for a more definite and permanent connection.

 

[CBODY67]

Car is a factory tow package and the isolator charges the car and trailer batteries. But since there’s not trailer or additional batteries I wouldn’t think that is the issue.

View attachment 728228

THANKS for that additional information! I don't recall ever seeing any mention of a battery isolator in the sales literature as a component of the HD Trailer Tow Package. Which is why your mention of it, initially, did not register. BTAIM

GM used battery isolators on some 1990s pickup trucks with a factory tow package, which would keep the additional 12V battery (used the same battery mounting and cables as the dual-battery configuration on the diesel pickups of the time), but they never caused any problems.

I concur with @Vaanth that you need to fully isolate that part out of the charging system in order to do a full diag on the issue. The shunted charge path to the ammeter started in the 1972 model year, so the ammeter needle moves little when the alternator is charging, unlike prior model years when all of the current went through the gauge.

Please keep us posted on your progress,
CBODY67

 

[Vaanth]

Following is the wiring diagram areas for the isolator wiring from the 1974 factory service manual:

I forgot the terminal block in the circuit that is another point to consider if bypassing or just when tracing the wiring for connection issues.

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My 1974 Dodge D200 Club Cab truck was built with the camper chassis. The camper chassis included an isolator, two batteries, and a 65 amp alternator. The main battery is in the standard location and the auxiliary battery was in the front passenger side corner of the engine compartment. When I got it in 1990, it still had the original 1974 Mopar battery in the auxilliary location that was corroding the area. he factory isolator was connected, but the auxiliary side was open, possibly from trying the charge the long dead battery.

I replaced the isolator with a new unit -- a nice USA built, relatively inexpensive unit from JC Whitney -- and I rewired the system to run a Chrysler 100 amp alternator, the same as those on my police package cars. This entailed changing all the bracketing too. The system worked well. I did not use it for the camper chassis wiring, but I wired a setup to power a trailer winch. Eventually, I removed the isolator and second battery, but kept the alternator setup. I no longer needed it and needed the space to add a Little Red Express Truck ram air setup.

It did come in handy once when, my main battery died while out somewhere. I got out my jumper cables, connected the main battery to the auxiliary battery, and jumped myself to start the truck.

 

[Chicago Bluesmobile]

Thanks for the advice! I will keep you updated with what I find!

 

[Chicago Bluesmobile]

@Vaanth your advice was spot on! The isolator has an open loop on the main battery side. I’m not towing with her so I opted for Option 1 and she’s charging beautifully now! So excited that I’ll be able to take her out for a cruise!

I don’t mind that I replaced the alternator, cables, and battery as they all looked suspect. But I know that the isolator was the problem all along. It’s a learning experience.

Maybe someday I’ll put the isolator back in play for a factory appearance.