Need help diagnosing '77 electrical trouble

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merrill77
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Need help diagnosing '77 electrical trouble

Post by merrill77 » Sat Apr 21, 2018 12:19 pm

2 weeks ago, pulling out of the gas station, smoke starts pouring out from the dashboard - roughly under the steering wheel and/or glovebox. Pulled over and turned off the ignition. Smoke subsided quickly. After poking around a bit I turned the key to find everything dead. After towing home, a voltmeter on the battery says 13v, so all good there.

A little research led me to believe an ammeter failure to today I set out to bypass in the engine bay (http://www.ifsja.org/forums/vb/showthread.php?t=105253). I picked up the new parts and started identifying the components involved. Since my '77 is not stock (EFI) I also consulted the 77 wiring diagrams and started trying to match up the diagram with my wagon before I start rewiring.

After reading the diagrams, I feel I must be misunderstanding something...likely a few things.

1) Why is my car dead? The ammeter is between the alternator and the rest of the system. Its failure will prevent charging...but shouldn't disable the rest of the electrical system (if the battery is charged). This is what I grok in the wiring diagram, but seems to disagree with reality. What disconnects the battery from the rest of the system?

2) AFAICT, completing the ammeter bypass will not get my wagon running because it doesn't fix whatever else is broken. Correct or not?

3) Is it correct that the voltage regulator is separate from alternator in this car? Is it a 3" square black box on the fender next to the battery and starter solenoid?

4) Why did somebody think that combining the 6cyl and 8cyl diagrams into one was a less-than-horrible idea?

TIA!
Chris
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Re: Need help diagnosing '77 electrical trouble

Post by SJTD » Sat Apr 21, 2018 12:51 pm

If it was letting smoke out I think you need to pull the cluster out and see what's burned.

Turning off the key probably didn't do anything to stop the burning. Whatever shorted out burned out on its own.
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Re: Need help diagnosing '77 electrical trouble

Post by ghcoe » Sat Apr 21, 2018 1:38 pm

Here is a article that may be some help to you http://www.madelectrical.com/electrical ... uges.shtml .

1. If you look at diagram #1 in the article you will see that there is a splice in the system that supplies power to the ignition, fuse box and light switch. If you notice this splice is on the alternator side of the amp meter. That would probably be why you have no power to the rest of the vehicle.

2. If you notice in the article there is a page 2 link (at the bottom). This will show you how to do a bypass and improve on the charging system at the same time.

3. They figured a person with electrical knowledge would be looking at the diagrams instead of a newbe.....!

If you got lucky and the amp meter is all that failed this article should get you back on the road. There is a lot of extra info in the article that goes into the fire wall plug as well. If the plugs are still good ignore those parts. Good luck, George.
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Re: Need help diagnosing '77 electrical trouble

Post by ghcoe » Sat Apr 21, 2018 1:38 pm

Double post
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Re: Need help diagnosing '77 electrical trouble

Post by tgreese » Sat Apr 21, 2018 2:05 pm

The charging wire goes to the dash, through the ammeter and back to the battery. If you disconnect the ammeter (not bypass) you shut off power to the dash and rest of the car.

I made this sketch -

Image

This is how I bypassed my '82. The '77 is the same. Yes, a '77 with a V8 has a separate regulator. This is shown in both the wiring diagram and described in the '77 TSM.

The only difference between the 6 and V8 is the type of alternator. Apparently this was not a sufficient difference to need a separate diagram. The TSM is written for professional mechanics working at the dealership. If you have trouble understanding it, ask.

The 14 ga wire is a fusible link, shown on the wiring diagram. You may have blown the fusible link in the wiring. Test continuity between the starter solenoid and the ammeter.

Above is before, below is after. "Bulkhead" is the big bulkhead plug on the firewall.

There is a sticky thread with many threads about this on IFSJA. http://www.ifsja.org/forums/vb/showthread.php?t=184890
Last edited by tgreese on Sat Apr 21, 2018 2:30 pm, edited 1 time in total.
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Re: Need help diagnosing '77 electrical trouble

Post by tgreese » Sat Apr 21, 2018 2:29 pm

Duplicate post.
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Re: Need help diagnosing '77 electrical trouble

Post by merrill77 » Sat Apr 21, 2018 2:36 pm

ghcoe wrote:Here is a article that may be some help to you http://www.madelectrical.com/electrical ... uges.shtml .
Thanks, that article does help a bit.
tgreese wrote:I made this sketch
That helps, too. Thanks!

I spent some more time studying the '77 electrical diagram and I'm now understanding a little better. When the engine is off, the alternator is essentially an open circuit. Which makes the Yellow wire from the starter solenoid function as power delivery from the battery to the ammeter and then to the red wire which splits to deliver power to lights, ignition switch, etc. When the engine starts, then the alternator (Red wire) is supplying power and current flow through the ammeter reverses. I think I get it now - I usually think of systems where power always flows in the same direction. But in this case, it flows backwards when the engine is off and this is indicated by the negative side of the scale on the ammeter.

Assuming the ammeter failure results in an open circuit, its failure will result in no lights, ignition switch, etc. when the alternator is not running because power has to flow through the ammeter it to get to the splice that distributes to other systems in the dash.

So even with the ammeter bypass in the engine bay, I still need to wire together the two terminals at the ammeter. *OR* connect the red wire that originally went to the alternator to the solenoid terminal along with the yellow...replacing the function of the yellow wire and making it obsolete (but potentially useful as another power tap in the dash if needed, after adding an appropriate fuse and/or distribution box).

Back to the garage :D
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Re: Need help diagnosing '77 electrical trouble

Post by tgreese » Sat Apr 21, 2018 2:41 pm

I found it easiest (and tidiest) to splice the ammeter wires together, and reroute the red wire from the ammeter to the starter solenoid. You can remove the brass terminal from the bulkhead connection by pushing back the connector's locking tab using a small sharp instrument like a jeweler's screwdriver.

I put an additional fusible link between the alternator wire and the starter solenoid. The fusible links are meant to protect against the battery connecting to ground in the event of a catastrophe like a wreck.
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Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
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Re: Need help diagnosing '77 electrical trouble

Post by ghcoe » Sat Apr 21, 2018 3:15 pm

merrill77 wrote:So even with the ammeter bypass in the engine bay, I still need to wire together the two terminals at the ammeter. *OR* connect the red wire that originally went to the alternator to the solenoid terminal along with the yellow...replacing the function of the yellow wire and making it obsolete (but potentially useful as another power tap in the dash if needed, after adding an appropriate fuse and/or distribution box).

Back to the garage :D
Yes, you are basically converting the wire to flow current one way instead of two ways. It is a simple conversion.

There is some info here near the bottom of the page http://www.fsjnetwork.com/forum/viewtop ... =12&t=4332 on how to convert the amp meter to a volt meter so you can still monitor the battery.
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Re: Need help diagnosing '77 electrical trouble

Post by merrill77 » Sat Apr 21, 2018 6:21 pm

Thanks...I've seen references to that post, but had not found it yet. I have bookmarked it, in case I decide to go that direction...I am considering a complete cluster replacement. For now, I will add a voltmeter under the dash.
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Done with bypass

Post by merrill77 » Sat Apr 21, 2018 6:31 pm

I finished the ammeter bypass in the engine bay (per the link in my original post) and re-routed the red wire to the solenoid. As expected, the latter restored power to everything else. I didn't fire it up yet...it was getting late and I will need to be alert, as Ryan and I also re-installed the heater box with new heater core today. Still need to check it for leaks & top off the coolant.

Now...if I can just figure out why the courtesy lights suddenly won't go out :(
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Running well :)

Post by merrill77 » Sun Apr 22, 2018 2:15 pm

Wired in a voltmeter, temporarily, in the glovebox to a switched source. Voltage was right at 12V and, as expected, drops to 7-8 when cranking, then sits near 14V when driving, maybe a little under. So it seems the charging system re-design was successful. Thanks to araknid75 over on IFSJA and to all of you here! It took me a lot longer than the 40 minutes he said it took him. I took extra time to solder all the crimped connections...but even without that, it probably took me a good deal longer.

Thanks again!
Chris
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Re: Need help diagnosing '77 electrical trouble

Post by fulsizjeep » Sun Apr 22, 2018 3:51 pm

Did you happen to find the lug connections on the ammeter were not tight? I have my own theories around this fire hazard. I have parted a few FSJs with this design and 3 of them had ammeters that were toasty. The lugs on all of them were not tight. Bad connections like this can create extra current through the circuit than planned and well, they get toasty as a weak link.

Good to see it is running right. :-bd
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Re: Need help diagnosing '77 electrical trouble

Post by merrill77 » Mon Apr 23, 2018 5:10 am

I actually have not yet touched the ammeter. After the re-wiring, it should have the same voltage on both terminals, so I'm not concerned with the ammeter as a hazard.
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Re: Need help diagnosing '77 electrical trouble

Post by will e » Mon Apr 23, 2018 6:46 am

So can I just add the fusible link between the alternator and battery and leave the amp meter wiring place?
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Re: Need help diagnosing '77 electrical trouble

Post by merrill77 » Mon Apr 23, 2018 7:37 am

That is what I did. I used a circuit breaker, though, as shown in the post I followed. Easier to reset a breaker on the side of the road :) If I remember it is there.
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Re: Need help diagnosing '77 electrical trouble

Post by tgreese » Mon Apr 23, 2018 9:26 am

will e wrote:So can I just add the fusible link between the alternator and battery and leave the amp meter wiring place?
If you run the red alternator wire directly to the battery, you should bypass the ammeter. This could be putting both wires on the same post, but I cut the wires and spliced them together with a butt connector and soldered joint. If you remove the bulkhead plug from the engine compartment side, you can remove the red 10 ga wire and use that to run to the solenoid. My sketch above does not show it, but I abandoned-in-place the red under-dash 10 ga wire from the bulkhead connector to splice B.

I also added a fusible link between the alternator and the battery. This protects the car from fire if the alternator is grounded in a wreck or such. Jeep uses that scheme in the '75-up CJ, which has a dash voltmeter in place of the ammeter used through '74. Personally I think putting a circuit breaker there does not really add anything to the circuit other than complexity and an additional part that could fail. The fusible links serves to isolate the battery from ground in the event of a catastrophe... making it easy to reset is kind of pointless.

Image

This is from the '76 CJ diagram showing the Delco distributor. If you are interested in how the Motocraft alternator and regulator are connected, it's shown here http://oljeep.com/gw/76_tsm/Section22.pdf
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green
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