Something electrical But what?

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J

jblueridge

SILVER Star
10 Year
Joined
Aug 12, 2014
Threads
275
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3,361
Location
Near Charlottesville, VA
I also posted this in the 24V Diesel area
Yesterday I was watching a student fly his RC electric plane. He plugged his battery charger into my re-wired-for-12V cig lighter. The 12V radio came on. I wondered how either of these devices could be working because I have a 24-12V converter that requires the ignition switch to be on (24V relay, etc.)
About an hour later, I tried to start the beast and got no response. The usual dash lights came on briefly, then off. I drift started it and drove around a bit. Parked it, shut it down, then tried to restart: still nothing.
Just a little while ago, I hooked my charger up to each battery in turn. Running at 15 amps, each battery seemed "full" after about 15-20 minutes. The charger's ammeter started out at 15 and gradually dropped off to nil. I don't think the batteries were dead.
I suspect the 12V wiring is somehow at the root of this but I did not find a single blown fuse. I glanced at the fusible links just off the battery and there is no sign of heat/melting/fire.
I'll put the batteries back in tomorrow but I'll not connect any 12 V stuff.

Any advice?
 
I'm going to put the batts back in tomorrow. I'll not connect anything related to 12V.

When checking out wiring diagrams, I could not find a starter relay in the BJ74.
is that right?
 
Last edited:
I put my charged batteries back in.
I disconnected and de-fused anything related to 12Volts.
I found a noisy/faulty head light relay.

Still get nothing at all when key is turned.
 
I was able to test a bunch of stuff today.

Thanks to Beno and Ozcruiser I found the starter relay behind the forward battery.
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Hooked that relay up to the Power Probe and it responded with clicks.
Checked for open circuits and short-circuits following FSM protocol: all correct.
I guess it is okay.

I unplugged the ignition switch and compared it to the FSM.
I was expecting to use the bottom-most of these 3 pin diagrams.
Instead I found Pin 5 missing.
I could not find Connector B.

I tested the connector as if Pin 5 = Pin 4. It all checked out okay.

So I have not yet found the fault.

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upload_2017-4-1_14-49-23.webp
 
Yes, I checked the three right off the battery. I should have mentioned that. They have good continuity. I guess something funky might be happening when the full current is flowing through.
Tomorrow, I might try a temporary bypass of them to see what happens. Just put some plain old wire in there as a test.
 
I would also check the nylon washers on the glow system it stops the 12/24 volt system from grounding on the manifold. Not sure what engine you have but if you have a glow system it's worth checking. They join two buzz bars together on my old 2h with a white and blue nylon type washers.
 
Its the Glow screen. Air is heated at intake manifold.
Tomorrow I'll check possible short circuit there.

Thanks.
 
I re-charged my batteries again with an old-school charger. The dial showing amperage quickly fell off, indicating a full charge.
I borrowed a jump start battery pack that purports to show the % battery charge. This device showed the batteries are only maybe 34% charged after I charged them.
Voltmeter shows 12.8 and 13 Volts respectively.
Hard to believe the batteries aren't charged but I will have to get measurements while they are under load.

Funky jump start battery pack.

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Load tested the batteries and they both stayed within the Good range.
I hope to fnd something faulty sometime.
 
If you haven't done it already pull the 24/12 converter from the truck and go back to the stock wiring system something with the converter or install is causing you the headache.
 
Thanks Oz, but I did that first thing. The whole 12V system is disabled. Converter,and everything further along, disconnected. 12 V radio removed.
 
I pulled the starter out just to check it. Seems okay.
I am going to get new battery cables.
I am cleaning up the few ground points I can find.
 
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