Blowing fuse on an April 1978 FJ40 (1 Viewer)

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Hey team,
I've made some good progress with my build but now running into a small issue. I am blowing the fusible link POS BATT side but ONLY when the circular instrument cluster plug is connected. I am working my way through the schematics for this year but thought id ask the group for a little insight if possible. The ammeter is connected and all else is as well. The rig will turn over with cluster disconnected but if I then disconnect POS terminal, plug in the instrument cluster and reconnect the POS terminal, the fuse between the ammeter and POS terminal blows.
Appreciate any ideas.
Cheers,
Steve
 
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Hmm, I just grabbed a fusible link from Orielly and dropped a 20a fuse in. Your saying there is a special fuse and link I need? If so I’ll need to reach out to @Coolerman.
Thanks!
 

samatulich

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I used a fusible link from the auto store and would blow a 15 or 20amp fuse(AFAIK) occasionally. Since I replaced it with one from @Coolerman, I have not had a problem. I could be wrong, but it is my understanding that the fusible link he makes guards against heat better, where as the standard 20amp fuse would just blow. Like I said, maybe I’m mistaken.
 
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I used a fusible link from the auto store and would blow a 15 or 20amp fuse(AFAIK) occasionally. Since I replaced it with one from @Coolerman, I have not had a problem. I could be wrong, but it is my understanding that the fusible link he makes guards against heat better, where as the standard 20amp fuse would just blow. Like I said, maybe I’m mistaken.
Thanks! Would love to learn more. Will reach out.
Cheers!
 
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What is the 1978, early or late ? Also , that fusible link is tied to the alternator. Have you looked at that ?
 
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ok, found that if I disconnect the instrument cluster it's fine but connected it blows the fuse. In one case it even fried some of the ribbon traces on the instrument panel. I fixed those with small copper wire soldered back but now need to figure out why the fuse blows only when the cluster is connected.
Appreciate any ideas!
 

hobbes

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Might not help, but until someone smarter comes along here I‘d pull all my fuses and see if that changed anything.

Also does it blow immediately, when you turn the key on, or just when you try to start it?

All the current flows through the ammeter so you certainly don’t want to damage that. If it’s blowing with the key off, I’d start looking at the “always hot” circuits.
 
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Thank Hobbs, yeah, it's an always hot circuit somewhere. Blows with all fuses out. If I have the instrument cluster plugged in it blows the fusible link immediately. If i disconnect the cluster =, have all fuses out and JUST the ammeter connected it's fine. Engine will turn over. As soon as I connect the cluster, regardless of ignition switch position, it blows the fusible link. I am planning to work through the system with my meter but not sure where to even start. I'll be looking for a ground somewhere.
Appreciate the guidance!
 

hobbes

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Someone posted this here. I saved it for troubleshooting. Might help.

1605390180326.jpeg
 
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colorado
Hey team,
I've made some good progress with my build but now running into a small issue. I am blowing the fusible link POS BATT side but ONLY when the circular instrument cluster plug is connected. I am working my way through the schematics for this year but thought id ask the group for a little insight if possible. The ammeter is connected and all else is as well. The rig will turn over with cluster disconnected but if I then disconnect POS terminal, plug in the instrument cluster and reconnect the POS terminal, the fuse between the ammeter and POS terminal blows.
Appreciate any ideas.
Cheers,
Steve
 
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Dec 14, 2005
Messages
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Location
colorado
This is two hours of free advice otherwise would be available in a shop. You'll save a lot of time doing this. You need to go out and buy a digital multimeter how that has the current measurement option. Go and take the multimeter switch it to 10 amps. Place one probe on the positive cable secure to the cable. And take the other probe and put it to the positive by the battery. If the probe leads are long enough take the meter and placed against the windshield. You will see the current draw on the meter. Start pulling fuses and put them back in their spot. I would start with the largest fuse and then work your way down. What's the current drops to 200 milliamp years or less you just found your current draw. Another option I never thought of it's just use a light bulb even a headlight. I put the headlight in series between the positive wire and the positive cable and both fuses and the light will dim or go out. Never thought of that before but is probably a very cheap way of finding excessive current draw.
 

middlecalf

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Not sure about a ’78 but earlier cluster gauges are protected by a 5A fuse, so that would have blown if it’s an issue with the cluster well before the 20A harness fuse would have blown.
 
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If replacing the fusible link with a fuse, 30 amps.
But, unless you have the lights on, fan on, wipers going and honking the horn while trying to start it, that's not the issue. And you're probably better off sticking with 10 amp fuses until this is resolved.
Something is shorting, and because it's blowing the fuse on the battery, especially if you have a 20 amp fuse on the battery, and not the fuse on the pannel, I'd be very suspicious of the amp meter. Although, you are using 20 amp fuses on the battery and the fuse for gauges is also 20 amps.
1605392597962.png


Pull that fuse from the panel, get your multimeter and test for ohms between that fuse connector on the panel and ground. It should be high.

With that fuse out, reconnect everything. If it's still blowing your fuse, probably the amp meter.

You can take the wires off each side of the amp meter, screw the two connectors together and wrap them with tape if you want to make totally sure it's not an issue. (and do make sure they are well very wrapped with tape)

If not... And from that spot on the fuse panel to ground has very low resistance, I'd start pulling all the light bulbs, pulling (and taping up) the connectors on the oil pressure, temperature and gas gauge sending units, and trying again.

The turn signal and high beam indicator are also connected there, but without having lights turned on I don't think there's going to be current on that circuit that would blow a fuse.
 
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Great feedback gang! I'll take all this advice and start working through it and let you know what I find.
Cheers!
-Steve
 
Last edited:
Joined
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Yep, took instrument panel
Apart and found a post for the ameter missing an insulator and touching the casing. Looks like problem found. Thanks for your help team!
If I have any more issues I’ll reach out.
Cheers!
 

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