Strange Electrical Issue at Fuse Block

Joined
Feb 14, 2013
Messages
838
Location
Wake Forest, NC
Hi All -

I recently finished a bunch of mechanical work on my FJ40 1970 ('71 wiring diagram). I must have messed something up because now, when I go to start the vehicle, I constantly get a 20 amp fuse burning out. It is the fuse that goes to the yellow (oil press. ga, temp ga, and fuel gauge) and red-blue lines (back-up light/switch).

Reading past threads on the forum, I removed the fuse, attached an amp meter on the fuse block, and turned on the ignition switch. I got zero amps. I removed all the components on the lines, turned on the ignition switch, and still got zero amps. Thinking my meter was broken, I check the voltage across that fuse and got the normal 12 volts. I then put another fuse in, and it burned out right away.

Any thoughts as to what is going on? I figured with no amps, the fuse would not burn out. However, it continues to burn out right away.

Thanks for any help

@Coolerman
@Pin_Head
 

Green Bean

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May 9, 2021
Messages
291
Location
78620
Hi All -

I recently finished a bunch of mechanical work on my FJ40 1970 ('71 wiring diagram). I must have messed something up because now, when I go to start the vehicle, I constantly get a 20 amp fuse burning out. It is the fuse that goes to the yellow (oil press. ga, temp ga, and fuel gauge) and red-blue lines (back-up light/switch).

Reading past threads on the forum, I removed the fuse, attached an amp meter on the fuse block, and turned on the ignition switch. I got zero amps. I removed all the components on the lines, turned on the ignition switch, and still got zero amps. Thinking my meter was broken, I check the voltage across that fuse and got the normal 12 volts. I then put another fuse in, and it burned out right away.

Any thoughts as to what is going on? I figured with no amps, the fuse would not burn out. However, it continues to burn out right away.

Thanks for any help

@Coolerman
@Pin_Head
I'm probably wrong on this and someone may correct me, but I was under the impression that the instrument cluster gauges were on a 5 amp fuse

Fuse Block.jpg
 
Joined
Feb 3, 2020
Messages
525
Location
Stanwood, WA
My 2/71, the instruments are on a 5 amp. Either way, I blew mine and it turned out in my excited rush, I didn’t get one of the wires on the post on the alternator and it was arcing. Maybe look there if you were near the alternator lately?
 

73FJ40

After another night of rust removal!
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Dec 28, 2006
Messages
1,674
Location
Western Massachusetts
@stoshzack .

If it is a dead short blowing 20 amp fuses, hooking up a 100 amp ammeter may allow up to 100 amps through your problem circuit. If so, the short will be easily found, located at the end of the melted and charred wire harness. (for reference, the OEM starter draws about 100 amps on a warm day.)

I suggest you check the two circuits leading to the fuel sending unit and the backup light, continuity to ground, with your ohmmeter. Fuel is yellow/ red on the top of the tank, back-up from the light fixture with the transmission in reverse.

After those, the remaining sending units.
 

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