Electical short help

[afd660]

Wondering if anybody can help me out or have any tips. I have an electrical short somewhere. I still have power to the car with the battery cut off switch in the off position. With the switch off I can still turn on headlights, fog lights, fuel pump runs etc etc, but when manually turning on the cooling fan with a switch, a fuse blows. The cooling fan fuse itself does not blow, but the 5 amp EMER SO FUSE does, at least that is what its labeled. Ive also tried the method of disconnecting the positive cable from the battery and attaching a test light to the cable and the probe to the positive battery terminal, light comes on. I've pulled every fuse and relay and the test light still stays on.

Battery cut off switch tests good. All wires disconnected, theres no continuinty with switch off. Switch on theres continuinty. The wires that are connected at the cut off switch are the thicker cable coming from in from the battery and a thicker cable going out to the starter. Theres also a thinner wire that I'm pretty sure leads to the 5amp EMER SO FUSE up in the cabin. Fuse installed continuity and fuse out, no continuity. The battery cut off switch will work when one side of the thinner wire is disconnected from the terminal. Switch on theres power. Switch off, no power. I've tried testing for continuity to ground with the Fluke and there is no continuity from the wire to a ground. On both terminals there is no continuity to ground. Wondering if anybody else has any ideas or something else to test or troubleshoot. Just weird to me that I can turn on all the lights, 4 way flashers and no fuse blows but manually making the cooling fan run it will blow that fuse. It wont blow the EMER SO fuse with the battery switch on and manually turning on the cooling fan, only with the battery switch off. Any help would be appreciated. LOL.

[Mastertech5]

You should be activating the fan relay by grounding one of the extra temp sensor wires through a switch not powering the fan directly if that's what you did. Just a thought.

[michael everson]

Somebody installed a fused wire to keep the computer from relearning every time the battery cutoff was turned off. This was pretty common on FFR builds that had a factory computer. The reason the fan blows that fuse is because it draws a lot of amps to get it started, overloading the small fuse. Sounds like its operating as it should. You have no short.


Mike

[AC Bill]

Yes, as Michael suggests, the builder added a "keep alive" wire for the computer memory. The basic idea was to be able to use the battery master switch as an anti-theft feature. No one could start if they jumped the ignition wires, when the master switch was off.
You could install an even lower amp EMER fuse, as he has labeled it, as the ECM memory only draws about 500 milliamps from what I understand. That way, whenever the master switch is off, almost anything would blow the keep alive fuse.

[afd660]

Oh ok I see what you guys are saying. The previous owner/builder installed a "keep alive wire" to keep the FAST EFI memory and to keep the clock running, even with the battery switch in the off position. I guess I never noticed or tried to run anything before with the battery switch off. So this time when I turned the ignition key and everything powered up, I was surprised.

I would have figured turning on all the headlights, taillights, foglights, radio and stuff at the same time, that would have blown the 5amp fuse. Guess I'm used to the military vehicle cut off switch where it cuts all the power.

If you guys say its normal I'm gonna go with that. I cant figure anything else out or what else to check out. I'll just keep an eye out for smoke or the smell of smoke when running and driving. LOL. Really appreciate it guys. Thanks for your time.

[AC Bill]

I would have figured turning on all the headlights, taillights, foglights, radio and stuff at the same time, that would have blown the 5amp fuse. Guess I'm used to the military vehicle cut off switch where it cuts all the power.

I think that with all those items turned on at the same time, and the fuse hanging in there, all the light bulbs are probably LED. Probably getting pretty darn close to 5 amps draw though, with the fog lights, and fuel pump running. The fan motor draw is demanding far more amps than the fuse can handle. It alone could be 14+ amps on start up.

Wouldn't take any more than pulling the fuse, if you wanted the cut off switch to kill 100% of the power when switched off. The car will start and run, even with the memory wiped clean each time. It just won't run quite as efficiently for the first 15-20 minutes.

[afd660]

I think that with all those items turned on at the same time, and the fuse hanging in there, all the light bulbs are probably LED. Probably getting pretty darn close to 5 amps draw though, with the fog lights, and fuel pump running. The fan motor draw is demanding far more amps than the fuse can handle. It alone could be 14+ amps on start up.

Wouldn't take any more than pulling the fuse, if you wanted the cut off switch to kill 100% of the power when switched off. The car will start and run, even with the memory wiped clean each time. It just won't run quite as efficiently for the first 15-20 minutes.

The lights are all typical halogen, that's kind of why it stumped me as to why it wouldn't blow the fuse. I'm glad you guys told me about the keep alive wire. LOL. I had no idea what that little wire as for. Searching and googling the keep alive had everything make sense. Double checked the wires for any frays or loose connections and everything seems good. So when I get some time and it cools off here down south. I'll button everything back up. Thanks again everyone.