Hello,
All of a sudden my truck (87 pickup, 4WD, 22R engine, 2.4L carb) has developed an electrical short. I don't have a good meter but the drain is at least 0.3A.
I systematically removed each fuse to see whether I can use this to identify the circuit but no such luck. None of the fuses control the electrical short.
I have disconnected power to the starter, alternator and the radio. Short is still there.
I am baffled on where the short is right now. I appreciate any thoughts or suggestions that anyone can provide.
Matt

 

Welcome to YotaTech.
​No excuse for that! https://www.harborfreight.com/electr...ter-63759.html
​​​​​​ 0.3A (300ma) isn't a (real) short. Let's call it "phantom draw." I assume you're measuring from the battery terminal (good). If removing every fuse doesn't effect the "draw," then you have a lower-resistance-to-ground in an ungrounded circuit (like the starter) or the fuse box itself. For 300ma, look for green-crusties or oily dirt.

 

Thanks for the reply back. Since the meter maxes out, the actual value will be higher. I'll take better data . Yes I am measuring the draw by using my meter at the battery post. Since I have disconnected the power to the starter, there should not be a drain there. I need to check on the fuse box now that you mention it.
Thanks,
Matt

 

Just an update on this ...
I opened up the fuse box. On the battery leg of the 80A fuse there was a white wire and after some experimentation I deduced that the short was in this wire. I undid the wire bundle, basically tracing this wire on its path and noted a splice into the wire. Having disconnected the splice the short went away. I don't think this is factory as I don't think Toyota would would have used this method of a connection. I traced the spliced in wire back and noted that the wire in turn was connected to three other wires. Disconnected all three. Testing one at a time the short was in one of them (another white wire) and this specific wire controls the power to the instrument and I suppose engine start. At the time that I did this, my ohm meter measured close to zero OHM between ground and the white wire. A day later the resistance had increased to over 1K! Now the meter does not even register a short. I suppose I should open up the wire bundle going the reverse direction but this will be a tedious process made more difficult now that I cannot even get a short.

On a side note I borrowed a friend's Fluke meter to measure the current draw with the short. It must have been more than 10 amps as it blew the 10 amp fuse in the meter

 

Was the white wire on the battery leg of the 80A fuse unusually large? IOW: Is the insulation seemingly thicker, heavier, softer, than normal wire insulation? If so, that's a fusible link. Essentially, a wire that will burn through if the current through it gets too high. The WIRE will burn, but, theoretically at least, the insulation will protect the "stuff" around it. A long, thin, fuse, essentially.
You might want to trace it to it's far end, and ohm it end-to-end to be sure it hasn't burned through. If it has, do NOT replace it with a regular piece of wire. ONLY replace it with an OEM fusible link.
You might want to trace the spliced in wires to their far ends as well, and see where they go. ESPECIALLY the one that reads short. What is it attached to that might be shorted? Or is the short due to the insulation of the wire being worn away against something metal, the insulation chewed through by a critter of some sort (they love to chew insulation), something like that.
Once you get the short sorted out (eliminated), and you know where those wires go, if you still want them powered up, connect them to a fuse, either in the engine room (as Toyota calls it) fuse block, or the the one in the cabin. Splicing off a wire like they were is a bad way to do the desired task. A lot of the fuse blocks have empty slots you can slip a fuse into to provide a decent, fused circuit.

Good luck to you!
Pat☺

 

Yes the white wire on the battery side of the 80A fuse is a thick wire. Since I had opened up the bundle completely, I did confirm that the wire went to the alternator. I had also disconnected the wire from the alternator and had measured its resistance end to end confirming that it was good - at least as far as a meter could tell.

Going back to the spliced wires, I temporarily connected them back to the battery positive and started the engine. With the engine compartment warm, I turned the engine off and measured the resistance across the other white wire and I could see a short to the ground. Now I really need to open up the bundle that has the other white wire and trace where it goes. .

 

Going back to this issue after a while it appears that the alternator may be the culprit. I can measure resistance between the alternator body and its terminals.
Main terminal @ 97 K-ohms
Connector terminals
1 @ 6 K-ohms
2 @ 1.4 K-ohms
3 @ 73 K-ohms
I think on the connector terminals, terminal 3 is always hot (it is connected to the battery) and as such there should not be any resistance. Not sure about the rest.

 

Well replaced the alternator. Unfortunately this did not solve my problem. I still have a short. On the new alternator the only difference that I see is the resistance of terminal 3 to the body. It is around 2 Mega-ohms and of course it is a shiny alternator. Rats!

 

Yeah, you definitely need to chase down that short to ground. Might involve tracing the wire with the short visually. IOW: Start at one end, and visually follow the wire wherever it goes. Open up the wire looms, and follow it. If you have to, follow it by feel, IOW, take it out of the bundle.
It's a good idea to mark it as you go, so you don't loose it 1/2 way between two plugs. A small piece of tape, a little dab of white-out or bright red nail polish, just something so that when you accidentally drop the wire back into the bunch in the loom, you can find it easily, and continue your tracing. Mark it about every 2 feet or so. It will make your life a lot easier!

Look for anywhere the insulation might be worn, or cut, or whatever, exposing the wire inside. Rodents also love to chew on the wires in these trucks. Keep your eyes open.

Good luck, and let us know how things go for you!
Pat☺

 

Well after a week of chasing this down and in showing the issue to a friend, he proved it to me that all had been fixed with the replacement of the alternator. It appears that I had damaged my meter when I had first tried to diagnose the issue. He simply used a test light to show that no current was flowing with the motor off whereas my meter showed a current draw! I am relieved and at the same time annoyed with myself for not double checking the current draw by other means like a test light.

 

Just remember that to get a light to light up, it requires a specific amount of current flow, or more. Any less than the required amount of current flow, and no light. No light can indeed show no current flow, yes, OR it might, might, be showing a LOW current flow. Be careful of making a mistaken assumption regarding the light.

Pat☺

 

I hear you. I have left the battery connected for two days straight now. Thus far all seems to be OK. When I had the issue, the battery would run down completely overnight.