Finding a short, where to start?

[steve_mk3]

Help- ( sorry for the long post, trying to provide all the info as possible)
I dont even know how to approach this problem.

After finshing the engine replacement, the brakes, the steering, finally got the exhaust connected up, it was time to deal with the battery. I have been jump starting the car and the Altenator would get very hot when the car was running. I put a new battery in yesterday afternoon, started right up. When I hooked up the battery there was a large spark that arked between the battery terminal and wire connecting so I thought something was wrong right then. I ran the car for a couple of minutes shut it down and came back like 3 hours later. when I opened the door the light were dim, and the battery would not even turn the starter over :icon_surp .

Now I am thinking I must have a short somewhere, but how do I even start to find out where? do I pull all the fuses from the main box on the firewall then use a VOM to see which circuit is connecting to ground? If I fried the alt how can I test that?

I need some help in starting the diagnosis.

As always your help and ideas are appreciated!

Thanks

Steve

 

[88turboma71]

hey steve how is it going, i am dealing with a problem of my own, so i know how u feel, with your problem what i would check first are my battery terminals make sure they are good, start of there, clean them, check your power cable coming off of the battery, make sure its not caught anywhere on its way to the starter, check the ground cable that goes to the block down by the j tube, check for some blown fuses, usually thats a good indication of wether u have a short or not, if u do u will most likely blow a fuse in that circuit, check that out first then post what u find or dont find

jorge
good luck

 

[bluemax]

Do you have an huge aftermarket stereo amp?
They draw a lot of current even at idle. And that circuit thats suppose to turn them off when the head unit is off never seems to work.

 

[steve_mk3]

Thanks for the replies-
Bluemax- no big stereo and the unit that is in there is powered off with the factory power circuit.
Jorge- New battery, terminals on the + and - wires. I seperated the wire that goes to the starter and the white one that goes to the main fuse box. Checked the wire to the starter with a Multimeter, no short to ground there. The white wire does show a short back to ground. So I looked at the TSRM, pulled the Main fuse the 40 amp AM1, the 30 amp AM2 and the 15 amp efi fuse. Could not get the 100 amp ALT fuse out. I also pulled the HEAD rely out. With all of that pulled I figured that the white wire should no longer have any path to ground. It still shows as a short! I checked from the one side where the fuses would go on both am1 and am2 and both short back to ground. On the oter side of am1 and am2 there is no short back to ground. So my problem appears to be between the main fuse box and the wire that goes back to the battery. I still need to get the 100 amp fuse out and find a digram of the fuse box itself.

Is it possible that the fuse box itself is bad?

Steve

 

[bluemax]

The fuse boxes won't have a short in it.
It just has the wires going in to the fuse and relay terminals. The box just holds these terminals for the fuses and relays. There's no ground wires and its made of plastic. The ground wires would be on the other side of the electrical component that the box is supplying power to.
So the chances of the box being a problem is very slim.

 

[steve_mk3]

Well it would help if I was using the correct TSRM. The 90 and 88 are very different. I have it norrowed to the black wire that runs off the 100 amp fuse and it is not in the circuits that are hooked up to AM1 or AM2.

The wire diagram that is in the Chiltons justs SUCKS!!

Any sugestions on where to get a 88 diagram?

 

[Idealsupra]

The fuse boxes won't have a short in it.
It just has the wires going in to the fuse and relay terminals. The box just holds these terminals for the fuses and relays. There's no ground wires and its made of plastic. The ground wires would be on the other side of the electrical component that the box is supplying power to.
So the chances of the box being a problem is very slim.

well this is relatively correct...however... you have the wrong idea

if you believe you have a short the fuse box should be the FIRST place you start. if you had a short it WILL blow a fuse or two...this is how you find out what circuits the short is on...

simply take a test light and with the key in the ON position do a test on each of the fuses on the panel... hook your test light to ground first and test them... then hook it to positive on the battery and test them... make sure youre getting the light to light up when its supposed to.

when you find one that doesnt work pull the fuse out an dsee if theres visable breaking the fuse... 95% of the time a blown fuse is obvious...

this will narrow your search significantly.... now you can find the circuits you need to track down the short on....BUT if what you said is true...YOU caused whatever short you think you might be having...so you might simply have to replace the fuse(s) that you blew and youll be fine.

otherwise whip out the tsrm and get to checking the circuit with all of the easily accessable points first....

hope that helped and report back with your findings...

 

[MDCmotorsports]

Just out of a wild guess.... Check to make sure you don't have the ground strap on the starter and the starter strap on the ground or ANY POSSIBLE way they are connected to each other.

Also, IIRC the 100amper is bolted in.

 

[bluemax]

I'm looking at my '87 TSRM.
Power circuit A runs off the 80A fuseable link ALT from the battery. It powers:
Alternator
Rear Window Defogger
Stop Lights
Tail Lights
Fog Lights
Dome Lights

You do have the dome light turned off? I've left mine on before, but it takes a couple of days to drain the battery.

 

[steve_mk3]

spent the last 5 or so hours trying things.
so the large wire that connects to the ALt will show a short to ground. I disconnected the black wire from the 100 amp fuse so now none of the circuits that run off of that leg show short to ground. I have pulled ALL the fuses out of the car( fuse panel under the dash and the one on the drivers side). It still shows a short to ground.

None of the fuses are blown. ( although some are now broken)
bluemax, is the 87 tsrm the same as the online one? I cant find a good wire diagram.

 

[bluemax]

The basics wire diagram and format is the same. But there are some differences in certain places.
I don't have a scanner so I can't scan it for you.

I forgot to mention that the circuit also supplies power to the ABS computer and condensor fan. (Sorry I missed that.) And you problem could be in power circuit B which branches off A.
Remember that some circuits always has power so it will always show a short. Like the ABS computer.

I would think that the alternator would show ground at the power side (black wire) when the engine is off. The voltage regualtor is part of the alternator assembly and may be bad.

 

[steve_mk3]

bluemax Ideal and MCD-
Thanks you all for your help.
I have not tracked this down fully yet.

Bluemax- I agree that the problem is with the A or B power circuits. I have already eliminated the ABS and CDS fuses, so the short is not part of that leg off of the circuit.

I think the remaining items runn of the fuse panel located by the drives side foot, is that correct?

I have pulled the black wire off of the alt and isolated it but untill i start unraveling the harness I am not sure that I will be able to further norrow down the problem.

Thanks
Steve

 

[steve_mk3]

Problem solved

There are two black wires running off of the alt power.
One wire powers the fuse block in the engine compartment, the second wire runs power to the fuse block in the interior drives side panel.

By seperating these ciurcuits I was able to determine that the problem was in the circuit that ran to the interior fuse block.

I had already removed all the fuses but did not pull the circuit breakers or relays. When I pulled the circuit breaker for the rear defroster my short was gone. I then knew the problem was in the circuit for the rear defroster. I put the breaker back in and tested the relay, and finding that it was not working and keeping the circuit closed.

So the relay being bad, resulted in the rear defroster staying on discharging the battery.

I did recieve the 88 Wire Diagram, now just need time to scan it and a place to host it.



Thank you all for you help.


Steve