Short

[Klowded]

I have an 89 mustang and a few years ago a yellow wire with a rubber block that had four fuse linked wires coming out of it attached to the starter solenoid broke off at the rubber block. I pulled the yellow wire back inside the car and put it in a fuse block and life was good. Today the car ran for five minutes and died. It blows this fuse two seconds after I turn the key. I traced it back to the starter switch witch has another yellow wire next to it that runs to the original fuse box and everything there is fine. I changed the starter switch witch was sketchy but it still blows the fuse. Is there a negative wire in there I should be looking for?

 

[a91what]

There is a short in the system somewhere, take the fuse out and check for resistance with a DMM.

 

[jrichker]

Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.


Starter solenoid wiring for 86-91 Mustang

Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.

Choose the fuse according to the wire size.


Wire size current table:

18 gauge wire = 5-8 amps
16 gauge wire = 10-12 amps
14 gauge wire = 15-17 amps
12 gauge wire = 20-25 amps
10 gauge wire = 30-40 amps
8 gauge wire = 50-60 amps.

Keep in mind that the wire size in the chart is for the circuit itself, not the size of the fuse link. The packages of fuse link repair material you can get at the auto parts stores also will have a current rating on them.

Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.


View: http://youtu.be/uaYdCRjDr4A

Aircraft type circuit breakers are designed for low voltage DC applications and would be an excellent choice to replace fuse links. They come as a push/pull to reset button, and range from 1.5 amps to 60 amps and higher.

See http://www.aircraftspruce.com/index.php or http://www.wicksaircraft.com/catalogDetails.php or http://www.sacskyranch.com/ for circuit breakers and other items.

There is a store local to Orlando that does electronic surplus and has all kinds of circuit breakers. See www.skycraftparts.com That's where I get most of my wiring supplies. There may be a similar type store in your area

For free automotive electrical training, see Automotive Training and Resource Site . I have personally reviewed the material and it is very good.

PM me your email address and I will send you a complete Ford Factory 89 Mustang electrical diagram set. The zip file is 2.5 MB and is too big to fit through Stangnet's email gateway.

89 Mustang wiring diagrams zip package–

They are in a zip file format to reduce the size of the package. If you don't have Windows 7 or Windows 8, you’ll need WinZip or other Windows archive tool to extract them from the zip file.. See www.majorgeeks.com - Download Freeware and Shareware Computer Utilities for a free download.

The diagrams show the location area and the connectors are drawn to the same shape as those in the car.

You will need the Adobe Acrobat viewer which is also a free download – www.adobe.com/products/acrobat/readstep2.html - Adobe Reader download - All versions

 

[jrichker]

There is a short in the system somewhere, take the fuse out and check for resistance with a DMM.

Nice try, but the resistance of a automotive light bulb is very low until it is turned on and heats up. Figures like 3-4 ohms are common, or less if it is something like a headlight, taillight, or parking light. String two or three of these automotive light bulbs together in a parallel circuit and measure the resistance and it will be so low that a common DVM can't distinguish it from a real short to ground. The same thing is true of circuits that have motors like fans, windshield wipers and A/C compressor clutches.

The way to troubleshoot and locate short circuits is insert a meter that can capture peak current surges in series with the suspected circuit. Then use a circuit breaker in place of the fuse so that you can reset and troubleshoot it multiple times. The current surge is what blows the fuse.
OR
Simple way to find short circuits other that watching for smoking components; use a cheap compass placed next to the wire. See the video below to watch it work.


View: https://www.youtube.com/watch?v=HcPDc23ZLEs

 

[a91what]

Nice try, but the resistance of a automotive light bulb is very low until it is turned on and heats up. Figures like 3-4 ohms are common, or less if it is something like a headlight, taillight, or parking light. String two or three of these automotive light bulbs together in a parallel circuit and measure the resistance and it will be so low that a common DVM can't distinguish it from a real short to ground. The same thing is true of circuits that have motors like fans, windshield wipers and A/C compressor clutches.

The way to troubleshoot and locate short circuits is insert a meter that can capture peak current surges in series with the suspected circuit. Then use a circuit breaker in place of the fuse so that you can reset and troubleshoot it multiple times. The current surge is what blows the fuse.
OR
Simple way to find short circuits other that watching for smoking components; use a cheap compass placed next to the wire. See the video below to watch it work.


View: https://www.youtube.com/watch?v=HcPDc23ZLEs

I trouble shoot circuits all day long. 24v controls, 48v controls all the way up to 38k... I have multiple tools in my arsenal. If I were to trip a circuit on purpose things typically don't go well.

Pulling the fuses splits the circuit into two parts, if the circuit opens to ground you move to the next section of the circuit. Measure then remove the loads from that circuit (is light bulbs relays ect.) Once all the loads are removed the circuit should read open. If it does not you have narrowed the short down to that area.

The typical short will have less than 10ohms too ground, depending on wire size and length to the short.

I guess I should have expanded on my post further, I was balls deep in a process logic controller at the time.

 

[jrichker]

I trouble shoot circuits all day long. 24v controls, 48v controls all the way up to 38k... I have multiple tools in my arsenal. If I were to trip a circuit on purpose things typically don't go well.

Pulling the fuses splits the circuit into two parts, if the circuit opens to ground you move to the next section of the circuit. Measure then remove the loads from that circuit (is light bulbs relays ect.) Once all the loads are removed the circuit should read open. If it does not you have narrowed the short down to that area.

The typical short will have less than 10ohms too ground, depending on wire size and length to the short.

I guess I should have expanded on my post further, I was balls deep in a process logic controller at the time.

Thanks for the expanded explanation, it certainly makes more sense.

Disconnecting the loads was something that I left out since a circuit with no load doesn't draw current. Finding all of the loads in automotive circuits without a set of wiring diagrams is a hit or miss proposition. That's why the last item in my post was an offer for a set of wiring diagrams for an 89 Mustang.

In 12 volt circuits, a short sufficient to blow fuses is going to be a very low resistance. A 5 amp circuit has 2.4 ohms resistance, a 20 amp circuit has 0.6 ohms resistance. Very few people have anything beyond a cheap DVM, and measuring resistances that are very close to the value get you get by shorting the probe tips together can be an iffy proposition. There are a lot of people that struggle to interpret what they see displayed on the DVM readout. I can't tell you how many times that I tried to help guys use a DVM that I had never seen and that they didn't know how to use.

The fix for the above is the magnetic compass trick, since it is a yes or no answer. Either it points to the wire when power is applied or it doesn't. Your step of removing the load is a very important part of the process that I left out. The limiting factor is that you don't have it next to a big chunk of iron. They are also cheap - less than $10 if you shop carefully.

The circuit breaker is a standard automotive item, the Mustang uses one for the power windows and another for the wipers. The wiper one is 8.25 amps, and would be the best choice for troubleshooting shorts in most circuits. Make a pair of 16 gauge short test leads using 1/4" tab style quick connects and it is ready for use. Check the wiring diagram and make sure the circuit you are testing has at least 18 gauge wiring before using it.

 

[Phillip123]

Did ya try taking the fuse out?