Electrical 92 GT Convertible - Fuse 13 Continuity Testing Question

Blown88GT

Founding Member
Nov 13, 1999
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Palm Beach Gardens, FL
1. While I'm waiting for the tester to come ...
2. I did unscrew the fuse panel and bend it out of the bracket , as it laid down it did raise the ohms for Split Second up to 17 from around 7. But no go when I wiggled it. Maybe from me shifting it. Who knows.
3. My one question, well more bouncing it off you, is the circled harness location in the attached, s208? Pretty sure it is based on the attached location index.
4. Which brings another question I guess, that tool needs to be directly on the wire... What's the easiest way to access that area? So I can actually open it up and get to the wires. I have not gone that deep with the interior. The upper center console section comes out as one piece I believe, no? Correct me if im wrong. Thanks.
1. I got my tester yesterday. While you're waiting for yours, you need to make a fuse box adapter. Take a blown fuse (you have many), solder 2 wires to the test points on top of the fuse. This is what the "tester fuse" alligator clips will connect to.
2. I don't know.
3. Looks like it is.
4. I didn't open the "tester fuse" up, it's a thermal automatic resettable circuit breaker. The "tester meter" works by magnetic induction. You don't have to open any splices or bundles, just yet. You connect the "tester fuse" to the adapter you made which plugs into #13. You will work with the meter back from the fuse box (#13). If there is no short, you won't see anything. Make sure the dimmer is set for "dome light on". You want to force the "tester fuse" to trip, if the short exists. You don't need the test light, the dome light will serve as a test light.
 
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1. I got my tester yesterday. While you're waiting for yours, you need to make a fuse box adapter. Take a blown fuse (you have many), solder 2 wires to the test points on top of the fuse. This is what the "tester fuse" alligator clips will connect to.
2. I don't know.
3. Looks like it is.
4. I didn't open the "tester fuse" up, it's a thermal automatic resettable circuit breaker. The "tester meter" works by magnetic induction. You don't have to open any splices or bundles, just yet. You connect the "tester fuse" to the adapter you made which plugs into #13. You will work with the meter back from the fuse box (#13). If there is no short, you won't see anything. Make sure the dimmer is set for "dome light on". You want to force the "tester fuse" to trip, if the short exists. You don't need the test light, the dome light will serve as a test light.

Very cool. Thank you sir.

Enjoy the weekend!!
 

WillWho?

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Apr 1, 2018
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Hope y'all don't mind me jumping in here. There are two other components in common with the dimmer that also energize some fuses and some fuses energize those components.

When a light is dimmer, generally it means voltage is dropping either at or before that light. That means the intermittent short is likely a close arcing short. It is not likely a direct short which is why it takes a bit to heat the fuse (breaker) and blow it.

The Multifunction Switch (MFS) and Ignition Switch Module (ISM) are both common to the dimmer and head light switch. Both oh those have trouble shooting guides in the EVTM. Both are known common points of failure.

Remove the lower steering column. The MFS is by the driver's left knee and the ISM by the right knee. The ISM is the most likely point of failure. The plastics get brittle with age. There is a full blown recall on those, but it is not worth the time taking it to Ford. The part is under $20 at local parts stores. It is about a 20 minute job. I believe you need a security torx driver to remove it. (It has been a while.) Be careful when you first touch the ISM, they like to crumble into a gazillion pieces with some getting your eyes. Sometimes just the retaining clips break and you can push the connector tighter. Zip tieing the connector to keep it from coming loose is OK for a day or two. However, you are risking yoyr life, or even worse your car burning burning to the ground. The rest of that brittle plastic is just waiting to crumble.

The MFS has a very good troubleshooting guide that will let you know if it has an internal failure. Having one fail is not as common as the ISM.

For the main/fog switch, you should probably make a modification that is quite simple to emilinate the poor design of that entire circuit. I will resist aiming a dig at automotive electrical engineers. ;)

Here is a diagram on how to modify the fog circuit by adding a relay. This is the easiest fix. BTW, rather that letting the fogs energize from the low beam circuit, you can energize from the parking lamps or an accessory fuse panel. That way you can have fogs with just parking light, or fogs with just fogs. Just run a 12g wire from the relay to the fogs, and a 12g wire from the 12V source to the relay. The factory wire on the relay trigger is sufficient since the amp load no longer passes through that wire. You could add a relay for the headlights too, and completely remove the amp load from the switch. The headlight/fog switches were TSB's for 87-93. The factory never fixed the problem. Even when my 89 caught fire on a trip home from New Orleans. Fortunately, I do not panic and removed the hottest fuse as I moved into the emergency lane. I made a field expedient modification (aka MacGuyver) to have headlights the rest of the trip. Ford had not issued the TSB and I made the repairs at my expense. Which was fine, I added relays and had fogs available with parking lights.

I am not an electrical engineer. I am a retired aircraft instrument mechanic (analog/electronic), former AC/DC theory instructor, advanced circuitry instructor, micro-miniature solder instructor, multilayer circuitboard repair instructor, aircraft instrument calibration specialist (analog/digital), & forensic aircraft instrument analyst. This was for aircraft that travel at speeds from slow to Mach 2.5 and faster.

2018-05-28 01.33.35.png


Another problem is the courtesy light switches in the doors and the hatch. The internals get oxidation, wire insulation gets brittle, and those lights tie into the dimmer. So if the ISM and MFS check out OK, take a look at those.
 
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Hope y'all don't mind me jumping in here. There are two other components in common with the dimmer that also energize some fuses and some fuses energize those components.

When a light is dimmer, generally it means voltage is dropping either at or before that light. That means the intermittent short is likely a close arcing short. It is not likely a direct short which is why it takes a bit to heat the fuse (breaker) and blow it.

The Multifunction Switch (MFS) and Ignition Switch Module (ISM) are both common to the dimmer and head light switch. Both oh those have trouble shooting guides in the EVTM. Both are known common points of failure.

Remove the lower steering column. The MFS is by the driver's left knee and the ISM by the right knee. The ISM is the most likely point of failure. The plastics get brittle with age. There is a full blown recall on those, but it is not worth the time taking it to Ford. The part is under $20 at local parts stores. It is about a 20 minute job. I believe you need a security torx driver to remove it. (It has been a while.) Be careful when you first touch the ISM, they like to crumble into a gazillion pieces with some getting your eyes. Sometimes just the retaining clips break and you can push the connector tighter. Zip tieing the connector to keep it from coming loose is OK for a day or two. However, you are risking yoyr life, or even worse your car burning burning to the ground. The rest of that brittle plastic is just waiting to crumble.

The MFS has a very good troubleshooting guide that will let you know if it has an internal failure. Having one fail is not as common as the ISM.

For the main/fog switch, you should probably make a modification that is quite simple to emilinate the poor design of that entire circuit. I will resist aiming a dig at automotive electrical engineers. ;)

Here is a diagram on how to modify the fog circuit by adding a relay. This is the easiest fix. BTW, rather that letting the fogs energize from the low beam circuit, you can energize from the parking lamps or an accessory fuse panel. That way you can have fogs with just parking light, or fogs with just fogs. Just run a 12g wire from the relay to the fogs, and a 12g wire from the 12V source to the relay. The factory wire on the relay trigger is sufficient since the amp load no longer passes through that wire. You could add a relay for the headlights too, and completely remove the amp load from the switch. The headlight/fog switches were TSB's for 87-93. The factory never fixed the problem. Even when my 89 caught fire on a trip home from New Orleans. Fortunately, I do not panic and removed the hottest fuse as I moved into the emergency lane. I made a field expedient modification (aka MacGuyver) to have headlights the rest of the trip. Ford had not issued the TSB and I made the repairs at my expense. Which was fine, I added relays and had fogs available with parking lights.

I am not an electrical engineer. I am a retired aircraft instrument mechanic (analog/electronic), former AC/DC theory instructor, advanced circuitry instructor, micro-miniature solder instructor, multilayer circuitboard repair instructor, aircraft instrument calibration specialist (analog/digital), & forensic aircraft instrument analyst. This was for aircraft that travel at speeds from slow to Mach 2.5 and faster.

2018-05-28 01.33.35.png


Another problem is the courtesy light switches in the doors and the hatch. The internals get oxidation, wire insulation gets brittle, and those lights tie into the dimmer. So if the ISM and MFS check out OK, take a look at those.
Aawesome feedback! The ISM is brand new and I have the old one that still works as well. I'm wondering if it's the multifunction switch. I'm going to look in the manual for the troubleshooting.

it's definitely something that is heating up and then it goes bad. So the switch sounds possible.
 

Blown88GT

Founding Member
Nov 13, 1999
2,186
529
164
Palm Beach Gardens, FL
...For the main/fog switch, you should probably make a modification that is quite simple to eliminate the poor design of that entire circuit. I will resist aiming a dig at automotive electrical engineers.

Here is a diagram on how to modify the fog circuit by adding a relay. This is the easiest fix. BTW, rather that letting the fogs energize from the low beam circuit, you can energize from the parking lamps or an accessory fuse panel. That way you can have fogs with just parking light, or fogs with just fogs. Just run a 12g wire from the relay to the fogs, and a 12g wire from the 12V source to the relay. The factory wire on the relay trigger is sufficient since the amp load no longer passes through that wire. .

I am not an electrical engineer. I am a retired aircraft instrument mechanic (analog/electronic), former AC/DC theory instructor, advanced circuitry instructor, micro-miniature solder instructor, multilayer circuitboard repair instructor, aircraft instrument calibration specialist (analog/digital), & forensic aircraft instrument analyst. This was for aircraft that travel at speeds from slow to Mach 2.5 and faster.
.
Nope, don't mind you jumping in at all. You might have missed the explanation of the dimmer providing reduced voltage, but that's OK.

You don't need to add a relay or any wire if you follow this even simpler 2 minute procedure. Literally will take you longer to read it than to do it.
https://www.stangnet.com/mustang-forums/resources/87-93-gt-fog-lamp-main-light-switch-fix.59/

I am (was) an electrical controls engineer & I designed some of the aircraft control (DEECs & FADECs.) diagnostic & simulation equipment for F15, F16, F22, F35.

Look familiar?
PHOTO_Engine-and-Control-Systems_1-Electronic-Engine-Controllers.jpg
300px-F-35A_Lightning_II_Joint_Strike_Fighter_Powerplant_on_display_at_Centenary_of_Military_A...jpg
pratt-whitney-f135-turbofan-jet-aircraft-engine-F7DEEC-1.jpg
 
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What does the current (old) switch & plug look like? You can tell by looking at it if it was overheating. The switch is not only a switch but a thermal circuit breaker.


I will have to look for the old one it's put away amongst all the other old Parts. I replaced it because I had a misfire which was totally unrelated because of the bad head gasket. But initially when I inspected it I remember it looked brand new as the car itself has been garage its entire life only has 49,000 miles it's pretty mint.

I will test it to be sure. As an update though I pulled the LCD illumination relay. It definitely sounds like Something's broken loose in there. It rattles pretty good. Loud like a busted light bulb.

They're like 20 bucks I think so I'm probably just going to order a new one.
 

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Well I have an update. it's a pretty different one I'm sure but after starting my car because it seemed the short randomly resolved itself even after using the short tool and it did not trigger any thing. Lights worked all of a sudden.

Long story short, I had wrapped my catalytic converters because they were placed wrong when my smog guy had them installed. Right below the fire wall under the speedo cable (melted 2 cables)....Long story short the heat transferred to the straight pipe after the cat, right under the center console.... wires right under the center console and the socket for the lighter, the mirror Etc are toast, it got so hot that the paper and the carpet started to smoke. It did it once before but I assumed it was the wraps.

So at this point obviously all the wires have melded together and I found the problem of where my short was (haha).

Talk about being deflated let me tell you man (hence beer on the tool box) after over 200 hours between the new fuel line new fuel pump all new sensors cleaning the entire block you name it literally changed almost everything to try to make it perfect. I know it will never be perfect. But I just want to drive the damn thing.


Now I have to pull the seats, slice the carpet, fix the wires, cut off the cat wrap. I re-routed the speedo cable so it should be fine.

I guess the bright side is it did fire up after the second time I had to redo the head gaskets so that's a plus. But what can you do. Thanks for the help guys.

End result: Melted wires, under the center console, from heat wrapping the cats, that had been placed to close to the firewall, speedo cable area, which then heat transferred to directly under the center console.
 

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jrichker

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I am certainly glad that you found the problem. The center console was one of the areas that I thought might be suspect, since you had removed the instrument cluster and most of the other wiring that could have caused problems.
 
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Blown88GT

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Makes me wonder if that's where my intermittent short might be. The under hood light thing is probably just a coincidence.
Probably best to pull the top off the center console & have a look. Never had the top off it, doesn't look too hard to get to. 20 years ago, I had a lot of heat coming out the console for 1 day. It went away & never came back. There was a recall on the cats, Ford Replaced them. Sold them as like-new when replaced with hi-flow cats.
 
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Makes me wonder if that's where my intermittent short might be. The under hood light thing is probably just a coincidence.
Probably best to pull the top off the center console & have a look. Never had the top off it, doesn't look too hard to get to. 20 years ago, I had a lot of heat coming out the console for 1 day. It went away & never came back. There was a recall on the cats, Ford Replaced them. Sold them as like-new when replaced with hi-flow cats.

So it turns out it was my exhaust cut outs. After 1000 miles and sitting there running with no air so many times while I tried getting it to run right, the inner parts finally baked enough to smoke and melt. Melt the paint on the under side.

If I line the under side with heat reflective tape and heat wrap the cut outs, do you think I will be good on the heat moving forward?

Also, I saved the passenger side wiring but the driver side harness is toast. The wires are good where I cut back too.

Any of you guys know where I can drop someone 20 or 30 to cut their 92 harness and ship it? Its so melted I cant tell which grounds run where etc. Buying a new harness would be so easy haha
 

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The Foxbody gods are with me. Never once have I gone to pick your part and do they have anything I needed. Sure enough they have a 92 white Mustang GT convertible. And sure enough the wire harness was there. $10 later including a dimmer switch LOL
 

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dstewart291

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my fog/head light switch connector is quite melted also previous owner did not fix, i am terrible with electrical stuff want to fix but man all the wiring and routing them to correct to be honest confuses me lol, but i am searching through these to find the way to do it. on top of getting LED fog bulbs to help reduce consumption. just got her maybe 6 months ago? if even that long sat for 8 years so been going through what i can find just did the drums wanted to break everything in sight... she added an aftermarket cluster in, hated it so that had to go finally got a year correct one and then came across my nicely melted connection lol