Electrical gurus, please step inside...UPDATE - PROBLEM SOLVED!

Back story...
2002 f250 Super Duty, 7.3 Powerstroke, ZF-6, Supercab, long bed, a beautiful beast.

Today on the way to WORK (can I say cuss words here???) I noticed that I had no dash illumination. Of course, upon arrival and inspection, I had no running lights, either. I poked around in the dark and replaced my blown "Fuse #17" which, according to the owners' guide, feeds "exterior illumination". As soon as I hit the main light switch, it failed again. I'm trying to arrive at a reasonable explanation here, since only a couple of things have changed!

2 weeks ago, I replaced the clockspring and multi-function switch for directionals/wipers/4-ways, etc. No problems. Last week, I replaced a faulty electronic flasher relay for the directionals. Still no problems. Last night, I pulled the door panels and installed a new passenger-side electric mirror, mirror control switch, and 2 front door speakers. Piece of cake.

There were no problems noted until this morning. As explained above, I had the door panels removed, and the only item remotely associated with lighting were those silly little fixtures behind the reflectors in the doors that are there for safety, I guess. Until then, I thought they were just reflectors, but both bulbs were burned out behind them. The damned things aren't even mentioned in the wiring diagrams...

Anyhow, where would you look first for a DEAD short??? 'Cause that's what I've got. And my "spare" vehicle has it's troubles, too...at least the lights work...

Any assistance appreciated! Even bad ideas or wild guesses will be considered. I have Monday & Tuesday off, so I'll be diggin' in. Thanks in advance!

Dave

I had a similar problem with my truck. I started to back track everything, electrically, I had done to the truck. Mine turned out to be a shorted light bulb. I had NEVER seen a light go out to a short, and I am 68 years old and have been messing with electrical stuff for most of my life. It took my almost three weeks of looking (not all of this time frame) to find the problem. I started to disconnect the clearance lights on the cab and I found it. Don't give up you will find it...

DaveBen said:

I had a similar problem with my truck. I started to back track everything, electrically, I had done to the truck. Mine turned out to be a shorted light bulb. I had NEVER seen a light go out to a short, and I am 68 years old and have been messing with electrical stuff for most of my life. It took my almost three weeks of looking (not all of this time frame) to find the problem. I started to disconnect the clearance lights on the cab and I found it. Don't give up you will find it...

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Thanks...that's my next step. Keep digging until something reveals itself!

I have an old Airpax 20 amp breaker from a long gone Ten-Tec transceiver that I might rig up in line to save on fuses! (KK6TNI de KD7DS... always good to find a fellow op on the 'net!)

I refuse to mess with VSM systems.
I would disconnect batteries, put a ohm tester with the buzzer on the shorted circuit, and start pulling bulbs.

KD7DS, yes it is. But most in forums don't acknowledge HAMs.

KK6TNI

I would look at the headlight switch also.

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DaveBen said:

KD7DS, yes it is. But most in forums don't acknowledge HAMs.

KK6TNI

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Just happened to notice the call in your signature! 73!

And thanks for the ideas. I have the next 2 days off, so you can guess where I'll be spending my time.

IDIoit said:

I refuse to mess with VSM systems.
I would disconnect batteries, put a ohm tester with the buzzer on the shorted circuit, and start pulling bulbs.

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Not sure what VSM is...I'm not a fan of chasing any electrical problems in vehicles. Wiring harnesses are hiding everywhere, and rub against all manner of steel parts. Your recommendation was to be my next step anyway...check continuity to ground every place I can! That "BROWN" wire goes a lot of places!

79jasper said:

I would look at the headlight switch also.

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I read elsewhere that the switch is a notorious problem, most notably the rheostat that dims the dashboard lights. I'll be looking closely at that, too.

Yup. I just wasn't sure if it was still a problem on the SD trucks as it was the earlier trucks.
I have the exact same thing happen on my 94 with the headlight switch. Unplug it and look at the plugs also.
Also at another point had something happen with my turn signal switch that made it blow fuses. I took it apart and cleaned it.

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VSM Vehicle Security module
it replaced the GEM
basically they control different functions of the interior and exterior additions.
I know the GEM systems, more than I want to lol

IDIoit said:

VSM Vehicle Security module
it replaced the GEM
basically they control different functions of the interior and exterior additions.
I know the GEM systems, more than I want to lol

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I don't believe my truck is equipped with that. It does have an aftermarket alarm/security system of some type, but I don't know much about it...installed by a previous owner. I'll try to get deeper into the wiring manual when I have more time & daylight!

in 02 they all went to VSM from GEM

IDIoit said:

in 02 they all went to VSM from GEM

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So, am I to assume that my lighting is controlled by some sort of computer module, rather than battery voltage and an inline switch? It's rough wrapping my old mind around that concept...and it will make diagnosis an even larger nightmare! I'll sleep on it. Morning brings out the best of me...and the tools...

PROBLEM SOLVED!

Wired up an old 18-amp DC circuit breaker to save on fuses. Melted the plastic off a bad fuse with a heat gun, soldered a couple wires to the blade contacts, and squeezed on a pair of connectors to mate with the breaker, and started pulling bulbs everywhere. No luck...still blowing the breaker with no bulbs inline. Pulled the light switch, identified the wire feeding the running lights, and checked for shorts to ground. Nothing - all good open circuits. Jumped the incoming power to the switch to the lighting circuit wire with a paper clip...all lights work, breaker holds! Guess what? The switch is boogered up! Upon further inspection, it rattles, too. Not good.

60 bucks and change on Amazon Prime for a Motorcraft swich, guaranteed here by tomorrow. Installs in about 20 seconds. Beats the 3 hours of diggin' around this morning (in drizzling rain) to diagnose the stupid thing! It was just a coincidence that it went south the day after I was into a lot of other wiring in the doors, but it sure had me scratching my head.

Thanks for all the input, gentlemen! This forum is excellent, and I've learned a lot here. I really should pay up for a membership...(SOON...finances permitting) since I'll probably rely on the gurus here more in the days to come! I really love this truck and I intend to run the wheels off.

Cheers!
Dave