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Chevrolet Repair/astro van taillights and dash lights fuse blowing

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QUESTION: My Astro Van is blowing the fuse for the taillight and dash lights. I removed all tail light bulbs and front signal bulbs, including marker lamps, checked the (electrical) plugs and wire for hot looking spots or bare wires, shorts etc. All bulbs removed still blows fuse.
Also unhooked the lighter assembly, still blows fuse. (everything unplugged)
I looked at the harness going back through the interior of the van, it doesn't seem pinched or restricted at all. Unhooked the dimmer switch and checked for visual signs of a short, nothing, it still blows with the dimmer unhooked, lighter unhooked and all bulbs out of affected circuits.
The head lamp switch looks brand new, also the dash light dimmer is new looking, gut i have owned the van 12 years and don't remember changing either of them (but probably have). They don't seem hot but the fuse blows instantly when i turn the lights on so its hard to say whether they are shorting internally.
At this point i am wondering if i should just try a new head lamp switch, but i will have to order one if i do. Thanks for your help.
jonny

ANSWER: HI JONNY,,WOW THIS IS A GOOD ONE...HAVE YOU LOOKED AT THE WIRING HARNESS TO THE CIGAR LIGHTER. I KNOW YOU SAID YOU UNPLUGGED IT, BUT FOLLOW THAT WIRE UNDER THE DASH. IS THIS THE CIGAR LIGHTER CONNECTION THAT IS UNDER THE DOG HOUSE [ENGINE COVER] ??? IF SO FOLLOW THAT POWER WIRE TO SEE IF IT HAS SHORTED OUT SOMEWHERE. I HAVE FOUND PROBLEMS IN THIS AREA IN THE PAST. IS YOUR DOME LIGHT WORKING OK ??? I AM NOT AT WORK SO I DO NOT KNOW IF THIS IS ON THE SAME CIRCUIT OR NOT,BUT IF THIS LIGHT IS NOT WORKING WHEN THE FUSE BLOWS CK THIS CIRCUIT AS WELL. I DO NOT THINK IT IS ON THAT SAME CIRCUIT BUT WORTH CHECKING INTO IT..IT IS STILL POSSIBLE THAT THE WIRING HARNESS IS GROUNDING OUT SOMEWHERE..YOU MAY WANT TO UNPLUG THE HARNESS GOING TO THE REAR OF THE VAN OR CK WHERE IT GOES THROUGH THE FIREWALL AS WELL TO THE FRONT.. BUT IF ALL THIS LOOKS GOOD I AM WITH YOU FOR A SHORTED HEADLIGHT SWITCH..I THINK AT THIS POINT IT IS FASTER AND CHEAPER TO INSTALL THE SWITCH RATHER THEN TRACE ALL OF YOU WIRING HARNESS CHECKING FOR A SHORT.. LET ME KNOW HOW THIS GOES FOR YOU AND GOOD LUCK TO YOU,,,TOM...PS I AM SURPRISED THAT NO STORE HAS THIS SWITCH IN STOCK..TRY YOUR DEALER...

---------- FOLLOW-UP ----------

QUESTION: Hey Tom thanks for the quick response!
I went right out and looked at the cig lighter power wire, followed it all the way to the fuse box, no pinches or anything there. Also it looks to be in great shape including the ends. It is the one under the dog house, yes. This is where i initially expected to find a problem.
It first happened when i hit a bump last night. That seems to suggest a short some where. So i put an ohm meter on the terminals for the fuse to see if either were grounded and one was. I assumed that was my short, but now i think that is not a good way to measure, what do you think of that?
The reason i think its not a good measure is that after reading your advice (and checking things) i went back and decided to see if i could get it to work enough to see if the switch gets hot. So i turned the switch on while watching the fuse bc it was blowing instantly. This time no spark/fuse blown, so i started putting bulbs back in one at a time to see if one blew it. None did, but one looked strange almost like the bright and dim filaments were touching. Also i couldn't get that one to go back into the socket and i know i was doing it right. I took a front bulb and put it in that socket and it worked ok. So i reinstalled all the bulbs except the blown one in the rear and tried it, still works. The HL switch isn't getting warm at all, the dimmer maybe just a little, but its a rheostat so that is probably normal right?
The dome light is working but that is on a different fuse. I tried to unplug the harness going either way but couldn't find any plugs so i visually checked as best i could and it all looks fine, not pinched or anything.
I know a bulb could have done this but i'm not convinced i have found the problem yet and its dark so i should wait until tomorrow to get a new bulb.
I will definitely follow up as i have found these kind of stories to be very useful. Any additional ideas you may have are welcome, but i will let you know how it turns out with a new bulb tomorrow, and if i have to try a switch or whatever. Thanks and i hope you have a great holiday season! Its awesome that you guys just help people fix their cars like this!

Answer
HI JONNY, YES A BULB COULD DO THIS IF IT WERE SHORTED..AS FAR AS CHECKING WITH A OHM METER THIS IS NOT A GOOD METHOD..A AMP METER WOULD TELL YOU IF THAT CIRCUIT IS DRAWING TO MUCH CURRENT BUT NOT WHERE THE PROBLEM IS....YOU WILL NOT LIKE THIS BUT WE SOMETIMES WILL PUT A HIGHER AMP FUSE IN AND HAVE ONE GUY IN FRONT AND ONE IN THE REAR AND WATCH TO SEE WHAT THE LIGHTS LOOK LIKE WHEN WE TURN THEM ON..ANY DIM LIGHTS OR SUPER BRIGHT WE CK THAT CIRCUIT..THE OTHER THING I DID NOT SAY LAST NIGHT WAS WHAT ABOUT THE PRINTED CIRCUIT TO THE DASH BOARD..WE HAVE FOUND SOME OF THEM SHORTING OUT AS WELL..SO IF THIS LIGHT IS NOT THE PROBLEM,REMOVE THE DASH FACE AND TURN THE LIGHTS ON AND SEE IF THIS IS IT...LET ME KNOW HOW IT GOES AND HAPPY HOLIDAYS TO YOU AS WELL...GOOD LUCK TOM...

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TOM SHEETS

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PLEASE READ ALL OF THIS BEFORE ASKING ANY QUESTIONS. IF THIS CHEVY SECTION IS MAXED OUT.YOU CAN REACH ME IN THE OLDS/BUICK SECTION. Will answer questions from 6:00am to 10:00pm all days [EST][[[ NO DIESEL OR PAINT QUESTIONS]]] will answer all 1965 to present QUESTIONS ON ALL GM'S on mechanics of these cars. Keep in mind i am not there in person i am going on what you are telling me !! PLEASE IF ASKING A QUESTION GIVE ME AS MUCH INFO AS POSSIBLE. THE MORE THE BETTER. SUCH AS YEAR,MAKE,MODEL,ENGINE SIZE. THIS WILL HELP ME HELP YOU. I will not be able to answer all questions because of some situations that i would really need to be there and see things for myself,such as electrical issues. In many cases i would need wiring diagrams. I can also give you an estimate on what the cost would be at our repair shop as an idea to help you. Keep in mind that my answer is ONLY MY ADVICE,ck with your mechanic as well.. >> THANK YOU, TOM..

Experience

I have been a ASE certified master mechanic for over 30 years and certified IN ALL 8 CATEGORIES,[engine repair,engine performance,auto trans,manual trans,clutches,steering and suspension,brakes,electrical systems,heating and air/cond. I am also a state CERTIFIED inspector for over 30 years. I do computer work [pcm]fault codes,pcm flashing,state inspection monitor readiness,repairs on exhaust,fuel service,[injection and carburetor,] charging system problems, running issues,alignments,frame problems,tire balance,struts and of course standard and anti-lock brakes.

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nys state auto repair industry and ase group.

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high school,4 years of tech school,and many many hours of auto training with many gm classes and aftermarket training classes..

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ASE MASTER TECH CERTIFIED IN ALL 8 CATEGORIES.NYS INSP LICENSE AND A/C CERTIFIED

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