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78 SS 4speed 305
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Discussion Starter #1
78 SS. The 5 amp fuse for the instrument lamps blows instantly every time the headlight switch is pulled turning the lights on. Headlights work as should, courtesy lights work properly via dimmer switch turned all the way left.
Problem started by having only a couple bulbs that were out, so i pulled the dash replaced all the bulbs at once with napa 168 bulbs, test before re install of dash and now none work, beside the ones on far right for brights, seatbelt, parking brake. So then i replaced the headlight switch(It was original and corroded), no difference. Was also troubleshooting gauges etc so replaced the PCB and cleaned all the contacts etc. Have cleaned an re attached multiple grounds( above parking brake, the two at rear bumper, motor to firewall, battery to inner fender)...
Symptoms seem as a short/pinched wire?? Ive visually checked just about all i can see...
 

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do you have an electrical schematic for your model? do you have and know how to use a multimeter to test/trace circuitry?
 

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Since it is blowing the instr fuse, that tells you it is on the output side of the fuse box. Grey wire feeds all the dash lights from the fuse box. Try unplugging the connector from the dash circuit board and see if it still does it. That should help you narrow down where the problem is.
 

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78 SS 4speed 305
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Discussion Starter #4
Since it is blowing the instr fuse, that tells you it is on the output side of the fuse box. Grey wire feeds all the dash lights from the fuse box. Try unplugging the connector from the dash circuit board and see if it still does it. That should help you narrow down where the problem is.
Will give this a check tomorrow, thank you. So with PCB connector unplugged, if fuse no longer blows(or does), what is that telling me?
 

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78 SS 4speed 305
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Discussion Starter #5
do you have an electrical schematic for your model? do you have and know how to use a multimeter to test/trace circuitry?
would have to google a schematic. Have a multimeter but knowledge of use is limited to what i read in instruction manual or online haha
 

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Or check what is available on El Camino Central.
Wiring Diagrams 59-60, 64-88
 

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So with PCB connector unplugged, if fuse no longer blows It is telling you the problem is in the circuit board.

(or does), what is that telling me?

If it still blows it is telling you the problem is in the grey wire from the fuse panel to the circuit board connector.
 

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78 SS 4speed 305
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Discussion Starter #8
So with PCB connector unplugged, if fuse no longer blows It is telling you the problem is in the circuit board.

(or does), what is that telling me?

If it still blows it is telling you the problem is in the grey wire from the fuse panel to the circuit board connector.
Thank you. So went an unplugged the PCB and fuse no longer blows. PCB is brand new, contacts on the male connector were cleaned prior. 🤷‍♂️
 

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78 SS 4speed 305
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Discussion Starter #9
Also upon pulling the cluster all the way out to view PCB, found this. The circuit line for the lights has burn marks :(. What could cause this? Probably when I put a 10amp fuse in at one point cause it’s what I had around, and upon doin so wizard smoke and scents arose from behind dash 🤦🏻‍♂️
5DC47940-1A16-4516-BEC1-30270309B974.jpeg
 

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Yeah that burned line looks like it is for the lights. Awhile back I remember seeing a YouTube video on how to fix that burn and as I recall they used the same stuff that you use to repair rear window defroster
 

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Trace/follow the circuit around the pcb and find where the burn stops. that is where the short to ground is.
 

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78 SS 4speed 305
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Discussion Starter #12
Y’all rule, thank you! Also found this duct taped behind radio, any idea what is?
E8BA2DF4-0C0B-49E2-B7A9-DF9F77DBDA2E.jpeg
 
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