The turn signal fuse on my 87 gt keeps blowing. It pops as soon as I start the car. I have the dash all off. Where is a good place to start to find this short?

I would suggest that you start by removing all the bulbs associated with the system. Then see if the fuse blows. If not, then replace a bulb at a time until the fuse blows. That will be your trouble shooting starting point.

If the fuse still blows with the bulbs removed them you have a bigger issue. You will have to refer to the wiring diagrams.

[This message has been edited by Cajun (edited 09-23-2018).]

quote Originally posted by Cajun: I would suggest that you start by removing all the bulbs associated with the system. Then see if the fuse blows. If not, then replace a bulb at a time until the fuse blows. That will be your trouble shooting starting point. If the fuse still blows with the bulbs removed them you have a bigger issue. You will have to refer to the wiring diagrams.

The fuse blows with out switching on the turn signals or putting it in gear (manual transmission) all I have to do is turn the key and it blows. I’m thinking it’s something with the wiring possibly. I’m not sure what trouble areas to look at to find the short. This is a 3800 engine swap and I’ve only recently had this problem. Currently the whole dash is off with nothing looking shorted and the plug next to the stock battery location looks ok too. What else is left?

Makes sense, the circuit is only receiving power when the ignition switch is in run/bulbtest/start.

As long as the "turn hazard switch assembly" isn't the part that is shorting internally, the short wouldn't be any of the blinker lights, or the circuits to them; they are out of the circuit until you physically flip the switch for left, right signal (look at the circuit, you can see how I highlighted the flow of power). It seems you can rule out/in the turn signal switch, the circuitry after it, and the flasher unit by simply removing the flasher. If after you remove the flasher and the fuse still blows, that isolates a whole lot of the circuit; and would mean that the short may be in the "back up lights" section for your hunt for a short, as that is spliced off that circuit before the flasher... If the fuse continues to blow after removing, then you know the short is on the side of the flasher, etc...

Here's the diagrams for you to look at to help you along... I highlighted the wire colors, while also guiding the flow of power to you, so that you a basis of what wires you should be focusing on while you look the circuit over for shorts...






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[This message has been edited by Shho13 (edited 09-24-2018).]

Were you able to solve the issue. My '87 GT Auto is doing the same thing suddenly! Pulled the bulbs out of the back and disconnected the wiring harness next to the battery. Still blows. Next step in the investigation is to look at 2 things:
1) Turn signal switch
2) Reverse switch. Where is the reverse switch on automatics?

quote Originally posted by Shho13: Makes sense, the circuit is only receiving power when the ignition switch is in run/bulbtest/start. As long as the "turn hazard switch assembly" isn't the part that is shorting internally, the short wouldn't be any of the blinker lights, or the circuits to them; they are out of the circuit until you physically flip the switch for left, right signal (look at the circuit, you can see how I highlighted the flow of power). It seems you can rule out/in the turn signal switch, the circuitry after it, and the flasher unit by simply removing the flasher. If after you remove the flasher and the fuse still blows, that isolates a whole lot of the circuit; and would mean that the short may be in the "back up lights" section for your hunt for a short, as that is spliced off that circuit before the flasher... If the fuse continues to blow after removing, then you know the short is on the side of the flasher, etc... Here's the diagrams for you to look at to help you along... I highlighted the wire colors, while also guiding the flow of power to you, so that you a basis of what wires you should be focusing on while you look the circuit over for shorts...

quote Originally posted by TikiBird: 2) Reverse switch. Where is the reverse switch on automatics?

Unplug the harness from this switch on your transmission. Any change?


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[This message has been edited by fierosound (edited 10-26-2020).]

Sorry. I'm having trouble picturing where that is on the transmission. Are there any location photos? Been looking online...

quote Originally posted by fierosound: Unplug the harness from this switch on your transmission. Any change?

[This message has been edited by TikiBird (edited 10-27-2020).]

open the deck lid. Stand to the left of engine bay and look down. Is only big electrical part on trans.
If you have cruise, is ~ under the servo and can have a bit harder time to see.

Auto trans N-switch rarely goes bad. Can get loose or out of adjustment but that won't blow fuses but often will cause starting problems.
Carefully Remove White "lock tab" before trying to unlock and remove the plug. Put white part back when done messing w/ the switch.
See my Cave, Neutral Safety Switch

To find shorts blowing fuses...
Take a blown fuse and if needed carefully open the test ports on top so can easy put volt meter or light bulb across the dead fuse.

Turn etc bulbs and sockets only blow a fuse when on.
But switches, relays, and power wires to them can blow a fuse just turning I-key to on or acc depending is light.
Also Bad switches etc can make a bulb be on when should be off is part of why pulling switch plugs can help.

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quote Originally posted by TikiBird: Sorry. I'm having trouble picturing where that is on the transmission. Are there any location photos? Been looking online...

At end of shift cable on transmission.
Shifting PRND21 rotates the shaft the switch is on through the positions.

[This message has been edited by fierosound (edited 10-27-2020).]

I think I see switch based on fierosound's photo above. I can't really reach it due to the cruise control and vacuum cannister in the way.

Yesterday, I pulled all of the tail bulbs (including reverse) and disconnected the wiring harness at the firewall (next to the battery). Wouldn't that have eliminated anything in the engine bay or tail lights? Anyway, the fuse still blew when I turned the car to the "ON" position. Was thinking my next step would be to disconnect the turn signal switch and see if the short goes away. But, I'm out of ideas. Am I on the right path?

Good idea on putting a bulb across an old fuse. I'll build that tonight.

quote Originally posted by theogre: open the deck lid. Stand to the left of engine bay and look down. Is only big electrical part on trans. If you have cruise, is ~ under the servo and can have a bit harder time to see. Auto trans N-switch rarely goes bad. Can get loose or out of adjustment but that won't blow fuses but often will cause starting problems. Carefully Remove White "lock tab" before trying to unlock and remove the plug. Put white part back when done messing w/ the switch. See my Cave, Neutral Safety Switch To find shorts blowing fuses... Take a blown fuse and if needed carefully open the test ports on top so can easy put volt meter or light bulb across the dead fuse. Turn etc bulbs and sockets only blow a fuse when on. But switches, relays, and power wires to them can blow a fuse just turning I-key to on or acc depending is light. Also Bad switches etc can make a bulb be on when should be off is part of why pulling switch plugs can help.

[This message has been edited by TikiBird (edited 10-27-2020).]

Unplug C500 for taillights likely won't help here but doesn't hurt or eat a lot of time.
Because most light wires passing thru C500 are downstream of whatever switches for a GT.

If you had a notchy then there is a Jumper and wiring to "program" the brake lights.
Brake lights is different circuit and fuse so problem isn't that.

Could try unplug large plug to steering column.
Turn switch can be bad or crap got in it but is also different circuit and fuse.

Carefully take HL switch and dimmer out and unplug HL switch. Test fuse-bulb should be Off as I think HL switch is only thing downstream of it.
HL Switch can be bad or can narrow down the problem there.
Careful Jump Orange (Pin A) to Brown (Pin E) on the socket w/ wire then see test fuse bulb.

Park Lights On? Should be but some parts likely dim and maybe too dim or "off..." But Test light at fuse is likely bright.
If the Fuse-bulb is dim too maybe the switch or module is bad. (Switch won't short to ground but short inside could blow the small fuse.)

Keep watching the fuse-bulb for brightness change during this items...
Unplug Dimmer wheel, wheel or trans maybe shorted. See my Cave, Dash Dimmer
Unplug C100 near gas pedal to isolate the entire front. Inducing Gen2 HL module that uses taillight fuse for HL down. See my Cave, Gen 2 HL Motor
Unplug C500 near battery anyway...

Test fuse-bulb Still On, then problem is somewhere in the cabin...
Example Ashtray and lighter bulbs are on same fuse. Lighter and bulb cooks the bulb socket and wires can short to ground but like others need a HL switch to be on.


HL dimmer/beam switch and most of rest of HL parts have known problems but Not on taillight circuit except Gen2 module get down wire when HL and Park lights are Off.
If you think the HL module is "dead..." Very carefully unplug only the big plug. Maybe "dead" but you can kill it just by unplugging it. Solder on the module's board to the plugs are easy to crack so 1 to all pins fail and make module problems.

Here's the recap and solution to my '87 fuse blowing issue.

OK. We got the Fiero out and started digging. As they say, make a plan and STAY WITH THE PLAN.

Got out the schematic and started at the 20A fuse. After the fuse, it splits in two directions: the turn signals and then the reverse light. Following the turn signal side, the turn signal flasher is first. So, we disconnected it and put in a fuse. It didn't blow. So, we're on the right track. We plugged it back in and disconnected C210 under the steering column. That should elminate everything down stream of the turn signal blinker. The fuse blew again! Went back to the schematic. THAT CAN'T BE right; the only thing in the circuit is that blinker... I took the PDF with me to lunch and continued looking at that schematic. Next thing I should check is each of the pins on C210 to make sure they're not hard-grounded. Still bugged me though.

On the way home from lunch, I stopped by and picked up a turn signal blinker -- I knew that wouldn't fix it but it can't hurt either. Got home and swapped out the blinker. NO MORE FUSE BLOWNG! YaY!

The blinker was an aftermarket one and the bracket had squeezed the plastic case and cracked it causing the bracket to short against the input pin. Would have NEVER guessed that to be the cause. So glad it was a simple fix.

Thanks for all the suggestions and ideas. Glad to have a forum where I can ask for help. Guy at Advance Auto Parts asked, "what brand?" when I told him I needed a turn signal flasher for an '87 Fiero. Sheesh. Didn't realize that some self-proclaimed car guys don't know these gems!

quote Originally posted by theogre: Unplug C500 for taillights likely won't help here but doesn't hurt or eat a lot of time. Because most light wires passing thru C500 are downstream of whatever switches for a GT. If you had a notchy then there is a Jumper and wiring to "program" the brake lights. Brake lights is different circuit and fuse so problem isn't that. Could try unplug large plug to steering column. Turn switch can be bad or crap got in it but is also different circuit and fuse. Carefully take HL switch and dimmer out and unplug HL switch. Test fuse-bulb should be Off as I think HL switch is only thing downstream of it. HL Switch can be bad or can narrow down the problem there. Careful Jump Orange (Pin A) to Brown (Pin E) on the socket w/ wire then see test fuse bulb. Park Lights On? Should be but some parts likely dim and maybe too dim or "off..." But Test light at fuse is likely bright. If the Fuse-bulb is dim too maybe the switch or module is bad. (Switch won't short to ground but short inside could blow the small fuse.) Keep watching the fuse-bulb for brightness change during this items... Unplug Dimmer wheel, wheel or trans maybe shorted. See my Cave, Dash Dimmer Unplug C100 near gas pedal to isolate the entire front. Inducing Gen2 HL module that uses taillight fuse for HL down. See my Cave, Gen 2 HL Motor Unplug C500 near battery anyway... Test fuse-bulb Still On, then problem is somewhere in the cabin... Example Ashtray and lighter bulbs are on same fuse. Lighter and bulb cooks the bulb socket and wires can short to ground but like others need a HL switch to be on. HL dimmer/beam switch and most of rest of HL parts have known problems but Not on taillight circuit except Gen2 module get down wire when HL and Park lights are Off. If you think the HL module is "dead..." Very carefully unplug only the big plug. Maybe "dead" but you can kill it just by unplugging it. Solder on the module's board to the plugs are easy to crack so 1 to all pins fail and make module problems.

quote Originally posted by TikiBird: The blinker was an aftermarket one and the bracket had squeezed the plastic case and cracked it causing the bracket to short against the input pin. Would have NEVER guessed that to be the cause. So glad it was a simple fix.

Sorry,,, Don't know why I switch turn for tail fuse but good to find anyway.

Nearly All flasher cans are plastic now w/ most metal shells are NOS parts.
⚠️ Never put any plastic shell cans in most clips made for metal shell cans.
This exact problem has been covered many times like Why would flasher break? https://www.fiero.nl/forum/Forum2/HTML/143961.html

Believe Many OEM metal cans (GM Ford and likely others) were made by Tridon now sold and known as Novita in most countries.
Tridon/Novita EL12 is "new" Electromechanical unit. Might still find old Thermal flashers, Novita no longer makes standard units and Thermal page only point to LL or EL equivalent.
Blazer (FL32) makes an electronic flasher that works too.
Most E-flasher doesn't matter whether is in normal turn or hazard like old thermal flashers.

OE clip is to hold the can and make more sound.
Had a Tridon EL12 but didn't see the clip so crush it in a few months... Didn't blow a fuse but didn't work.
I just push the Blazer unit on top of bottom dash trim and still makes enough noise.