Electrical: involving brake pedal (Page 1/1)
mkoski SEP 03, 08:26 AM
1985 2M4 Fiero

Issue: When putting the turn signal switch down to the left position we get a very faint flash on both sides. When the switch is in the right turn position everything is fine. My son noticed that if he has his foot on the brake then both left and right work fine. in addition, perhaps unrelated if the key is in the on position engine off then each time he depresses the brake pedal the fuel pump primes. If the car is running then depressing the brake does not prime the pump.

104,000 miles on the car unknown if the pump has ever been replaced.

Suggestions appreciated
theogre SEP 03, 12:17 PM
Pull rear lights out to see the bulbs.
Turn on whatever have problems.
Look at bulbs.

Turn lights should only have 1 filament lit.
But likely has both on one side because have one socket or more have iffy grounds.

See my Cave, Sneak Path

Not sure what would cause FP prime issue.
Maybe have other grounds problems. Check G201 and G202.
See my Cave, Wire Service

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 09-03-2020).]

mkoski SEP 04, 08:26 AM
Thanks for the links very informative.

We have pulled the back bumper cover no signs of old repairs or modifications to the rear wiring. The bulb sockets are all original plenty of dried out bulb grease in the plastic pancake ones.

Some additional facts: The hazards work fine both sides all around nice and bright. When activating the turn signal circuit we only have one filament illuminated in each of the bulbs although in the left position it is very faint and both sides glow, exhibiting a very weak flash and low brightness.

This is a 1985 model yet it has a third brake light that has clearly been added dealer or a PO the wiring heads into the bulkhead we will pull the console tomorrow and see what we see behind it.
theogre SEP 04, 02:56 PM
Hazard has all bulbs to load it and often works when turn lights won't.

Dim bulb is just as bad and likely still a socket/ground problem when right side are bright.
Only the Bright filament sound be on for brake/turn. If dim side is on w/ or w/o bright side, has a ground problem.
Bright side might not lite can see easy depending on exact bulb # and brand w/ ground problems.

Bulb grease is very think and looks "bad" to many. Ignore that.

See my Cave, Lighbulbs
Do you have new bulbs? Look at sides of bases for scratches etc. Nothing or very little can weak grounds... "Pinch" the ground ears just a tiny bit can be all you need. But Too much pinch and bulbs can get damage and hard to install or remove.

old bulbs can get damage over time. replace them. NAPA and other have 10 pack often cost far less then 2 pack at any place.

high mount brake is nearly all DIY install. You may need to pull many things to find exactly what they did.
mkoski SEP 05, 10:02 PM
Issue Resolved

Aftermarket third brake light has been removed looks like it had been in there for a very long time the mold that made the dot lenses was 1984.

The install was neat and well run but after all the years the yellow wire at the bulkhead was just about separated into two pieces. A bit of soldering and some heat shrink and all is in order.
theogre SEP 06, 01:07 AM
Nice.

Very likely DIY or 3rd party installed part. Dealers can install some options but likely not this.
Make sure you find all wiring changes... 85 and earlier would need HM Brake hot wired all the way to Brake Pedal switch etc under the dash to work right. Ground can be anywhere.

Side note:
DOT dates isn't date made but more like year of first made and tested for "DOT Approval."
Example: Every notch back Fiero shows 84 on Taillights assemblies.
Read bottom of light bulb page if didn't read already.
When (Not If) a mold wears out, replacement molds has same DOT string etc to make same part as "Approve by DOT."

True that 86 Model Year required all Cars had HM brake light. (Only years later trucks, vans including mini van, etc got them.)
Plus when FMVSS rules changes final MY for new/change rule can change depending on many things including car makers fighting NHTSA.
At minimum likely GM started in 84 to HM brake parts for Fiero and other just to get ready for 86 cars built in 85.
Remember Model Year is not = to Calendar Year.
Brands started selling 86 vehicles ~ 4th Quarter of 85. Some brands/models even before that... Most Factories had to make them months before that to ship to dealers to sell.

[This message has been edited by theogre (edited 09-06-2020).]

mkoski SEP 06, 08:46 PM
Here is the offending part.
theogre SEP 06, 11:21 PM
That's not a GM HM brake light... Many people added GM one to 85 and older and had to wire as above.

Is an Aftermarket unit sold at many retail stores not just auto parts and small box has 2 wires (green in this case) run to both side taillight wires so idea is you don't have to wire to the dash.
Problem is small box have problem then very likely taillights also has problems.

Many companies made these "kits" during late 80's to early 90's. Even now can still find them.

Was this mounted on the bottom of rear glass? Look like because wiring.
Works but not same as 86+ HM light. For 1... Unlike OE light, this light may have delay to turn on because of small box.
Plus many Fiero has luggage rack so GM install them top of glass so small things on deck and GT Wing won't block it.

Part of the idea HM Brake is one behind you hopefully is not only to see. If you hit the brakes, often 2 or more drivers directly behind could see this w/ HM brake.
This was before you have 1/2 or more people driving SUV etc and worse w/ Limo Tint Glass as OE for all windows except front sides and windshield. Now you hope morons behind you aren't watching YT etc while they tailgate you.