1988 GT, 3.4, 4T60

Still having issue with driver side headlight not popping up. Replaced slotted plastic big gear with Rodney's steel. Replaced motor white plugs. Used enclosed grease. Headlight popped up fine for a few times, then sometimes, now never. Passenger side fine.

Paid way too much for a "new" HCM. Didn't work at all. Put old HCM back in. At least right side headlight pops up all the time.

Saw this video: https://youtu.be/nafNZ6vx-V4 Looks promising, but can't find a source for the transparent cased relay.

So . . any ideas for source for a new 12 volt relay to install in original TCM?

Or, any reliable source for a new HCM?

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John W. Tilford

This is as close as I could find to the video. Same relay, just 12 volts only and 3amp instead of 5. Whatever route you go, you'll need to make sure it is "through hole" mount like the one I linked.
https://www.digikey.com/en/...y/MY4-02-DC12/283171

Here's the pinout

[This message has been edited by IMSA GT (edited 03-29-2025).]

To Me, don't attempt to replace the relay IF you don't have the proper soldering tools and skills.

GM still offers the OEM part number 16523917...{hold on your butt}

Eckler's Corvette # 25-376108-1 is cheaper

FYI - Fiero Headlight System Troubleshooting by Oliver Scholz {'84 thru '88}
http://www.fieros.de/en/articles/headlight.html

Also - Headlights: Left will go up, neither will go down by Cliff Pennock
https://www.fiero.nl/forum/...130314-2-095675.html

EDIT - I finally found *This* thread from last year....
Headlight Door Control Module by gregr75

quote Cliff Pennock: And a second word of warning, some are "refurbished" by replacing defective MOSFETs.

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 03-29-2025).]

You can buy a brand new headlight control module. Just a simple plug and play solution.
New Headlight Control Module

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Just ordered the Eckler's EK-25-376108-1. This evening (29 March - Vietnam Veterans Day ) they had three "open box" headlight control modules. Two "good" and one "very good". The very good was $81 + reasonable shipping and sales tax = $97.32. The same EK number not open box was $270.

Certainly worth a try!

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John W. Tilford

[This message has been edited by John W. Tilford (edited 03-29-2025).]

If the new relay doesn't fix the problem, try replacing the headlight switch. That was the problem on one of mine. Each motor has it's own switch circuit.

[This message has been edited by fierofool (edited 03-30-2025).]