Headlight Control Module Fix? - Third Generation F-Body Message Boards

ternandes · 09-22-2009, 07:27 AM

OK, guys... we have an 87 Firebird and and 88 GTA, both of which use the headlight control module that mounts on the firewall next to the brake booster.

The 87 was the initial project. When we had difficulty with the headlights, and traced it to the module, we found that rapping the module would get it to work, but only temporarily. Sooner or later, it would stop working properly. So, we swapped in the module from the 88, and all problems disappeared.

I am now researching parts and other info for restoring the 88, and I learned to my horror that it is nearly impossible to find this part new, and if you can find it, it is a $300 part. Now it is possible to obtain the module as a used part; there's a place that refurbishes them and sells them for $60.

In addition to the risks associated with buying such a part used, I am sure that supply will dry up eventually... that's why I decided to try and fabricate a replacement. After looking at the repair manual schematic, I reasoned that it would likely be simple enough to just build something with the necessary relay(s) to replace the OEM part. I'm sure that some would regard this as a 'hack job', and it would not please the judges at car shows... AND...

Something in the schematic bothered me -- while it clearly showed the relay(s), it did not specify what else was in there. It just shows a block with connections to it.

After research, I learned that this particular system uses 2-wire motors, and the module performs the following tasks:

when the headlight switch is turned on, it applies power to the headlight motors, to make them pop the headlights up
when the headlights reach the end of their travel, the module senses increased current demand because the motors are pushing against the 'stops'
At this point, the module removes power from the motors to keep them from overloading
when the light switch is turned off, the polarity of the motors is reversed and applied, and the headlights are retracted
again, at the end of travel, power is removed when resistance to the motors is sensed

SO, I decided to open up the defective module, as it seemed to be a matter of prying with a screwdriver. The case opened with little difficulty. Inside, I found a circuit board, with chips, diodes, and a couple of transistors. This is evidently the logic circuitry that does all the decision making. There is a single relay in the center of the board, and this is the part that reverses polarity, on command from the board.

There is some heat warpage on the clear plastic cover on the relay. Owing to the fact that tapping the module with a screwdriver handle would get things working, I am assuming that the relay, which is the only moving part, is what has failed here.

The relay is made by Omron, and the part # is MY4-02-US 12VDC. I have only found it at one source: California Radios Plus, $13 plus $7 shipping. There is a replacement part made by Omron that is sold by many, including Mouser Electronics, and it is cheaper than the original part. The problem is that it has flat terminals on it, and the original has pins that are soldered to the circuit board. I assume that if you were a patient sort, you could modify the relay and/or the board to accept the replacement, which is only $6 plus shipping. The reason I mention this is because it appears that eventually Cal Radios will likely run out of their stock, which I assume they cannot replenish.

I am going to play with this a little, and if I can repair the module successfully, I will let you all know.

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ternandes · 11-15-2009, 01:28 PM

UPDATE -- sometimes procrastination pays off. Just for grins, I plugged the module into the GTA just to see for myself that the relay was not right.

In fact, the relay seemed to be OK... yet the lights only worked intermittently. I played with the loose board while turning the lights on and off, and noticed that the relay sometimes clicked when I moved the board.

A close inspection finally revealed the problem: There are two clusters of pins, one for each of the two wiring harness connectors. Since my vision is not what it used to be, even with my glasses, I had missed noticing that some of the pins had broken solder joints. Once I took a close look, I could see cracks when I wiggled the pins.

It looked as if they were 'cold' solder joints, with barely enough solder. I took a soldering iron and some rosin core solder to them, and now the module works fine.

I think I remember seeing somewhere where somebody 'reconditions' the modules -- and this guy mentioned cold solder joints.

In any case, my module is working like new. Anyone wanting help with this, give me a holler. It beats the hell out of $300 for a new one, or $65 for a used one.

Stephen · 11-15-2009, 02:22 PM

I swapped my 87 GTA one out for a 89 GTA one, for the same reason. Sometimes worked, sometimes didn't, or a tap on the box would "fix" it.

I never did anything with the 87 box & now my 89 box has started doing the same thing. I usually look for speed bumps or pacement dips/transitions, to avoid having to get out of the car, to do the tap thing.

I'll try resoldering my 89 one, as I have no idea where my 87 one has walked off to. Been a few years since I did the swap between them.

HCR13 · 11-15-2009, 04:24 PM

yeah, mine had died a while back, turns out one of the wires inside the relay inside the module had burned off, and was loose, so over bumps on the road it would work and sometimes it wouldn't. I opened up the module and fixed (soldered) the problem and it has been working great ever since!