Troubleshooting Tips for the Headlamp Module

Please note: the photocell latchup only works when the engine is running and the alternator is properly working: 13.8 VDC.

In the event that you have made all the required connections to the module and, it does not work as expected, here is how to troubleshoot the installation and the hardware from us.

First, make certain that you have a good ground connection at the module: test the resistance from the terminal #7 (gnd) to the vehicle's ground (like the engine block, or something you know is ground). The reading should be zero.

Verify that term #1 (12V) has 12 volts present at all times. Check that term #8 has 12 volts present when the ignition is switched on.

Next, check just the photocell: you want to measure the resistance of just the cell, disconnected from the module. Depending on the specific cell, you should see about 2.9 K ohms across the leads when the the cell has light on it, and about 85 K ohms when dark (another cell we are using shows 1.2 K light and 35 K when dark). The point is that there should be about at least a 30 K ohms change in the resistance of the cell, from light to dark. If you don't see that, then the cell itself is defective in some way.

Now reconnect the photo cell to the module. You should check the voltage at cell terminal # 5 (the first term for the cell). It should be the same voltage that you see at terminal #8 (ignition). The negative side of your meter should be at ground. Cell terminal #2 (the 6th screw terminal) should be about 9.7 volts, with the ignition "on", and the cell has light on it. This terminal should drop to about 1.6 volts when the photocell goes dark.

If the photocell checks good, and you do not get the results, as above, the module is defective, and we will, of course, replace it.