Headlight flash acts as a momentary switch on the high-beam circuit, not the low-beam.

Not sure if Gen1s use the same combination stalk cluster as Gen2s, but if so, I've got a similar issue where I need to hold the stalk pulled slightly towards me, but not enough to engage the flash, for the headlights to work at all. Pulled the combo cluster and disassembled enough to find the inward end of the stalk had a chunk broken out where it holds a spring in the end. That spring acts on a BB which engages the detents for high-beam, low-beam, and flash positions. With the chunk broken out, that spring has a bit of slop to it, leaving the stalk resting in-between low- and high-beam positions, so I have to hold it just-so to keep the low-beams on at all.

Driving around like that is a PITA of course, been meaning to take the cluster out again and see if I could attach a narrow metal strip to replace the missing plastic chunk and re-center the spring properly. I could just replace the cluster with one of those cheap Chinese ones listed for a Mitsubishi L200 on AliExpress, but this cluster is already one of those, and this failure occurred only a few months after I bought and installed it, so buying another might just be throwing good money after bad.