96 F53 chassis turn signal 4 way & brake lights not working

enblethen wrote:
There could be two fuses. One control and one power.
The turn signals and the four ways should be on two different circuits as the four ways work with ignition off and the turn signals work with ignition on.

That's not completely true. The 4 ways work with the ignition on or off on the OPs chassis.
If all else fails, the multi function switch on older F53 has been known to fail. It's an easy change and is available on Rock Auto

Richard
95 F53