1991 D250 turn signal issue.

My newly acquired D250 truck has no rear turn signals. Fronts work as normal. I don't want to probe holes in the wires to test for power in the main harness coming out of the firewall. Is there a good way to test the multi-function switch? Any help would be appreciated.

Do you have brake lights?

No. No power for brake lights either.

Just slide a paper clip or cotter pin into the connector along side the wire and test for power.