Informational post, did a search but did not find this scenario.

98 ML 320 intermittant cranks, no start or intermittant engine dies.

check fuel pressure, ok.

Check for ignition spark, none.

Crank sensor replacement (usual fix) no help.

Scope and pin testing, crank, cam sensors, coil resistance, wiring, all WIS ignition tests passed but yet no spark.

Applied 12 volts directly to coils (middle wire of coil connector) and engine
fired instantly. Jumped to coil fuse f26 same result.

Continued to back test wiring,cir15 terminal of ignition switch, burned contact, would flow enough voltage to pass all the BOOK TESTS but not enough amperage to supply the coils.

Replaced switch, ($15) available separate, pops out of the steering lock.

Replacing the $15 ignition switch restored the amperage capacity of the circuit. The engine started and has continued to run.


BTW, this was a former RAP vehicle,110000 miles and many ,many ignition cycles


This information has been provided by a clown who works in a stealership

__________________
Paul