Most of the electronic modules on these older cars come apart with a few screws, or a little careful prying.

I'm not sure how the fuse-less relay works, but it shouldn't be too difficult to at least get in to take a look.

When it was sticking engaged, I reworked the glowplug relay on my 300sd, just a matter of filing the points that were sticking.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...