300SDL
I had an odd situation where my tach went dead at the same time as my "antilock" idiot light went on. Tach stayed dead and warning light stayed on after restarts. Reading some forum posts, it smelled like a bad OVP relay. So I swapped the OVP out with a good one I had lying around, and...FIXED. Every now and then there ARE easy successes.

Thanks to all the brave pioneers who skinned their knuckles before me.

I had a similar issue on my 87. I replaced the fuse on the OVP and that resolved it. I did decide to replace the OVP as it was old.

Yes, indeed, one must check the fuse first, rather than just junking the thing. I did, but I can't prove it.