I have another question for you Mr. Punch...
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Is your oil pressure sender for you gauge a two wire (signal and ground) or single wire (signal) sender?
I finally got my vise mounted to my bench and was going to drill and tap a hole for a ground wire on the coolant hose adaptor and got to thinking about the oil filter adaptor. There is no ground lug on that either and I have a single wire sender. So... it will get its path to ground through the adaptor. I just don't see how it will provide a good ground for the sender with the big square cut o-ring and all the powder coating. I used the sandwich adaptor with a mechanical gauge and one with a two wire sender and they worked great. I'm just not sure it's going to work as well for single wire oil pressure sender.