Many approaches, but what I did when faced with similar problem, I hooked up a mechanical gauge off(old Stewart- Warner I had) an engine block oil access port. I left it in the engine bay temporarily where I could keep an eye on it and not have to go thought bother of running lines through the firewall. I used a remote starter switch to fire it up and discovered my electric dash board gauge was not working properly.
A word of caution here, I knew I had oil pressure but was concerned because the original guage read too low even when cold and with 20-50 oil..the opposite of your problem but an approach to consider after you insure the oil filter and by-pass are up to snuff!