Tach and Fuel gauge problems on 93 300D (124)

[oldblue85]

I just purchased a 93 300d 2.5 turbo and I am experiencing an intermitent problem with the Tach and Fuel Guages. Ocassionally the fuel guage will swing wildly from 'e' to 'f' and the tach will stop working. It appears that this occurs at the same time on both guages. After a period of time both guages will begin to work correctly. All other guages work Ok. Is there a common circuit between the fuel guage and tach? I've read that a good diesel additive might take care of the problem with the fuel guage. Is that the likely culpit. Is it likely the the tach issue is being caused by the "trash can" rpm sensor under the hood?

Thanks for taking the time to read this and any advice you can offer.