Just purchased a 90 8100 international L10. Have a few questions

Hello, I am new to the forum. I just purchased a 1990 international 8100 with L10 Cummins. I have searched everywhere I can think of for any type of wiring diagram for the truck and can't find anything. I am having a few electrical issues. The truck is in fairly good shape but needs a little tlc. I am having some issues with the lights and blinkers. The blinker switch shows no activity on the dash or the front or rear signal lights. Nor do the flashers come on. I have no idea the positions of the fuses in the panel and can not find anything on the 8100's anywhere. I have some switches that needs to be replaced and can't find anywhere that shoes what other models are compatible with the 8100 because I can't find anything in the 8100. Any help would be greatly appreciated.
Thank you

 

Thank you Heavyd. I have seen service manuals on eBay and dang there a pretty penny! But if I have to I have to I guess. Thanks again!

 

Thank you spsauerland

 

Where is the best place to buy parts such as interior switches like head light switch, turn signal, hazard and wiper control? That is a hard one to look up as well. It may help if I knew what all series and years interchanged with my 90 8100. Thanks for all the replies. Keep them coming