Lincoln ranger 8 onan 16 all my outputs 110/220 work perfect but will not weld

I replaced a diode that the wire had came lose from but that really did not help the way it welds. I can hook another welder I have up to it and burn a rod through a 1/4 in piece of steel so the generator part is working fine.

Step 1 is to obtain the service manual for your welder, usually available on the web somewhere. If that does not answer your question, then post a link to it when you ask again and you might get someone who understands welding machines to help.

When the same thing happened to my Ranger 250 (closely related but not quite the same) it was fortunately under warrantee. Factory service center swapped every board they had in stock, no luck, and then ordered in and swapped the main board. Out of warrantee that would be a repair you might not be able to justify the cost of...

No actual idea what failed, of course, as no component level diagnosis was done (and would be difficult with the boards conformally coated.)