If your fan worked before you upgraded your new fan isn't grounded. But you should still check the wire feeding the fan before you go tearing it apart.
If you don't have a test light or meter try like you said and run a wire directly to the fan to see if that works. If not then it's a bad ground. If it does work it's the switch.
yeah the fan uses the firewall as a ground....so if it doesnt have good contact for a ground its going to be worthless. I'd go check the ground by touching a jump wire from the portion sticking out of the firewall in the engine bay to a solid ground and see if it works.
1985 CJ7 Project Phase One : 5.3L Vortec/4L60E, Moser axles for AMC20, Twin Stick'd Dana300 - Completed Phase Two: Bedliner, Rollcage, Seats, BESRK Rear Bumper w/ tire swing, Soft Top, and a few other goodies - Mostly Complete Phase Three: Waggy 44 front, Scout D44 Rear, 4.56's, ARB's (F/R) SOA with YJ Springs, 35x12.50x15 BFG MT - Not Even Close to beginning
Also a mostly rust-free 1970 Scout 800A That I'll get to start working on someday...
Chrome won't get you home...BUT Rattle Can Black may just get you back"
Might be easier to add a ground wire/strap.
Use a self tapping screw on the outer housing after you sand off a clean spot. Put some solid #10 wire under it, and then to ground elsewhere. If it works, I'd go with it.
'85 CJ7, BDS 4" lift, 1" Body lift, 33x12.5, Shrockworks Sliders, 304 V8 with RV cam., T-176, D300, Dana 30, AMC 20. 1986 CJ10-A SD-33 Diesel/727/np208 1971 800B with 345/T-19
06' TJ Rubicon, 4" R.C. springs, BFG/AT 35s M.C. 6" fenders, rockers and surrounds, Currie front & rear adj. tracbars, tattons DC rear shaft, adj. upper - lower CA's. Bilstein 5100's YJ Buggy Build Current project. Stroker/FI ?
1990 MJ Comanche 4.0L AX15/np231
I had to cut the fire wall like most guys that did mod, problem is my hole was enormous. After I cut it, I was like damn! I guess I miss marked it when I drew the circle.
So I thought I would use some cork gasket and some RTV and seal it up. My rig is more function than looks.
Think all my RTV has somehow killed the ground?
NO. It does not ground there. In fact, it does not ground directly to the firewall. The heater motor bolts to the blower motor/heater core housing which bolts to the firewall (those four studs going into the engine bay). You should be able to put a ground wire on any of those bolts to keep from making another screw hole.