Frankenbike charging/tach issues

[Rasputin]

I recently bought an 81LH and it has a 79SF engine in it. I got the motor running by replacing the 4RO with a 2H7 TCI unit and chopping a 1/4 inch of of one plug wire. Now it is running fairly well, still needs colortune and synch.

The thing is the tach is not working and I am going to check the charging system out today. I am wondering if there are any obvious things I should be looking for with the motor change. Maybe things like the rect/reg, or, wiring harness changes that may be different. Any input will be appreciated as I dont want to chase my tail looking at things if there is something really simple. Thanks everyone.

[TopCatGr58]

Hey Rasputin,

Okay, 81LH FRAME with 79SF engine, swapped out 4RO TCI with 2H7 to get running. 81LH ignition coils are at 2.5 ohms, wiring does not have ballast resistor, but with those higher ohm coils, you don't need a BR even with the
2H7 TCI...just an FYI.

As for the charging system, it's still got XS components, not brushed ALT like the XJ, so the wiring is the same for it or a 78E. I would look/check the three big plugs behind the fuseblock plate for signs of corrosion, melting, etc.
Then check the Reg/Rect's housing to frame connections, the bolts, the several wires connected via the mounting screw, clean all.

Check for magnetism on ALT cover with feeler gauge with key on. After cleaning all connectors, run, retest charging, if still not above 12 volts, then put a tap to the green wire that's with the brown/green set and run to ground, if voltage goes up to 14.5 spec or so, then REG/RECT is suspect. IF voltage stays near 12 volts then field coil/stator are suspect.
T.C.

[Rasputin]

Thanks TC. I found all the tests searching on here and will try to do them today time permitting. I had no idea about the ballast resistor part so glad that it will work as is. I was pretty sure the parts were the same on all XS's but I would have spent days on it if I was wrong. Now hopefully off to the garage and find the problem. I have a 78E that I can use for parts if I need any.