Blown fuse

Marco,

The only time the airframe ground should be connected to the engine ground is when either the start power switch or the emergency battery switch is turned on.  According to the manual, the only thing fuse F15 does is supply power to the warning light. This makes me wonder if a short in the wiring from the HIC connector to warning light B would cause both problems. Because the lane warning lights are supplied by the engine side power, it seems likely that shorting that wiring to airframe might also short the engine and airframe grounds together.  I have no wiring diagrams to support this, but it seems reasonable.  

There was one other post on this site regarding this same fuse blowing, and in that case they did find a short in the warning light wiring to the airframe.  

thank you Jeff B

I check the wiring as you said but I didn't find any problems except starter relay body was grounded to aircraft ground. I disconnected but no changed. when rpm increase to about 3000 , two warning lights blinking ,(( BUDS error is Generator in fail safe mode) in this rpm ECU wants to switch from Generator B to A but it seems that there is no power on regulator A to power the ECU , I check GEN. A&B and changed regulator A&B (step by step ) but no changed ,

when I changed fuse box  the problem SOLVED , I check all the component in side the Fusebox ( 3 Relays, resistors, capacitors , diodes ….) but I didn't find the reason, 

when I install this fuse box the problem come back

Marco,

It’s ok if the starter relay body is grounded to the airframe as long as the coil terminals (A1 and A2) are isolated from the body and connected to EMS power. It seems you have isolated the problem to the fusebox, but it would be nice to know more about what has failed.

I noticed that at the same time you are getting the “Generator Select in Failsafe” fault, you also have several other faults including “Generator Select Switch Short”.  I have not seen this before, but the generator select switch is internal to the fusebox and fully automatic, so that may be the problem.  You may simply need to replace the fusebox.  Maybe someone who is more familiar with these codes will also post.  I’m curious about the following:

1. Are you using your old voltage regulators with the new fusebox or are they also new with the new fusebox?

2. With the OLD fusebox installed, are the A and B grounds still reading continuity between them, and if so, does that change when you install the NEW fusebox?

3. With the NEW fusebox installed, is the battery voltage showing a charge (>13.5 volts)? I’m just wondering if alternator B is making power once the switchover happens.