I have a 1997 RR SE P38 with 142k miles; I have some electrical problems, which have challenged most RR mechanics i know. it started with SRS light coming on intermittently, then ABS light comes on when i start the truck and goes out after a minute or two when driving. Left the truck on my drive way one weekend and the following week it start but the shifter will not come out of park, failure massages on the dash shows,” fuse 6,7and 17 on the BECM failed, gear box failed, and check engine light is on. Also some times will show that front windows and sunroof not set even when there are all up.
I thought it was the BECM and i went got another used replaced relays (i have the electrical drawing for this truck and am a Avionics technician) so i understand schematics very well. After all this i found out by testing the relays that all were ok, diode caps, transistor and fuses too.
Ok to shorten my story, i found that i can jump power to fuse 6 from other fuses and am able to drive. The main problem is there is no power going to the brake switch. I have replaced the switch, checked and cleaned the grounds; check accumulator and pump check power to the relays under the hood check the battery, brake fluid and sensor, i have replaced the front brake pads and all looks good. The wiring is not very clear from the main fuse to the brake switch to the BECM, seem like something is stopping the BECM from putting out power to those system tied to fuse 6,7, &17.Am almost 95% sure its not the BECM some mechanics think its the wiring broken some where but i can't find it, Please help thanks

 

My opinion is it is an alternator problem (these vehicles do very strange things when the alternator is gone/going). Sounds like you replaced the fuse box but, if not open it up and take a look inside. They like to melt down internally and look normal on the outside. Does the ABS light go out after you exceed 5mph? It is normal for the abs light to light up and then go away after you start moving. Good luck!

 

I have not checked the alternator but i will,it still starts ok but dose drain the battery after i leave it parked for a day.I did check the fuse box inside cleaned with contact cleaner and ohmed the contacts and grounds.Tha ABS flashes with audio when i start and when i put a jump to fuse 6 to power it,the ABS stays solid on but i can shift to drive.The main thing now is the ABS fault and the gear box fault which is caused by no power on fuse 6,7&17 of the BECM and i think its because the is no power going to the break switch and am not sure what is causing it.I appreciate any help,thanks

 

Sounds like a combination of problems. The draining of the battery sounds like a bad diode pack in the alternator but the other problems sound like grounding issues. I woud verify that the alternator is working properly and then check as is loosen and retighten each ground on the RR, then check out the main fuse box and go through all the connections. Most people overlook the fact that it takes a complete patch for current flow not just the hot side.

 

I will sure check the alternator diode pack, grounds and fuse box and get back with the results very soon, thanks stay tuned please

 

I am checking the alternator, and i found it has 2 wires the big red positive and the small black wire, which am assuming is the ground. This black wire is open and its not reading ground, can some one confirm this is ground wire for me so i can go ahead ground it, i can't find where its goes to because of the wire bundles, but its causing my battery to drain out over night, thanks

 

have you downloaded the rave service manual for the P38 rr? Here it is and it will explain how the whole electrical system works. http://green-oval.com/joomla/index.p...d=13&Itemid=29

 

If it is like my 1996 4.0 SE, then the second wire is not a ground. It is +12 volts only when the alternator is turning.