this is kind of long because i am so confused that i wanted to put all that i know out there so hopefully someone will see something i missed. please shout out anything you think i should check because i am stumped!
i am trying to fix the wiring in an E-30 that suddenly died last fall. the original diagnosis form some e-30 fans was that the central locking, unloader relay, or si board system was shorting the remaining system. since i couldn't get power to stay hot to the fuse box long enough to do any real diagnosis, i went with that diagnosis and started to work on ridding myself of those unnecessary systems.
to do this i got a universal fuse box with 3 banks of 4 circuits and set each bank up on a separate 50 amp switch. the original fuse box was removed and power leads were taken from the junction box on the firewall, through the 3 main switches, and into the fuse box.
i tested all of the leads to the fuse box and i get a steady 12.XX volts at each head in to the switches, and when the switches are turned on, i get the same voltage to the fuse box head ins. that is, until i put a load on the fuse box! once a load is activated the voltage drops everywhere in the system to a few hundred millivolts! it doesn't mater what load i put on it. window motor to parking light does the exact same thing and it is instantaneous. no fuses blow, and even when i remove all of the fuses but the circuit i am activating the same thing happens.
i tested one of the simple circuits (parking lights) by just hooking up the battery positive lead to the wire from the protected side of the fuse box to the accessory and the circuit seems to work fine. it is just when it runs through the fuse box that it doesn't work.
i thought at first that it may be the battery ground, but again i checked this by hooking up a positive lead directly to the battery and then a negative lead directly from the nut holding my negative terminal to the chassis and ran that through a parking light and it worked.
any ideas? it seems like all of this is telling me my fuse box is bad, but it seems highly unlikely that two fuse boxes in a row were bad (the original oem unit and the new one. and it seems even more unlikely that all three separate fuse banks would have the exact same problem.
