E-30 electrical-please help!

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.

Your battery cable from the battery to the junction box is my guess. Sounds like there is a high resistance in that cable - I would guess a poor connection at one end or the other. I would measure the reistance of the battery cable and perform a visual inspection of it to look for problems.

i will check that for sure. i have looked it over and couldnt find any tears in the insulation but the end connecting to the battery does look a little worn. i have a spare cable i may try to drape outside the car and hook up at both ends to test it again. any other suggestions?

so i cut off the battery end of the cable last night and put on a new termination piece and everything works! the end i cut off still looks fine so who knows what is going on in there. but thanks for the great call! who knew that could make such a big difference! mike

Mike, Glad you got it solved!

you mentioned 12.xx volts. 12.6 implies 100% charge, 12.4= 75% and so on. not alot of people realize it but the .xx makes a difference

GRM board is Magic!!! Someone should send TJ a prize!

yep. you guys rock!

the sad part is a similar message is still sitting.... responseless..... on the E30 tech forum. maybe i offended them by removing the oem fusebox.

ok so i got the electrical system buttoned up and test fired it this weekend. after failing to insert fuses the first time and failing to connect the bulkhead connector the second time the eneghine fired up f3 seconds into the stsrter turning. woo hooo! now there is only one other problem. it doesnt want to turn off! the main switch runs the coil wire, the fuel pump, the main relay7, and the motronic power the same way the key used to, but when i flipped the switch off, the engine kept going. i actually had to stall it by pulling vacuum lines! any e30 guys out there have any idea what is going on here? is there a back door for main power from the alternator or something? when i originally took the car apart there were 2 red wires attached to the main power line from the battery junction block to the underside of the fuse panel. i have these two wires going directly to the battery junction block now, is it possible these wires are taking power from the alternator and keeping the car running? is it possible that the fuel pump had stopped and residual pressure in the lines left it running for another 30 seconds? any ideas would be appreciated!

ok so i got the electrical system buttoned up and test fired it this weekend. after failing to insert fuses the first time and failing to connect the bulkhead connector the second time the eneghine fired up f3 seconds into the stsrter turning. woo hooo! now there is only one other problem. it doesnt want to turn off! the main switch runs the coil wire, the fuel pump, the main relay7, and the motronic power the same way the key used to, but when i flipped the switch off, the engine kept going. i actually had to stall it by pulling vacuum lines! any e30 guys out there have any idea what is going on here? is there a back door for main power from the alternator or something? when i originally took the car apart there were 2 red wires attached to the main power line from the battery junction block to the underside of the fuse panel. i have these two wires going directly to the battery junction block now, is it possible these wires are taking power from the alternator and keeping the car running? is it possible that the fuel pump had stopped and residual pressure in the lines left it running for another 30 seconds? any ideas would be appreciated!

update! i found the issue and the car is up and running again! drove it up to the gas station to get it filled up and it runs just fine. maybe wiring isnt the devils tool like i thought!

for those that are curious about why it kept running, it seems that the line to the o2 sensor relay from the fuse box was not there to switch the relay on like the schematic suggested, but it was actually the electrical feed from the relay back to the box. so it was backfeeding the fuse box once it was running. doh!