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ok so 1986 528e stock automatic. I pulled the original intank fuel sender assembly out as i believed to be non-operational. I know it's not really necessary for these cars, as the main external pump does the work, the internal is just for lower fuel levels to ensure fuel gets to the main pump when down around a 1/4 tank or so, I think.

But becasue i like to have things working properly though, i replaced the original with a herko fuel sender assumbly, didn't want to pay for the BMW oem part and heard positive things about this replacement. When going to start and to test it out, immediately blew fuse #1 and car wouldn't turn over. replaced fuse and tried again with same result making sure fuse was not loose, etc. replaced the fuse again and unplugged the intank sender connector and she starts and runs as normal. So clearly there's an electrical issue or something with the sender assembly.

I put a multimeter on the fuel sender connector wire contacts and got ~13v or so across that so tells me i'm getting good voltage via the connector wire. looking at the wiring diagram the sender assembly gets power from the main pump and both are grounded via the same splice (S318) same ground connector (G301) under the read seat. So given that the main fuel pump works correctly when the intank assembly is disconnected, this tells me that the ground is good otherwise the main pump wouldn't work correctly. I don't think fuel relay is at issue since the car starts and runs fine off the main pump.

So my next step is to check the splice connection and also check/clean the ground connector under the rear seat just to ensure the connection is good.

Is there anything else i can check to determine why the #1 fuse is blowing when i reconnect the in-tank fuel sender? I could try a different brand of fuse , but feel that's a longshot since i'm using the same brand in most of other fuse slots with no issues. but worth a try i guess.

Any possibility that the positive and negative have been connected backwards when assembling the new pump???

That or the positive was touching the metal of the pump or the support somewhere

Aldo525 wrote: Jul 04, 2024 12:20 PM Any possibility that the positive and negative have been connected backwards when assembling the new pump???

That or the positive was touching the metal of the pump or the support somewhere

My thoughts too.

I would double check how members cek and or Davintosh did their own electrical wiring around the inner tank pump stalk. I followed the same and had no problems.

Lucky for you she’s only burning fuses.

A lifetime ago, unknowingly connected the wires that came from my Rallye DVO fuel gauge and took my car to proudly fill her up. 25 ft after leaving the gas station the fuel heated enough that my tank exploded behind me. It was a French Simca 1204 race car and my bucket seat protected me from burning, just another for the unforgettable car mistake experiences.

Yes I was young then, and to this day stupid to a point, so that’s why I double check everything I do. You’d be wise too. Good luck!

On the Herko pump, the positive wire is not routed properly down thru the assembly. This lends to the red wire getting caught and punctured once you snug everything down. Happened to me on my 533, even after I saw the routing issue.

Your car's wiring is likely fine, just like it was before the new pump. The variable is the new pump.

You probably need to pull that pump to check the positive wire for damage, however small. Either that or your new pump has another break/chafing in wiring somewhere.

Good luck, any questions lmk.

Aldo525 wrote: Jul 04, 2024 12:20 PM Any possibility that the positive and negative have been connected backwards when assembling the new pump???

That or the positive was touching the metal of the pump or the support somewhereconnections game

At first I thought so too, but then I thought maybe the anode was broken.