rt61

Hi, I've got an '82 911SC. I'm replacing the fuel pump and have concerns that the wiring was not set up properly from before I took the old unit out (FYI - the prior owner had the original unit replaced about 20 years ago).

Yes, I know the two leads to the fuel pump have different size nuts (8mm with the -, and 6mm on the +). The wires on the car are Black (which has continuity to Ground) and Tan (which I am assuming would be the 12v supply when the fuel pump relay is shorted) - see attached picture

What is confounding me is that the Black ground wire (which I would normally assume is the -) has the smaller connector that only fits the 6mm + post. Am I getting the convention wrong?

I checked the old Bosch unit and it is marked with a + at the 6mm post, and - at the 8mm post - see attached picture. I've also included a picture of the new unit that is connected to the fuel line.

Since this is just a motor, couldn't the pump have operated reversed polarity and worked (albeit poorly)?

Your experience and guidance are appreciated.
Rick

2specs

I had the same issue. I changed my fuel pump last summer and was boggled by the same thing. Black-positive didn't make any sense. In the process of removing the old fuel pump the black WAS connected to the positive. I had to pick up new washers from the dealer and asked if this was right. He had gone back and asked one of the mechanics and came back with the reply that I make my connections exactly the same way I took them off. When I asked what would happen if they were reversed he said that it would be very bad. Lol...Would the thing blow up? Seize? Start a fire? He just said not to do it. Hook it up the same way, so I did and it worked.

psychoideas

I have a 76 and my + is black and all my - in the whole car are brown.

My current flow diagram lists all earths as brown.

Hope this helps.

ivangene

I changed mine about 2 weeks ago....nice little job, easy and rewarding

in my case I wondered about the wires prior to going in and asked my master tech. He said, you cant mix em up... one is bigger than the other, I never looked twice after that, juct plugged em in and off I went..

if you have a multi meter you can simply check voltage... I jumped fuse number 6 with an alligator clip and it supplied power to the fuel pump....(had my 11 year old help me so I could be on the bottom and checking while he engaged and disengaged the alligator clip)

as for running backwards... I dont think that would work - even poorly

so if I read this right you have a new pump and your old one, if the old one is dead... try and "jump it" on the bench and flip the wires and see how it sounds....maybe even try and run some non-flamable fluid thru it in a bucket, see if it works....as for the dead pump, my "dead" pump worked fine out of the car.... I suspect a couple raps with a soft mallet will get you thru the testing to satisfy your curiosity...

but I really dont think its required