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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: 3dachshunds on December 29, 2025, 11:02:19 AM

Title: No power to fuel tank 4 pin connector
Post by: 3dachshunds on December 29, 2025, 11:02:19 AM

Good morning everyone, I am trying to start new to me 1992 k100rs that has been sitting with half tank of gas for two decades! Well, after cleaning the inside of the tank as much as I could and replacing fuel pump, filter and lines, installed new battery, it does crank strong but the fuel pump is not running. So this is what I found so far: There is no load on 4 pin connector when cranking (measuring voltage across brown and green/white leads). All fuses are intact. Fuel pump relay appears working (solenoid clicks when applied load on terminals 85 and 86). The pump works when powered directly from the battery. So I am not sure how to proceed further. Any help appreciated!

Title: Re: No power to fuel tank 4 pin connector
Post by: Laitch on December 29, 2025, 01:52:20 PM

When the key is turned to On, can the fuel pump be heard powering up for a second or two?

Title: Re: No power to fuel tank 4 pin connector
Post by: 3dachshunds on December 29, 2025, 02:04:48 PM

No, definitely not doing anything.

Title: Re: No power to fuel tank 4 pin connector
Post by: Laitch on December 29, 2025, 03:03:27 PM

Is the Brick on its center stand or is it on its side stand?

Title: Re: No power to fuel tank 4 pin connector
Post by: 3dachshunds on December 29, 2025, 03:11:10 PM

On the center stand

Title: Re: No power to fuel tank 4 pin connector
Post by: Edward on December 29, 2025, 06:48:43 PM

For good measure, clean all your grounds before advancing. Also, it's worth sending out your injectors for cleaning. New iridium plugs would be a smart choice at this point. Clean your pump connector; it's often a problem area simply due to removing the tank for general maintenance over the years. Age brings on corrosion, which is the foundational mindset.