Fuel pump relay mod

[mas]

After 4 crank/no start situations (last 15 months) I am proceeding with the relay bypass mod.  Unfortunately, I only found the headlight mod under this category.  Well if someone says it is the same, that is like saying apples and oranges are the same since they both come from a tree.  If someone has a step by step on how to do the fuel pump mod please directed it my way.  I tried following the headlight mod directions but TLDR and found parts missing that led me down the road of confusion.

Aside from the clearer directions, I can not get my head around the issue in the first place, if the existing fuel relay is sometimes defective, and if we are tapping into the same wires of the circuit, what keeps the new mod from going u/s?  Maybe what I need is a circuit diagram showing the location of the existing fuel pump relay in respect to the mod fuel pump relay.

 

PS after the crank/no starts, I discoed the n111 bus and inspected both it and fuse 16 (all good), reinstalled them, turned the key and the fuel pump hummed!!

[MikeT]

The problem is not a relay in the SAM, but the tiny pins that take 55W+ of power to the low beams and fuel lift pump. The relay in the SAM is fine, but the pins are too small to move that much amperage and so the plug overheats, the plastic melts a bit and the contacts become intermittent. Mounting an external relay so only a signal voltage passes through the SAM is the solution.

 

A short term solution to an endless crank is to give a swift boot to the SAM then try again (worked for me a few times), but the proper solution is the relay mod.

 

I am not a fan of using an alternative unused power source from the SAM to run the relay high amperage circuits so I always advise running a new wire inside electrical conduit - with an inline fuse in this line - to the driver's footwell, and using that to power the low beam relays and the fuel pump relay.

 

Putting the relays in is quite simple other than the tight quarters - the correct output wires from N-111 are cut for the three units in question, and one end goes to the trigger circuit of the (4 pin) relay, and the other end is connected to the output from the new relay. I did not save the photos that showed all of this in the How To part of the former website, which is unfortunate, because I did this modification years ago and it's hard to describe it precisely without them, especially which pins are for which function. I just went into the garage and found my old SAM from Snowball, which indicates the pin that provides power to the fuel lift pump (because it's a bit melted at the base, sort of a blob around the base), the tenth pin to the bottom of the photo:

 

The direction of current flow is such that it goes out of the SAM on connector N-111 and to the headlight(s) and fuel lift pump. The purpose of the relay is to greatly reduce the amperage going through the SAM, thereby keeping the pins cool and stopping the melting issue.

 

Photo of the original N-111 pigtail that I replaced on the new SAM when the low beam headlight pins melted. They're the two in the centre:

 

Gratuitous shot of the SAM in situ:

 

Relay mounting strap in the car for the two headlights:

 

Edited November 16 by MikeT

[stickman007]

Too bad we lost the wiki section, I had a page with diagrams and explanation on how to do this mod….and alternatives to the headlights as well.