Supplemental fuel pump relays

Search threads for ones that I started; I did both fuel pumps and radiator fans.
Ken <Southjersey400i>

 

Fresh pumps draw a lot less current, and compared to other ancillaries in this car the wiring of the pumps is quite clean (short ground, no intermediate connectors), so no huge power loss across the line.

Instead of butchering the wiring, I'd try first new pumps and conductive grease on the relay pins, connectors and fuses (one of the member here had great success with MG Chemicals silver conductive grease), if this is not enough, the traces on the relay box can be beefed up. This is what I am currently doing on mine, no guarantee it will be perfect as I've not tested it yet... If you really want additional relays, then you can attach the relays to the pump, use the existing cables (clear brown?) as the signal for the relay, re-use the existing ground, and feed the positive through a cable that is connected to the battery. This cable can be routed along the frame ladder, up to the battery, and as suggested earlier this week you should add a fuse box next to the wiper pump. Once this is all working I would add a few layers of conformal coating to the relay, as it will be exposed to dirt debris and water.

I do not like the idea to tap directly high current accessories to the battery, as it does not pass through the ammeter, so you loose the capability to see that something is wrong with the accessory: when you turn the key but do not ignite the engine, all the current is provided by the battery, so passes through the shunt, if I see a huge amp-draw when I turn the key on, I know something is wrong with the pumps. Similarly, when I switch the engine off, I can see if the fans are drawing more than usual. Loosing this feature is a bit annoying.

 

My '84 400i has no ammeter only two lights, one for each alternator. I think earlier cars had ammeters. It is useful for all the reasons raemin stated.
Ken

 

Or a new fuseboard ! Looks like OEM but much more secure.
Here is an installation manual and more information :
https://redbaycars.com/onewebmedia/Manuals/Installation%20manual%20Fuse%20Box.pdf
If you have more questions, dont hesitate to ask me.
Guido