Infamous pink wire

ALF750 · July 24, 2015, 10:46:21 PM

Job done, lets hope it lasts. Used the original wiring/fuse 13/H6 to activate a relay behind the fuse panel. Power via an in line fuse from the L connector on the back of the fuse panel, to the relay, then under the carpet and along the sill to the pump wire under the rear seat, all hidden and tidy (used heavier gauge wire also). Now to relay the headlights.

Colin Edwards · March 02, 2017, 08:38:16 AM

Just purchased a 1988 75 3.0. One of the minor electrical gremlins infecting it is a 13% drop in voltage from the battery to the fuel pump. I'm assuming this car only has the one pump given the fuel tank is behind the rear seat. On two occasion's now it has developed a lean surge - only during 30C+ weather. The most recent last Sundays AROCA drive - after almost 300k of trouble free running!
I understand one of the fixes for the voltage drop caused by the low cross section wiring is to run a significantly heavier +12V cable between the starter motor stud and a terminal block on the RHS of the engine bay adjacent the "Bosch Combination Relay". This is a logical fix given the apparent loading of the existing conductor, however I have concerns as this heavier cable does not seem to be protected. Does the 75 3.0 or any 75 for that matter feature a Fusible Link between the battery +ve and the rest of the car electrical??
The previous owner installed a high power sound system - now removed. There are two glass 10 x 38 fuses on the LHS of the engine bay adjacent to the battery. Could these be the fusible link/s? They look to have been added post manufacture. Maybe they are the feed for the now removed sound system. I'd rather feed the Combination Relay from a protected source especially if the new cable will have four times the current rating! Thoughts?

GTVeloce · March 02, 2017, 01:24:18 PM

Can't say WRT a 3L, but in the TS power for the fuel pumps comes from a relay in the engine bay, through fuse 13 in the main fuse box (under dash) and on to the fuel pumps. I would imagine the 3L should be fairly similar in nature.

Do you have the original manual? It should tell you what the fuses are for as a starting point.

Colin Edwards · March 02, 2017, 11:09:01 PM

The electrical schematic for the respective cars is similar but not identical. F13 feeds the fuel pump. F13 is fed by via SB1.5 so the majority of the fuel pump wiring is 1.5mm section - pretty thin given the current draw of the fuel pump. I'll check the SB1.5 and F13 connections. Probably end up replacing SB1.5 with a 2.5mm or 4.0mm cable and be done with it.

I installed a new fuel pressure regulator last night and drove the car tonight - all good! Maybe the regulator was suspect, however I'll still attack the wiring nevertheless.

GTVeloce · March 04, 2017, 01:43:13 PM

I ran a better (and newer) wire from the relay to F13 and then on to the pumps to replace that 1.5mm SB. From memory I just used 2.5mm. Seems to be holding up fine so far (after about 18 months).

Colin Edwards · March 05, 2017, 05:54:00 PM

Maybe Mr Bosch had it right but the bean counters at Alfa had it wrong. The new electric fuel pump I installed came supplied with blue (2.5mm) crimp lugs!!!

ALF750 · July 12, 2017, 04:43:49 PM

hope you have solved the problem, I haven't been on here recently! The 75TS has TWO fuel pumps, one in the tank and one out. The same power supply goes to both. I found on mine that the in-tank pump was NOT connected to the power, so only the external pump was working, and then was intermittent! A bigger wire direct activated by S13 (as per original message) to the pumps, bypassing any factory connectors, seems to have cured my ills. good luck. currently chasing stray electrons in a '95 Maserati - more fun:(

Colin Edwards · July 13, 2017, 11:46:02 AM

Hi ALF750,

My 75 is a November 1987 build 3.0 with the tank above the boot floor / behind the rear seats. Appears to have only the external fuel pump under the floor. Only wiring to tank seems to be for the fuel level sender.
I replaced the infamous pink wire with 4mm OFC cable when I installed the new pump and filter. The significantly shorter earth / return wire I changed to 2.5mm. Only seeing a 5% voltage drop now.

A future project will be to increase the conductor section of the cable between the starter motor and the fuse box via that connector / terminal block on the r.h.s of the engine bay. Under high electrical load the existing cable causes excessive voltage drop to the fuses and effectively the majority of the car electricals.

Methinks the lean stutter issue when taking off in high ambient temperatures was(?) / is a sticking Air Flow Meter flap. Engine idles fine, however when you open the throttle to drive off under load the airflow increases however the flap sticks or is slow to move causing insufficient fuel flow via the injectors / very lean mixture. The ECU still thinks the car is idling! Have to wait for the hot weather to return. Bloody cold in Melbourne at the minute!

Colin