930 fuel pump relays, red or black

[ChrisBennet]

Hi guys,
All the 911SC I've worked on had red colored fuel pump relays.
I'm working on a 1980 Turbo now that has 2 black colored fuel pump relays. Is this normal for a 1980 Turbo?
thanks!
-Chris

[David]

My 79 has black relays. I've heard the only difference is the red relays have a diode to prevent reverse current.

[9dreizig]

Both of mine have black relays ( uhm oh yeah you know that!!)

[sand_man]

My '87 has red.

[Early_S_Man]

Undoubtedly, any cars with black relays for fuel pumps have had the red ones replaced with black ...

Obviously the black relays work fine for that application. I never quite understood exactly what was being protected from EMI in a CIS car, anyway!

[ChrisBennet]

Thanks guys!
-Chris

[Jim Sims]

"I never quite understood exactly what was being protected"

It was my understanding that the point of the diode in the red diode was to make a "free wheeling" disipative loop to deal with the inductive load of the fuel pump when the circuit was opened. This was to help protect the contacts within the relay.

[2.7RACER]

Jim Sims is one of the most knowlegeable members of this board, However, I've been studying the schematic. The diode is across the relay coil, not in the current path to the fuel pump.
This is to protect the contacts in the ignition switch.
Running the black relays will work, but the ignition switch gets more electrical arc when going from start to run with the black relay.
The diode minimizes the arc at the ignition switch, thus protecting the ignition switch.
May also ground some of the back emf from the starter solenoid since they are in the same circuit.
I would say with a black relay in the fuel pump relay socket the ignition switch will fail much sooner due to excessive arcing.

[Jim Sims]

I stand corrected. 2.7RACER correctly observes that the free wheeling diode circuit will not protect the internal contacts of the red relay. Upon further study, the diode circuit appears to be in place to protect the air flow switch. It is also interesting that the red relays appear in the CIS cars at the same time the air flow switch is first utilized. Not knowing if the air flow switch is sealed, I also conjecture that suppression of arcing in its contacts (by the diode) may have also been an attempt to eliminate a possible cause of the exploding air boxes. I don't believe the diode helps the ignition switch starter circuit contacts (at least not significantly) as they are not opening while the diode circuit is free wheeling - as the starter begins to turn the engine over and opens the air flow switch.

[2.7RACER]

I think Jim has nailed it. Thanks, it makes more sense that the small micro switch in the air sensor would need protection.
I further agree with Jim that my previous assertion that the diode was used to protect the ignition switch contact was incorrect.
Thanks Jim,