are the four relays on the relay board fully interchangeable??

jim

Yes. I just picked up some new aftermarket relays on Ebay for a decent price, if you need some.

thanks and i appreciate the offer - i have some spares - after removing me injectors and spark plugs - i realized i was definitely not getting fule - i pulled the fule pump and it was getting power but not coming on - i will replace it and see what happens.

thanks

jim

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My understanding was that the red relays were different from the black relays. Do a search on "+red +relay" and you should get additional information.

Eric Read

EDIT: Upon searching, I couldn't find my previous post... Anyway, the red relay is specifically for the engine. The black relays are totally interchangeable. I cannot remember specifically the difference between the red and the black relays... I think it had something to do with a delay circuit???? But I could be wrong.

Eric

Red relays have diodes internally connected in parallel with the relay coil. This is usually done to prevent reverse voltage spikes that occur when the voltage to the relay coil is suddenly interrupted. When the interruption occurs, the reverse current all flows through the diode instead of wreaking havoc somewhere else in the electrical system. Red relays are used for the fuel pump on many 911 models, but I think none were used on any year of the 914. Not at all sure why Porsche did this, and didn't use them for any other relays on the 911. I used to think it was because an electronic circuit, the speed sensor rev limiter, drives the fuel pump relay on the 78 and later 911s, and that circuit might be vulnerable to reverse voltage spikes. I notice, however, that the 76 & 77 911s, which just drive the fuel pump relay straight from the ignition switch, also use a red relay for the fuel pump, so that can't be the reason.

Anyway, the biggest consequence of swapping a red and black relay is that the polarity of the voltage that drives the coil is important for a red relay. If the polarity is backwards with a red relay, the diode will cause a short, whereas it won't matter with a black relay.