need4speed Posted March 5, 2013 Share Posted March 5, 2013 My little brain is having some trouble figuring out a few things regarding MS wiring. Please bare with me here, as when it comes to wiring im a wee bit fick....yes really!!Im using fuel pump STC4344 (shortened to fit in plastic TD5 fuel tank)Wiring diagram for megasquirt shows that there are WP wires going to quite a few different components.Brain fart 1. Rave shows that my chassis harness (2002 TD5) has 2 wires going to fuel pump. WP (pump to pump relay) and GB (pump to fuel gauge). So do i ignore the WP wire shown in the MS wiring diagram and assume i already have a WP wire going from pump to relay?Brain fart 2. Looking at the pic i took of my pump before modding/fitting in tank. it doesnt look like it has a WP wire at all...Brain fart 3. Looking at MS diagram there appear to be several different WP wires required for different components. In reality are these all separately run wires, or are they spliced into 1? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted March 5, 2013 Share Posted March 5, 2013 Brain fart 1: As long as your fuel pump relay is wired the correct way round (MS GROUNDS the wire to activate the coil, so it must have +12v on the other end of the coil) you're good. Brain fart 2: Wire colours matter rather less than what they're connected to - your fuel pump could have green polka-dot wires, as long as they're wired to the right things it doesn't matter. Likewise, just because the wire colour is correct don't assume that's all wired as you need it to be. Brain fart 3: It just denotes all run from the same relay (coils, fuel pump, lambda sensor heater). In reality, you could power the lambda and probably even the coils from ignition live if you wanted. Quote Link to comment Share on other sites More sharing options...
need4speed Posted March 5, 2013 Author Share Posted March 5, 2013 Ok thanks fridge. I understand. Next question is, im using one of nige's pre-built relay boards which have the fuel pump, and main relays incorporated into it. So what do i do with the relays that are already part of the main harness? Can i use both or should i ditch some? Does it matter? Quote Link to comment Share on other sites More sharing options...
Cynic-al Posted March 6, 2013 Share Posted March 6, 2013 None of my wire colours matched, some were part of the old loom some the new wires I put in. Some matched that diagram some didn't to suit how I fitted things. I would recommend keeping a log or diagram as you go along of your specific car as it makes fault finding at a later stage much easier. I would avoid 2 relays if you can, it will work but its unnecessary complication and increases the chance of a fault and makes later faults harder to find. If your planning on using the lr wiring for the fuel pump then I would keep that one, if your wiring fresh I would use the ms one. But that's just me ... Quote Link to comment Share on other sites More sharing options...
need4speed Posted March 6, 2013 Author Share Posted March 6, 2013 Thanks for the reply al. PaulMc has been helping via email. We have decided it would be better to ditch the LR relay (along with some of its wires i dont need) and use the relay on the MS board. Cheers Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted March 7, 2013 Share Posted March 7, 2013 Using no fuel pump relay means the pump will be running the whole time the ignition is on, meaning greater drain on batteries if you need to sit without the engine running but ignition on. More importantly, the MS ECU turns off the FPR when the engine isn't running, so in case of an accident and engine stall, it doesn't squirt fuel all over the place from a ruptured fuel line -basic EFI safety, I wouldn't do without it. Quote Link to comment Share on other sites More sharing options...
need4speed Posted March 7, 2013 Author Share Posted March 7, 2013 No im not doing without it. Im just using the FP relay on the MS relay board rather than the one in the main harness Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted March 7, 2013 Share Posted March 7, 2013 That was a reply to Cynic-al actually Quote Link to comment Share on other sites More sharing options...
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