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fuel pump relay question

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jvandyke

jvandyke

Luke Skywalker
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See if this makes sense, since I'm rewiring everything, car has electric fuel pump, I want it switched since I have occasionally forgotten to turn it off, so.
toggle switch under dash, with feed from ignition, switched side, other side of toggle to relay, 86, 85 grounded, 30 hot off ammeter, 87 to in line fuse to fuel pump's hot. I'll mount the relay behind the dash.
I just don't want too much amperage through the ignition switch (or isn't a relay really necessary on a fuel pump).
 
If it were necessary they would have done it from the factory. It's really as simple as that. Why introduce complexity? The real limit of the switches as they exist from the factory is the number of uses, not the current carrying capacity. One more thing to go wrong.

My 2¢
 
With the low volume/pressure pumps required for these cars a relay is not necessary. However, an inertia shutoff might be advisable. You can get these from a junk yard for a couple of dollars.
 
Wasn't the MK1 a fully mechanical fuel pump? The factory didn't plan for it all, right? Now I'm adding an electric device (has been there for years) pulling current off the ignition switch (which I just rebuilt and would like to preserve). But if the current draw isn't a factor, maybe I won't bother.
My alternative reason was to have an idiot light telling me the pump is off. I could use 87a off the relay to a light, so if I turn off the pump, as soon as I turn on the key the light goes on telling me my pump is off, toggle the pump on, light goes out. Of course you could argue the pump makes enough noise you'd better know if it's off! Wait, I guess I'd have to use a switched power source for the relay then which would kinda defeat the purpose, okay, bad idea.
Overkill, probably. It's not like I don't have enough wires to deal with.

Inertia shut off, or oil pressure cut out is probably really wise. I did not have one on my Opel GT that I wrecked. I had the presence of mind to hit the switch after the head on, but it wasn't necessary, all electrics were dead on impact.....that time.
 
I don't think you want a separate switch for the fuel pump, if that's what you're contemplating. It should go on and off with the ignition. I have a single relay that controls all of the switched power, so the ign switch just switches the current to the relay coil. That's a simple solution if you are concerned about the switch current, which is not an unwarranted concern, in my opinion.

Yes, the inertia switch is also a good idea. I probably should get one...
 
PO had fuel pump separate, always hot. Had to remember to turn it on and off as part of the starting/stopping procedure. I don't like that so it will be switched source now to come on with the key but it will also have a separate toggle to disable it when needed. A relay for all switched devices is a good idea though. I could rig an idiot light if I used a SPDT toggle for the pump, but how often would I turn off the pump when the key was on? Depends on how I wire the radio I guess. Sometimes I like sit and listen to tunes waiting to pick up kids from soccer practice and such, so either I wire the radio hot or put an idiot light on the fuel pump. Ask my daughter how often I took off after picking her up only to stall a few seconds later (because I was listening to the radio and had turned off the fuel pump)......
 
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