The previous owner installed a toggle switch under the dash that puts 12v directly to the lift pump with or with out the key. He just spliced into the wire before the pump harness. Is this ok, or is it a bad idea to bypass the relays and others (OPS).

ps. It runs fine without using the switch, he said he put it in so filling the filter bowl was easier.

I've heard of guys doing the same thing.I've got mine wired to the ignition switch so it runs whenever in RUN or CRANK mode.Have'nt had a problem in 9 years.

i got one,in case the OPS gives the ghost.

If I understand then it runs automatically when you turn the key on AND you have a switch to turn it on manually.

It needs to be running while the truck is running.

If I understand then it runs automatically when you turn the key on AND you have a switch to turn it on manually.


Yes, it runs as per normal via the key, As well as a manual switch. I figured it was fine but thought i'd ask

my 98 gmc pickup drove me nuts for 4 months
new tank , new lines , new lift pump , new injector pump , new electronics ,
still,,,every once and a while , it wouldn't start,,filter empty , fill filter with diesel , starts , runs mint !!!
came off battery terminal fuse box with wire to dash toggle switch,,to lift pump on frame rail

it works perfect

under normal conditions,lift pump runs when engine is cranking,,,then the circuit is disconnected ,,,it is then powered by 12 vdc through an oil pressure switch under fuel filter,,,gmc's bright idea , if truck hits tree and engine stops running , no oil pressure will shut off pump,,
so,,,always hit the tree hard enough to stop the engine from turning!!!!
so the only difference between wiring it through a dash switch or using the original oil pressure switch wiring ,, is that you have to remember to turn it off and on

i have forgotten to turn it off many times,,, no big deal
i am going to connect a dashboard mounted license plate light to the original wiring on the fuel rail and watch it as i drive to see if it goes out or flickers,,,indicating malfunctioning oil press switch.
then i'm going to take it out and beat the crap out of it before i throw it through the diesel shop's front window!!!
good luck
kevin