Thanks for the inputs. I do think I've covered these steps. The
Gray wire on the schematic is "Gray or Tan/Wht" (mine is Tan/Wht).
I did unplug the fuse - and had 0V on both pins.
If the ORG wire were shorting to ground I would expect the ECMB fuse
to be blown... no it's not that - but upstream of the fuse. Probably
the ignition switch or wiring to the ignition switch. Seems more likely
the switch because other functions do turn on from the switch (so there
is power to it).
Applying power to the orange wire???... Well, via a 2A/6A battery
onto a 10A circuit it should be ok - even if there is a short somewhere.
I concur that via jumper cables would be a bad idea - but it won't
John Alt wrote:
Oh you mean for LI Motorcycling (not hotting the wire) - yea
I know NY has it's issues. I really liked NH, and Florida - where
I didn't have to wear one, there was no income tax, car ins was
optional. The Live Free or Die attitude beets everyone's heads up
each other's business.
Are you getting this information from an actual schematic? The reason
I ask, is that many people are under the illusion that the oil switch
is in series with the relay and can shut off the fuel pump if it fails, or
if the engine doesn't develop oil pressure. In fact, as far as I can see
by looking at an older schematic (and I know for certain on newer
vehicles), the oil switch is nothing more then a parallel circuit that
provides an alternative power source to the fuel pump in the event
that the fuel pump relay goes belly up while the engine is running.
No, if you lose oil pressure, you lose the pump. Pulling the oil
pressure switch connector will prove that. AFAIK, all TBI units were
like that. I have no idea about the newer units, but I have no doubt you
are right about them. I haven't had the good fortune to have to do any
real serious troubleshooting of the wiring on anything newer than 94.
I'd bet people getting left on the side of the road for a stupid oil
pressure switch or a corroded connector woke up someone at GM.
Computer terminal b2 is fuel pump input. It does not drive the fuel
pump, nor are there any other circuits to the pump except off the relay.
They grey wire powers the pump in prime mode, while the orange goes to
the oil switch, then connects to the grey wire to provide power during
normal operation. The grey wire is in parallel, but it is hot only when
the pump is priming. I had to look all this up when I converted a couple
trucks to TBI. The factory manual I have has the diagram I am referring
to on page 1a-57. This one is for the 89 Astro, which is the closest I
have to his truck with the same 1227747 computer. I know for sure there
are many, many errors in the Haynes diagrams. I can't find the post
where I talked about it, but I'd given some specifics about an S-10
blazer I was working on a few months ago.
That's interesting... I know there is paint on the blades of the oil
pressure switch - so the connection isn't reliable. Still that
matter until after it's started. Will probably try hotting the ORG
wire tomorrow if it's not raining (w/ a charger, not a jumper cable).
John Alt wrote:
Pay attention, young grasshopper. The orange wire is the battery input
for the computer. You don't have the battery regulating that line, since
there is no voltage on it. Now you are going to put a poorly regulated,
roughly 16V source with horrible ripple voltage onto your computer's
power supply. These computers are tough, but there is no good in doing
If you must supply power to this wire, do so with a wire slightly
smaller than the factory wire. Hopefully, if the smoke comes out, it
will be through your smaller wire and not the factory harness.
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