>On Tue, 23 Mar 1999, Mike Lishego wrote:
>
>Constant ground?? Not unswitched power? this will become an
important
>distinction...
There's a reason for that. I have a battery cut-off switch that I
use on my ground terminal. I disconnect it every night because a) I
don't want my battery to drain for a silly reason, b) nobody can
steal my car if it won't start, and c) nobody can crawl in my car
and leave the lights on *been there, done that.* I ran a full-time
ground to the radio only because I wanted to keep my stereo settings
for more than a day.
>> Along with this, the remote ground wire that I had run for my
>> stereo melted too. I *ass*umed that a ground (especially to a
>> battery post) didn't need wire that was too thick. I guessed
wrong.
>
>No, you were right, if all that is being grounded is the radio.
Actually, it's the radio and the circuit it's on. That would
include the map light (Which only works through the switch, not with
the doors), the cig lighter which is disconnected, and the trunk
light. I don't think that's too much to ask from a circuit that
sees limited use?
The radio only takes it's power from the circuit when the car is on,
but the whole set-up is gounded and has power when I had my
permanent ground wire connected.
Obviously, I get to spend some time buying
>> thicker gauge wire for my stereo and fuel pump, along with some
$$$
>
>Fuel pump, maybe. Stereo, no.
Picked up some 10-ga wire from Autozone today. Gonna solder the
connections and heat shrink them tomorrow...
>By the way, on my stereo installations both the
constant(unswitched)
>power for memory backup and the switched power lead are fused.
That's how
>they come in the factory (stereo factory) harness.
Right, my stereo is like that. However, since the cig lighter
circuit sees power at all times, my radio won't switch off with the
ignition switch. I think I'm going to change this with the new
wiring. I've got a mind to run a hot wire to a fused circuit on the
fuse box that will shut off the radio with the key.
Would I have any problem running a ground to the battery from the
radio only in this situation? What about the trunk light (it is
nice to open the trunk to turn on the battery and have the light
come on for you...)
My question is simple - why did the
>> white wire melt?
>
>Well, it seems pretty clear you had a short-to-ground, which pulled
too
>many amps through the ignition switch. That's what melted *that*.
Yeah, that fuel pump wire actually burned through itself to the
ground...Bad news when that happens...
>If you had a "Constant ground" wire that melted, it means that too
much
>current was supplied to *it*. If it was really a ground wire that
means
>something high current was using it *instead* of its regular ground
path.
>This implies an open ground connection elsewhere (such as, oh, the
ground
>strap on the block) and/or a short between this wire and hot.
OK, the radio was a constant ground. I tried to not use the stereo
without the battery connected to the main harness (ie - all the
grounds), but I might not have a few times. That's where the
problem probably started...
>If it was a constant voltage, instead, it means that *it* was
shorting to
>ground, bypassing the stereo.
>
>I'm confused by the wire running directly from the ignition switch
to the
>fuel pump, instead of into the harness. This sounds like a DPO
>modification. If it *is*, it implies there is something wrong with
the
>normal route through the harness. Like, say, a previous fire has
melted
>the insulation inside the bundle, shorting wires together (go
ahead, ask
>me how I know <g>).
I'm not sure if this hack is due to the harness or the pump...I have
an aftermarket pump on the car, but the white wire is also hanging
down by the fuel pump. When I looked under there, it was freshly
melted, along with a black wire coming from the wiring loom. I cut
them both to where I could see separate wires again, then taped
their ends off. Dunno what the black went to though...
I'm looking at my hayne's wiring diagram right now...It *seems* that
the fuel pump's white wire gets juice from the ignition switch and
also from the fuse block. If I disconnected the white wire from the
fuse block that runs to the fuel pump, this would solve any
potential shorts, right? No, I take that back - it would still get
juice from the switch. Judging from the diagram, I'd have to find
the connection where the two wires meet on their way to the fuel
pump and disconnect both of them. Anyone know where that is?
The black wire intrigues me...I never knew MG fuel pumps weren't
grounded to the body! Hmmm...I see that this wire also supplies a
ground for the rear right-side lights. Could this disconnected
ground be the reason my right turn signals blink slower than the
others? I guess I'll see - once both white wires have been disabled
at the fuse block, I should be able to connect the nblack to ground.
>Summary:
>The stereo wires shouldn't have melted if all they were attached to
was
>the stereo. The fuel pump wire doesn't have to be *that* thick, if
all it
>was powering was the fuel pump. Bypass wires tend to indicate
harness
>problems. Ground wires melt due to suddenly becoming the best
>path-to-ground, hot wires melt due to the disappearance of proper
load
>(shorts to ground).
Thanks for the tips...This wil definetly help me in my search for
electrical salvation!!!
>eh. Fun.
>
>--
>John M. Trindle | johnt@tsquare.com | Tidewater Sports Car Club
>'73 MGB DSP | '69 Spitfire H Stock | '88 RX-7 C Stock
>
"You have children - how would you feel if your kid caught on fire?"
-My quote of the day, 3/23/99
Michael S. Lishego
http://www.mgb.bc.ca/virtualgarage/
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