On Tue, 23 Mar 1999, Mike Lishego wrote:
> Hello all,
> Had a rather unfortunate adventure in the 'B today...Started up
> the car to go to school and got out of my parking place when the car
> quit DEAD. I sat there, thinking the alternator was shot and
> wondering how I could get to school. Suddenly, a big gust of smoke
> rose from my steering column! I jumped out of the car and quickly
> disconnected the battery to minimize damage.
> I wasn't far from my parking spot, so I pushed the car back into
> place and sat down to think...At this time, smoke started coming
> from my passenger's side seat! I ran to the battery and found that
> my 'constant ground' wire that I run to keep my radio settings was
> smoking! It was pulled from the battery, and all was well (at least
> as well as it could be.)
Constant ground?? Not unswitched power? this will become an important
distinction...
> The DPO used some silly thin-gauged wire to run the fuel pump.
> This wire ran right under the passenger's side seat. It cracked,
> and you guessed it, burned. I pulled the steering cowl off to find
> the white wire melted, along with my ignition switch. Any hopes of
> a cheap repair went down the tubes with that discovery...
> 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.
> So, what's next? All the carpet and interior pieces are OK,
> with no real burn marks. 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.
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.
> for a new ignition switch. My question is simple - why did the
> white wire melt? It wasn't even connected to the fuel pump, though
> the pump wire came from the fuse block at the same spot where the
> white wire went in. I checked the end of the white wire, and it was
> melted too. I cut it and re-shrink wrapped it to ensure that no
> accidental contact would be made.
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*.
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.
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>).
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).
eh. Fun.
--
John M. Trindle | johnt@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire H Stock | '88 RX-7 C Stock
|