Guide for Replacing Alternator Output Cable
Based on 1989/1990 750iL:: photos below text
Symptom:
No obvious problem, discovered by visual inspection.
System voltage check showed only 11.5 volts, so battery condition was always poor.
Insulation on the cable badly cracked and failing at both ends of cable tube.
http://www.realoem.com/bmw/showparts.do?model=GC81&mospid=47354&btnr=11_0949&hg=11&fg=40&hl=20
Description:
After nearly 20 years of continuous service the insulation has failed.
While there is some argument that engine fires have been caused by
shorts through the cable tube to ground, one problem that cannot be
ignored is that the fine cable strands become badly corroded. Corrosion
→ higher resistance → higher current drop across the cable → higher
temperatures → cable fuses. The battery also does not get the full voltage.
Shogun's car recorded a charge voltage of 11+??? volts before
replacement of the cable and 13.2 – 13.4 after replacement.
BMW wants $830 for a replacement but you can do it for about 15$.
Time required:
About 4 hours: the nuts holding the cable tube to the engine head may drive you
crazy due to lack of space – drove me to drink fortunately.
Parts
· 80 cm length of high
amperage, high temperature welding cable (exact length depends on the
cable tube type – BMW kept changing the design so be careful about
retaining and duplicating the original cable) *** Key dimension is the
external diameter, must not exceed 12 mm to permit reinstallation in
the cable tube together with the Oil Level Sensor Wires
· Shogun's final cable: 140 A. Fujidensen WTC 22 sq mm,
12 mm OD,
high temperature and flame/chemical resistant. For good measure he
wrapped it with Nitoms Proself, a thin heat resistant tape – looks
silver in the photos.
· 2 eyelets
· Shrink tube to suit eyelets/cable
· Bosch 1928402452: 3 pin plug to replace Oil Level
Sensor plug at Battery Post. If it has failed.
· Male flat pins for this plug: Hella B 187, 050-1.00
mm2, 2.8 x 0.8 mm
The Dirty Work Begins
· Disconnect
the battery.
· Release the 3 electrical plugs starting with X-11 and
move them away from the Battery Post
· Remove the cover from the Battery Post by lifting the
inside vertical side and then moving the cover outwards.
· Remove the 13 mm nut holding the cable to the Battery
Post - then the cable.
· Unplug the 3-pin connector for the Oil Level Sensor
and release the
3 pins from the holder (if still good condition) Note the location of
the 3 colored wires and release the pins if possible. Our plug just
fell to pieces so the pins were undamaged.
· Remove the LHS MAS and intake boots, and the air
filter.
· Remove the LHS distributor cap, plugs, and the 2 10mm
acorn nuts
holding the plug wire tray – remove the whole sheebang to get some
space. Good idea: check the condition of the distributor center pin
etc. Alternative is to remove only the plugs from the distributor cap –
make sure you know which plug goes where, aftermarket caps and plugs do
not have the BMW markings.
· Remove the 2 10mm bolts holding the cable tube to the
rubber mounts
on the head – one of ours failed through the rubber so it's a wise idea
to have some spares. NOTE: if you have to remove a broken rubber mount
put the spanner on just the nut attached to the rubber, there are 2
nuts next to each other. Point: on this model the
rear bolt requires a very short 10mm spanner – say only 5 cm long – for
good clearance.
· Unscrew the oil filter mounting bolts and tie the oil
filter as far back as it will go.
· You need 13 mm and 10 mm wrenches with fine ratchet
and swivel neck for clearance. We created one as shown.
· Remove the cable and sensor wire from the alternator.
· Note the distances of the eyelets and plugs from the
ends of the cable tube.
· Cut and remove the cable, measure length and
replicate with new
cable. NOTE: the 3 Oil Level Sensor wires are still attached so do not
put any pressure on them.
· Check the 3 Oil Level Sensor wires for damage – ours
looked to be ok.
· Reinstall the 3 Oil Level Sensor wires and then the
new cable. You might need dry lube to work the cable up the tube.
· Add the eyelets – we crimped them using 2 axes but if
your teeth are strong go for it.
· Adjust the the distances of the eyelets and plugs
from the ends of the cable tube.
· Installation is reverse of above.
NOTE: please take all care and remember that all repairs are at your own
risk.
Insulation failure due to heat - this cable lies just above the exhaust header !
Corroded wires - less copper = higher current loss
Parts
Plug-wires labeled
Ad-hoc
wrench for alternator nuts -- the handle must lean towards
the front of the car for clearance -- fine step rachet is essential !
Old & New eyelets
Crimping axes
Cable lubrication - silicon spray used
Reinstallation
