A warning related to battery cables - don't let your car catch fire!
 

So yesterday Iridium and I pulled his glow plugs, reamed the openings, installed new Bosch plugs, etc. It was a mix of preventative maintenance as well as an effort to correct a bit of a slow, stumbling start on his '84 300D.

In the process we pulled the injector hard lines. Turns out he also needs a new primer pump (he has the old style and while it's not leaking, it is also not pumping worth anything!). That all meant that he was going to have to do a bit of cranking to get his lines purged of air and the engine running.

Well about 5 seconds in to his first cranking attempt I yelled - STOP!

His positive battery cable had begun smoking :eek:

I'll save you the story of some of the investigation we did but we found that the clamp on the end of the battery cable at the battery was getting so hot it was melting the metal of the clamp. After letting the car sit a bit he tried to do one more short crank and --- nothing. Dead. No power. The battery cable had just bitten the dust.

It was easily fixed with a new positive cable. The auto parts store doesn't carry positive cables of any reasonable length in anything large than 4ga so he'll watch it and likely plan to make up some 2ga cables in the near future. We also replaced the ground with a 2ga cable while we were at it. Bottom line - problem solved, car started.

The investigation in to the cable itself showed bad internal corrosion, which lead to increased resistance and therefore heat! The picture doesn't quite do it justice - the inside of the cable was very discolored and overall nasty looking.

http://i.imgur.com/aykbAwY.jpg

So the lesson here is that after 30+ years in operation even a simple cable can be considered a wear part. Inspect those cables as best you can, and replace them if necessary. Thankfully replacing the starter cable is fairly straightforward.

1) disconnect positive cable at the battery
2) under car, at upper front of the starter, un-do the 17mm bolt holding the positive cable in place
3) remove the phillips screw holding the smaller wire to the starter
4) Cut the wire tie holding the block heater wire to the stater wire harness (if applicable)
4) pull harness out through a grommet that holds it tight to the inner rear of the fender
5) cut end off of starter cable and pull it out of the harness wire sheath
6) put new cable in to sheath
7) reverse the process to reassemble

It would be interesting to know how much voltage drop would be measured between the battery & starter.

alteration to your list...

DISCONNECT NEGATIVE CABLE FIRST!!!

Indeed! Thank you.

Iridium cut the cable open today and found bad corrosion going about 6" down the length of the cable, and found that some of the wires inside the cable were starting to melt the insulation from the inside out.

He noted that the corrosion was primarily affecting the internal winding of wire down the middle of the cable.

He did test for voltage drop across the remaining cable, however his 12v power source only provides less than 1 amp and there was consequently no evidence of voltage drop. The voltage drop at the amperage pulled to start the car would probably lead to very different results.

We couldn't really even test the issue, either, as the cable deteriorated to the point of no longer working (as noted in the first post) after the smoke-generating cranking that started us down this road.

http://i.imgur.com/UXE4kcL.jpg

Would you source two gauge cable from an electrical supply place? Like same thing you would use in a commercial AC application? Ive been wondering about this.

People on the Cummins forum say there are some welding cables that work well.

Here's one guy that makes them for sale. I've heard good things about his builds.

Heavy Duty, Aftermarket, Custom Battery Cables for your Car, Truck or RV

I made some jumper cables out of welding lead, so I could make long ones that would jump a diesel. It's a little thick for battery cable, but maybe they make something smaller.

Problem is buying them. New are expensive. Buying by the foot from an electrical house, wouldn't be bad.

I have a buddy that's an electrician. I was gonna replace my ends but this is motivating to replace the whole cable.

My starter ground is a ground strap for a commercial application, works great.

This is done in case the wrench slips while working on the positive terminal then the wrench contacting metal ( ground ) causing a dead short.
Otherwise it doesn't matter. And, if an old British car, disconnect the earth ( ground ) and not the negative terminal as these cars are positive ground.

MBGs circa 1975 were 12V negative ground as I think were MGAs. Perhaps 60s era Sprites were + ground.