Wiring to Replace or Not, While the engine is out Options

[DennisV]

How problematic is the now 50 year old wiring? Some existing threads seem to suggest they're pretty vulnerable, yet I don't see wiring harness included on most "while the engine is out" todo lists.

Are there any that are consistently so troublesome that they should get proactively replaced even if they appear good? On the 914-6 it appears there are two for the engine bay (complete engine and alternator). That's $500 USD right there.

For reference, I'm not attempting a complete restoration. Just trying to get our car safely and reliably back on the road. The engine, transmission, and suspension components are out of the car. I've found a couple previous owner wiring additions, but they have been easy to remove.

My impression has been that if the wiring, insulation and connectors look good they probably are good. It's not like the copper wears out. Perhaps this is naive.

P.S. New plug wires are already obtained. I have no intention of removing the main harness.

[TheRuttmeister]

I'll add that a normal multi-meter can't provide accurate readings at really low resistance, so don't go getting worried if your cable should be 0.5ohm but reads as 1.5ohm.
Corroded cables or connectors will bump that number by a lot more than a couple of ohms.

[Superhawk996]

I'll add that a normal multi-meter can't provide accurate readings at really low resistance, so don't go getting worried if your cable should be 0.5ohm but reads as 1.5ohm.
Corroded cables or connectors will bump that number by a lot more than a couple of ohms.

While this is true with a cheap $10 digital multimeter any decent meter can read fractions of an ohm.

My cheap Ames Digital Multi-Meter (DMM) from Harbor Freight reads a 0.6 ohm resistor accurately. Likewise putting two of them in parallel reads 0.3 ohms. Sometimes jumps to 0.4 ohms which is due to the 0.1 ohms of resistance when the leads are shorted. EDIT: pulled out a 0.15 ohm 10% tolerance resistor, Ames meter measures it as 0.2 ohms.

With a DMM you just need to be aware of the offset of the meter leads themselves are. Good leads should be 0.1 ohms or zero when shorted. My Ames meter bounces between 0 and 0.1 (smallest resolution it will display) - leads are probably about 0.05 - 0.07 ohm and the meter rounds that up to 0.1 ohms.

Most analog multimeters have a zeroing potentiometer that allows the resistance of the meter leads to be zero’d out. I have an old school Radio Shack Analog meter with a 1 ohm scale that easily reads to fractions of an ohm.

A 1 ohm resistance gain in the yellow starter solenoid circuit will result in a no start condition.

In fact, even a 0.5 ohm gain in the starter solenoid circuit will cause serious problems because that solenoid pulls about 25 amps when operating normally. An incremental gain of just 0.1 ohms will create a 2.5v voltage drop if it’s in a circuit pulling 25 amps. The problem is, the solenoid circuit won’t even be able to pull proper amperage due to high wire resistance, and without enough current flow, the solenoid doesn’t work.

Bottom line: if you have a DMM that can’t measure fractions of an ohm, get a decent meter.