Wiring question, White yellow trace?

[Broadstone]

I have a autosparks harness on 1973 series III and would like to know what the white with yellow trace wire branching off the engine harness just before the alternator is for? Did I miss something as I cannot find it in the diagrams.

[TeriAnn]

I have a autosparks harness on 1973 series III and would like to know what the white with yellow trace wire branching off the engine harness just before the alternator is for? Did I miss something as I cannot find it in the diagrams.

That colour combination isn't listed in the '60s colour code I have but it is listed in a 1983 colour code as Ballast resistor to coil or starter solenoid to coil.

Unlike the Americans the British had (have?) a national standard for colour code insulation for different uses. I suspect the autosparks SIII harness is a universal replacement harness that includes wires used for very late SIII trucks. Late SIII coils may be a ballast type coil and the white yellow wire was a way to bypass the ballast while the starter motor was turning as a way to provide extra power to the spark plugs (easier starting).

Just a guess.

[siiirhd88]

On a late SIIA the white with yellow trace wire is for the oil pressure warning light switch.

Bob

[Broadstone]

It is located about equal distance from the oil pres wire and the ends for the alternator. It just seems an odd location. I guess I will trace it back and see what I come up with or just blank it off. I did refer to your site TerriAnn just before posting this question in hopes of figuring it out.

[jac04]

Could it be for the fuel cut-off solenoid on the carburetor?

[scatterling]

it could be for the cold start control switch

[Broadstone]

It will not reach the carb. or the cold start which is already wired up properly. Here is a picture if that helps.

[jac04]

^^Wait a second. In that picture the cold start warning light temperature switch isn't even installed in the head. You just have a blanking plate with 3 screws holding it in place. It looks like the wire would plug right into it if it was there.

[TeriAnn]

^^Wait a second. In that picture the cold start warning light temperature switch isn't even installed in the head. You just have a blanking plate with 3 screws holding it in place. It looks like the wire would plug right into it if it was there.

Except if the truck were fitted with a fuel mixture warning light the wire going to the fuel mixture thermostat switch should be light green/red.

Silly question, where does the other end of the wire go?

Also, why not ask the harness manufacturer where that wire goes?

The problem with a national standard for wire use colour codes is that it gets amended over time and we do not know which version of the code the harness maker is using.

[Broadstone]

Now we are getting somewhere. The choke switch is also white yellow as stated by Scatterling and has continuity between choke switch and the wire in question. Jac, this is my first NADA series truck and my previous home market vehicles did not even have this space to blank off, it was closed as factory I am pretty sure. So what temp. switch do I need? same as the other temp sender? and was it factory only on NADA spec. trucks. Really appreciate the help everyone!!