cold start solenoid

[cmcfaul]

Is the cold start solenoid activated by one of the two yellow wires at the starter?

I replaced the starter wires with a single wire running into the ignition switch and the car has been difficult to start when cold. If not, what causes the cold start solenoid to work (squirt fuel into the stacks).

There were two yellow wires running to the starter. What does the second one do?

Thanks,

Chris

73 911 E

[Flieger]

Thermal-Time switch in the crankcase breather cover is the signal. Not sure where the power comes from.

[blucille]

on my '72, which has a CIS 3.0 from a '79 SC, yes. When I replaced the starter I connected both yellow wires together to the lug on the starter solenoid

[letsrollbabe]

I think one of the yellow wires comes from the ignition switch, and the other from the harness that goes over the top of the engine, so the starter connection is simply a terminal point. The yellow wire then runs through the engine harness, and one short length then connects (T's into) to the thermal-time switch. A single yellow wire goes through both 14 pin connectors to get the cold start signal (from ignition switch) to pick up the start relay, which then send 12 v to the cold start solenoid.

I recently had a problem with my cold start solenoid not working even though it had a voltage signal, but it was 9-10 volts for whatever reason and wouldn't pick up the solenoid. My solution after doing a lot of trouble shooting with various parts, relays, checking resistances, etc. was to use the rear defroster switch circuit to turn on the solenoid, since I no longer have a rear window with heating lines (912 glass). The defroster is turned on with a black wire under the relay console with a male/female connector so it is easy to access. When the defroster switch is pulled, the black wire gets 12 v (when ignition switch is on), so I made up a wire to plug into the black wire running to the solenoid. When I want to start a cold engine, I turn on the ignition for a few seconds and simultaneously pull the defroster switch for 4-5 seconds (then off) and then turn the key farther to kick in the starter...and it fires right up. You can do the same with a new switch mounted under the dash that gets 12 v when the ignition is turned on, and feed the wire back through the tunnel. Another option is to use a green/white wire that runs from the dash through the tunnel to the 14 pin connector that is used for the rear fog light option. I didn't use it as the black wire was so accessable. The green wire is usually tied off in the fender well near the driver tail light box. It could easily be brought up through the rubber engine gasket to the cold start solenoid.

Back to the orig. wiring scheme, the yellow wire provides 12v to pick up the coil on the start relay (either pin 85 or 86), which then allows the 30 pin to send 12 volts through pin 87a to the cold start solenoid. The thermo-time switch grounds the 12 v signal when it heats up so the start relay coil won't get 12 v when trying to start...until the bi-metal cools off. You can check for continuity from the 87a female connector on the relay console (round relay plugs into) to the wire going to the cold start solenoid. You can also put a voltmeter on the disconnected wire to the solenoid to see if it is getting 12 v when the starter switch is in the crank position (need 2 people or an extender wire to allow the voltmeter to be in your hand when you turn the switch to start). You can also check to see if the solenoid will operate with a 12v signal. Use a jumper wire from the #1 fuse (switched 12 v) for this and you can hear the solenoid click when the ignition switch is on.

These circuits over the years have been a source of problems for these cars, but things can be worked out to fix the problem....good luck.

[cmcfaul]

GREAT, so my theory is correct. I have to connect one of the yellow wires to the active (new) starter wire. Figuring out which one is the old starter wire, that used to run to the ignition switch, and the other, which is the one I want to give 12 volts to when the starter is engaged is going to be a 50 / 50 chance unless I get fancy with a volt meter.

Thanks a million

Chris

73 911 E

[blucille]

I believe it's easy to tell, one comes from the interior compartment harness, the other goes up and over the tranny towards the drivers side of the motor...yes, they are both wrapped in a larger harness, but there should be some good hints to make an educated guess.

[edmayo]

The wire sizes are different, larger is from the ignition switch.

[ThomasTe]

I recently had a problem with my cold start solenoid not working even though it had a voltage signal, but it was 9-10 volts for whatever reason and wouldn't pick up the solenoid.

I have the same issue, 9-10 Volts at the yellow wire to the thermo-time switch, (with the wire removed from the thermo-time switch).

With the ignition switch on, I got 12,3 Volts at the male connector for the same yellow wire at the 14-terminal multi-connector at the engine electrical panel, (with the plug for the engine wiring harness removed).

So the voltage drop occurs somewhere in the engine wiring harness, I guess? Or maybe because of some fault in the harness? Could the connection to the starter (yellow wire at starter terminal 50) be the cause of the voltage loss? And will it be safe to disconnect it to see if this makes a difference?

Any other ideas what is causing this voltage drop, and how to fix it? Or what to check next?

Seems like the solenoid on top of the fuel filter console does indeed need 12 V to work.