1987 Starter Solenoid Wiring

Boxer 6 · 06-19-2007, 06:10 PM

I've got a question to throw out to everyone. I have three wires to connect to the solenoid. A black wire, red wire and thin yellow wire. I know where the black and red wires go. Where does the yellow wire go? Is it at the six o'clock position? Pictures would be great. Thanks in advance.

Early_S_Man · 06-19-2007, 06:54 PM

The Yellow wire is terminal #50 from the ignition switch, and it goes, curiously enough, to terminal #50 on the solenoid. As the Yellow lead is terminated in a .25" Faston or small M5 ring terminal, there won't be any confusion with the M10 ring terminals on the Red and Black leads!

buttjoint · 06-19-2007, 06:57 PM

Which means, They will only fit one way.

peritus · peritus's Garage

I R/R'ed mine a few weeks ago and took this photo so I could get it back on properly. Hope this helps.

peritus · peritus's Garage

The yellow solenoid wire should connect to the top of the solenoid when installed. There is (on mine) an extra male connection on the bottom, but that's not the right one.

88911coupe · 12-27-2014, 12:29 PM

Have a question...if I wanted to test whether or not the yellow wire was getting sufficient power during starting I would remove the yellow wire and test it with the key in the "start" position with a meter hooked up with one end on the wire and one on the ground...correct? I should see close to 12 volts? I have confirmed I see the same power on the black wire connection on the starter as I see at the battery (about 12.55 volts) so that tells me the black battery cable is solid?

Tremelune · 12-27-2014, 09:03 PM

You are correct. With the ignition to "start", the small yellow wire should have 12v. Be careful when testing the starter. If connected, it will spin and could move the car if it's in gear.

What is the greater issue? Starter won't spin? Just clicks? Slow turning?

88911coupe · 02:30 PM

Thanks for the reply. Basically what has happened is about 3 months ago car began to have starting issues, sounded a little odd when starting and sounded like starter was struggling. 3 year old Die Hard was having trouble holding charge but new Bosch battery has not solved problem. Seem to have full power on black cable at starter so now seems like it might be either the yellow wire power to solenoid or maybe starter is starting to go. It was replaced (rebuilt unit) about December 2011. I get 13 V, maybe more when running. My intent it to see if I'm getting good power to the solenoid, then if that checks out I guess its probably the starter going bad. Does that make sense?
UPDATE...just "tested" it and with the yellow wire removed from the solenoid I'm getting 11.96 with ignition in "start" position so does that indicate an issue with the starter?

Tremelune · 12-28-2014, 12:48 PM

Note that voltage doesn't equal current. You can have 14.4 volts at the solenoid but cables that can't carry the load.

Random idea: I believe the starter is grounded via the transmission, which is grounded via a strap that is easily corroded...Might be worth eyeballing.

88911coupe · 12-28-2014, 01:32 PM

Thanks, the ground strap was replaced about 2 years ago and I did remove it and clean it up. I suppose it could be causing problems though...I really struggle with electrical issues!!

The cap'n · 12-28-2014, 01:50 PM

You want to test the voltage on the "50" wire with it connected. In fact, you want to check the battery voltage on the starter cable with it connected and while cranking. SCs (and possibly later cars) are known to have battery cable breakdowns just after the cable leaves the battery. The best tests for voltage at the consumer connection are done under load. Might want to do a voltage drop test, both under load and at rest. Furthermore, a 3 year old battery is NOT above suspicion. Sitting time, load, charging, and climatic conditions can all cause a battery to underperform or shorten its lifespan.

The Cap'n

88911coupe · 12-28-2014, 02:48 PM

Just put new battery in.

88911coupe · 12-28-2014, 04:43 PM

OK Cap'n thanks for that suggestion. So I need to hook up the meter to the end of the yellow wire connection after reconnecting to the solenoid. I'm concerned about being able to get the end of the lead up there to test it, it is really tight up there. Also, what am I looking for as far as readings...what will they tell me? Thanks for the help!

The cap'n · 12-28-2014, 07:10 PM

You're looking for the voltage delivered to that pin while in the crank mode. It should be pretty close to battery voltage, IMO. Maybe a volt or so lower.

The Cap'n

911pcars · 12-28-2014, 09:42 PM

Quote:

Originally Posted by The cap'n

You're looking for the voltage delivered to that pin while in the crank mode. It should be pretty close to battery voltage, IMO. Maybe a volt or so lower.

The Cap'n

System voltage at any point in the electrical system will drop since the starter motor needs electrical energy to crank the engine. If the battery is good, voltage should be 9.5 - 11 volts while cranking.

Thus while cranking, the voltage at the end of the yellow #50 wire should be the same as the cap'n stated.

To confirm this (or any) circuit isn't suffering from excessive voltage drop (corroded or loose connections), connect the + and – voltmeter test leads to the ends of the circuit segment you want to measure. During cranking or load activity, V drop should be >.1 volt. Excessive Vdrop for the tested circuit could prevent the solenoid from connecting battery to starter motor as designed.

Sherwood

sc_rufctr · 12-28-2014, 10:21 PM

Does this help?

Note: I've placed a relay in my starter circuit hence the extra wires.

Tremelune · 12-29-2014, 06:13 AM

A solenoid is basically a giant relay. The trigger wire doesn't need much juice at all. Everything flows through the big wire and the chassis/transmission/motor.

88911coupe · 12-29-2014, 06:13 AM

Thanks, I was a little confused last night when I tried to hook up the yellow wire back to its tab on the solenoid when it appeared I found an "extra" tab. Now I can tell that its actually just a "dual tab" connection, I guess to make it more flexible. However this now provides me a tab to hook an alligator clip onto the #50 solenoid connection to do a test. To do this I'll hook the VM's pos lead to the extra tab on the solenoid and the neg lead to the tranny ground strap, attempt a start and watch the meter...correct?

911pcars · 12-29-2014, 08:56 AM

Yes. While cranking, you'll be observing system voltage, maybe the same as if connecting the VM to the battery posts. If it's not, maybe that circuit is suspect.

Since the yellow wire is only active during cranking and you want to test and confirm the yellow wire circuit (#50) is receiving full circuit voltage, you must disconnect it from the solenoid. Thus, with the ignition switch in the crank position, the voltage at the end of the disconnected yellow wire should be pretty close to system voltage (~12 volts).

To test the yellow wire while the engine is cranking, connect the VM to the where it starts (ignition switch) and where it ends (at the solenoid). This tests for voltage drop (or loss of voltage due to excessive resistance) in that section between the test leads.

If the drop is >.1V or so, there's excessive resistance in that circuit. The starter solenoid requires close to 10-11 volts to successfully energize the starter motor. If you want to include the ignition switch in the Vdrop test, reconnect a VM lead to it's power source, typically the fuse box (it's no. 1 fuse on my early 911), and retest; that is, crank the engine and observe the voltage. Check connections for corrosion and tightness.

The above is a generic test for any electrical circuit. In summary:
- With load OFF (e.g. bulb), ground the neg. VM test lead. The pos. VM test lead can probe along any portion of circuit for available voltage (target is 12 volts).
- With load ON, (e.g. bulb switch ON)VM test lead at each end of suspected circuit component/path tests for voltage drop (<.1 volt for path and connections; about 12 volts for the load). Use internet search engine for a longer, more thorough discourse on the subject.

Hope that's not too confusing.
Sherwood

88911coupe · 12-29-2014, 07:04 PM

Ok now really confused...I hooked up the VM to the extra solenoid tab that is part of #50 then to the ground strap. Had wife turn ignition which sounded very weak and failed to start car, noted that I did not see anything on the meter! WTH? I obviously did something wrong. I will say that when I pulled the yellow wire off the solenoid and hooked it up to the VM and ground I got the same V as at the battery when the key in start position.
Then decided to check battery which was about 12.3 so hooked up a battery charger...started with a bit of effort. Measured just over 14 V on battery while running.
Next step is to follow this from Sherwood but need to get clear picture of exactly how this is done.

To test the yellow wire while the engine is cranking, connect the VM to the where it starts (ignition switch) and where it ends (at the solenoid). This tests for voltage drop (or loss of voltage due to excessive resistance) in that section between the test leads.

Whats adding to my confusion is the battery (brand new), with negative term disconnected, seems to drop down to 12.5 and below over a couple of days. Does this sound normal.

Thinking of attempting to set up some sort of bypass/remote start switch to see if that works and maybe help me narrow down the problem. Or throw in the towel and take it to a shop...not my preferred solution.