Why voltage drop to starter? (1 Viewer)

[skidplate]

Been having intermittent starting problems for while. Good battery, good alternator, gear reduction starter, good grounds. will get that annoying single click at the starter solenoid on occasion. I'm only getting around 11.7 volts at the starter solenoid. I traced back to the ignition switch and only have that 11.7 volts to the switch. From where does the switch receive it's current? Ih8 electrical gremlins!

 

[middlecalf]

Without the motor running your only source of voltage anywhere is the battery (unless you have your cell phone plugged into an outlet, ). So 11.7 volts means your battery isn’t so good.

On a ‘63, the ignition switch gets its current from a BR wire that comes off the starter solenoid where the + battery cable connects. Don’t know about a ‘75, but probably something similar. Unless the wiring harness has been butchered.

Single clicks of starter solenoid has always been a good red flag for a waning battery (or starter).

 

[skidplate]

Sorry, should have stated 12.4 volts at the batt. 11.7 at the starter solenoid when in start position. Im not getting a full 12 volts at the ignition switch so no 12 volts from switch to starter. With engine running 13 plus v. at batt.

 

[1969FJ]

My bet it is the ignition switch. Sounds like the grounds thing is good. When you turn the ignition switch to start, sends full battery voltage to solenoid. How to test, turn ignition switch to on position, then immediately run wire from + battery to solenoid. Easiest is have wire ready so the ignition switch is not there long.

 

[fyton2v]

Still seems like your battery isn’t strong enough. But wow, the amount of electrical gremlins I had to find when I put my truck back together ... just wow. What I thought where good ground contacts, were not. What I thought was correct wiring at my fuse block, was not.

 

[middlecalf]

I’d start with the ground that goes from the starter mount bolt to the frame - redo contacts to make sure metal to metal contact and is of good size (gauge). Same with the - battery to engine block ground.

 

[skidplate]

69FJ, been there done that, yes starter works when jumped.
I welcome all suggestions.

 

[wooten]

Had a similar issue with mine that was solved by replacing the battery cables. Had too much voltage drop across the cable and inconsistent connection. It’s a 1979 so the circuit might be a little different.

 

[1969FJ]

69FJ, been there done that, yes starter works when jumped.
I welcome all suggestions.

Schematic, 1975. The only resistance is the ignition switch. Take a look. The 12 volts has to go through the switch to get to solenoid.

 

[Solace in Solitude]

I presume this is in reference to your ‘75 and the GRS worked before...

The “click” generally means low/dead battery, bad battery cable, dirty battery terminal-to-post connect, or bad/dirty grounds.

If all the above connections are clean and snug:

- Tap on the starter case and solenoid, with a screwdriver handle or a hammer.
- If it still won’t crank, jump the battery from another vehicle, a jump box or a generator.
- If it starts, have the battery checked again.
- If it doesn’t start, check your GRS wiring,
IIRC, the GRS requires only two wires.

Here’s a pertinent ‘75 schematic fragment, from @Coolerman’s site.

 

[fjc-man]

How many times do you think your 40 has been started in its lifetime? You have nothing to lose, replace the electrical portion of the ignition switch. Take the steering column clamshell off and one more screw, plug in the new one. Done.

 

[skidplate]

Appreciate the input. I've owned the truck since 1995. Ignition switch was replaced a couple of years ago, I'm on my 3rd starter , replaced the VR when I replaced the alternator a while ago, so I'm not on 1975 electronics. The guy I bought it from totally rebuilt the engine and drive train, and I've been very fortunate that I've driven nearly 75000 miles with only replacing normal wear items. This is the first time I've been skunked. Ih8 electricity!

 

[1969FJ]

Appreciate the input. I've owned the truck since 1995. Ignition switch was replaced a couple of years ago, I'm on my 3rd starter , replaced the VR when I replaced the alternator a while ago, so I'm not on 1975 electronics. The guy I bought it from totally rebuilt the engine and drive train, and I've been very fortunate that I've driven nearly 75000 miles with only replacing normal wear items. This is the first time I've been skunked. Ih8 electricity!

I get your frustration. But common sense prevails. If you put a multi meter on the solenoid , and, go to start , and read lower voltage than what the battery is, there is a drop. If you then direct drive 12 volts to solenoid, and it works as you have said, looking at schematic only thing in line is ignition switch. Now, if there is thoughts that a few years ago the switch was changed, AND, it cannot possibly have a problem, continue looking. My guess it is switch but I am only a contestant here so carry on.

 

[Steamer]

You mentioned “intermittent” and “on occasion” which can really hamper diagnosis. But if you are convinced that jumping the starter will work all the time, then that rules out the battery, cables, starter, and the frame grounds. How about running a temporary jumper from the battery +, to the battery terminal on the ignition switch to see if the lower voltage there is the problem.

 

[ibinazbass]

I dealt with issues like this for years with my '68. I replaced 2 or 3 starters in a period of 3 or 4 years when we first got her. What ultimately fixed it was installing a starter relay. There is a reason that cars now-a-days use relays for everything. Your ignition switch was designed, but has a hard time handling, all those high current loads. Ultimately it's having a hard time supplying the starter solenoid and the coil with enough voltage. The solution (a relay) is to use a low-current device to control a high current.

First off, I'd check the voltage drop of your positive battery cable while cranking. If that's no good the next portion doesn't work.

To install a starter relay any old 20 amp relay from the parts store will do, some even have a mounting bracket and pigtail. Run the wire from the ignition switch (that goes to the starter) in to pin 85 on the relay. Connect pin 86 to ground. Then take a new wire from the battery to pin 30 on they relay. Run another new wire from the pin 87 to the starter solenoid. Viola!

This schematic is a generic one for a headlight but works exactly the same. Also you can run 85 and 86 either way.

 

[Solace in Solitude]

I find this relay diagram/explanation easier

Have you checked your positive battery cable?

I’ve had cables look fine, but found a voltage drop, from one end to the other.

I cut them completely corroded inside the sheath.

 

[skidplate]

Thanks. Yes 12.5 volts from batt.. to starter, but 11.7 volts from ign. to starter solenoid. Going camping for a couple of days. Will attack this monster when I get back.

 

[Steamer]

Have you checked your positive battery cable?

I’ve had cables look fine, but found a voltage drop, from one end to the other.

I cut them completely corroded inside the sheath.

In the early 90’s I had this same problem with a brand-new cable on a Ford pickup. New battery and new cables. The bonded-on + battery lug had a bad connection inside that failed only under load. I had full battery voltage at the solenoid, but when I tried to crank, it dropped to only a few volts. Drove me nuts and I replaced a good starter before I figured it out. I’ve since learned how to do proper voltage drop tests which can quickly pin-point problems like this instead of playing the guessing and parts swap game.

Meters with a “Min/Max” function and alligator probe clips work great for voltage drop tests. There’s some good videos on YouTube vids explaining voltage drop testing. Some not so good also so one needs to sort through them. HTH

 

[skidplate]

I went ahead and added a relay, cheap, quick, easy, and it works. Thanks all for the help.

 

[Coolerman]

I see you solved this using a relay but the original issue still exists.

Something I did not see mentioned: What kind of shape is your fusible link in?

If you look at the schematic you will see that the power feed to the key switch is actually quite long. From the positive battery terminal to the fusible link, through the fusible link via about 7' of 10ga white wire to the amp meter, through the amp meter then through about 4' of 10ga White/Blue wire to a 12ga White/Blue wire spliced in the White/Blue alternator charge wire then finally up to the key switch. Now the wire itself is probably OK, but the fusible link has three places where the resistance can be quite high. The connection to the positive battery terminal, and the two connectors where it attaches between the battery and the main harness. Also the fusible link itself can degrade. It is only 14ga wire and if it is corroded it will have high resistance. I would pull the link out, inspect the link itself for broken wire or corrosion, and if it is good then clean the terminals in all 4 connector housings. I sell new links if you see that your had degraded.