Nothing Lasts Forever——Doghead Starter Relay

[Tinstar]

Last October I replaced my ignition switch after some troubleshooting. That switch is so fun to change. I first thought it was the DH relay. It was not.

Yesterday I was doing coyote patrol on the ranch and had stopped and started engine several times with long breaks in between.
No big deal.
When I tried to start truck to go home.....nothing.
No click, thunk or sizzle.
Everything else worked fine.
After checking battery connections, etc., I took screwdriver and jumped relay and drove home.

Assumed it was the ignition switch again as it was acting like before when it went out.
New ACDELCO ignition switch part installed and.....same thing. No start or anything.
Multimeter comes out and I start checking things.
Have 24v power to starter relay.
Ground good.
12v Power is applied to small terminal when switch is in start position.
Starter obviously works when relay jumped.

Conferred with another SS member who has way more experience with CUCVs than me and we both agreed that it’s the starter relay not being responsive to the 12v power and not internally completing connection for start sequence.

Bought new starter relay.
Same brand, model and specs.
Installed it and truck fired right up.

You can see in the pics the carbon buildup and arc pitting.
For whatever reason, the coil inside wasn’t energizing.
Who knows.
The relay was installed about 30 months ago and truck has been driven almost daily ever since. Lots of starts.

So they do fail eventually and will give you zero warning.
I’m good now for a while.

 

[Bighorn]

What resistance do you measure across the coil?
About 4 ohms would be right.
Is it open or shorted?
Those copper contactors look barely worn.
Either the plunger seized up and couldn't close the contacts or the coil shorted out or has lost continuity altogether.

 

[Tinstar]

Plunger was fine.
Coil gave up.

Will measure it tomorrow.
Curious myself.

 

[doghead]

The best part of the failure is that it failed safe(off).

 

[cucvrus]

Tinstar that surprised me to see you cut the harness as you always keep and want OEM stuff. You are in luck. I can send this with your parts order and revert back. While you were out looking for coyotes I was looking for kitty cats. Look at the pretty gray one I found. So sweet. Taste like chicken. Have a great day. No Marsupials were harmed in the making of this post.

 

[antennaclimber]

Your trouble shooting skills and your understanding on how the relay works in the start sequence got you back home. Being able to get the truck started with a screw driver shows that you understand how a 30+ year old truck works.

I agree with Doghead, Failing in the safe mode kept a bad situation from getting worse. Any component can fail no matter who makes it.

 

[Tinstar]

The best part of the failure is that it failed safe(off).

Exactly
Very thankful for that!!

 

[Tinstar]

Tinstar that surprised me to see you cut the harness as you always keep and want OEM stuff.

All original, with very few exceptions!
The DH modification being one of them.

The other is when I installed RPM, Water temp, trans temp and oil pressure gauges.

 

[Tinstar]

Your trouble shooting skills and your understanding on how the relay works in the start sequence got you back home. Being able to get the truck started with a screw driver shows that you understand how a 30+ year old truck works.

I agree with Doghead, Failing in the safe mode kept a bad situation from getting worse. Any component can fail no matter who makes it.

All the time spent reading posted info and old threads paid off.
Having another SS member to double check my thinking was a big help also.

Agree that no part is infallible.
They can and will fail at some point.

 

[tobyS]

You know if the screwdriver worked, then the coil did not fail. You are jumpering out the start switch and wire to provide electricity directly to the coil....which if it (coil) failed, would not pull in. I have the same condition on my 929 and carry a short piece of wire, having ruined a good screwdriver before. Mine happens about 1 time in 30.

 

[Tinstar]

The screwdriver made a direct connection between the large lugs.
The coil could have been completely gone and the screwdriver method would have worked.

Coil would not energize for whatever reason.
Screwdriver simply bypassed it

 

[URSATDX]

Can you explain, to me. what would have happened if it failed while not in safe (off) mode?

Thanks is advance.

The best part of the failure is that it failed safe(off).

 

[Bighorn]

Can you explain, to me. what would have happened if it failed while not in safe (off) mode?

Thanks is advance.

Starter runs on until it burns out or the batteries go dead or both.
Look up the Doghead starter relay modification here on Steel Soldiers.

 

[tobyS]

Can you explain, to me. what would have happened if it failed while not in safe (off) mode?

Thanks is advance.

See the spring....the spring pushes the contact bar away from the contacts. Springs deteriorate and contacts can weld themselves together, but his spring looks to be in good shape. He wasn't having a problem of not disconnecting the power, it was the engagement.

I too want to know as I have this very intermittent problem and carry a wire with me just for the purpose. My reasoning is that by going directly from the + starter terminal to the smaller coil makes mine work...thus the coil is not the problem...it's in the portion of the system I jumpered around...the switch or wiring. If changing it solved the OP problem, that's good. I may start looking for one, just to eliminate that possibility.

 

[Bighorn]

The 12 volt ignition switch sends 12 volts to the coil of the relay under the dash.
That relay sends 24 volts to the solenoid on the starter.
The solenoid applies 24 volts to the starter windings.
So you actually have a key switch, a relay, a solenoid, and a starter motor in the system with 12 and 24 volts.

 

[Tinstar]

What resistance do you measure across the coil?
About 4 ohms would be right.
Is it open or shorted?
Those copper contactors look barely worn.
Either the plunger seized up and couldn't close the contacts or the coil shorted out or has lost continuity altogether.

Checked coil today with Fluke Digital Multimeter.

Coil failed
Open circuit
zero ohm reading.

 

[Tinstar]

See the spring....the spring pushes the contact bar away from the contacts. Springs deteriorate and contacts can weld themselves together, but his spring looks to be in good shape. He wasn't having a problem of not disconnecting the power, it was the engagement.

I too want to know as I have this very intermittent problem and carry a wire with me just for the purpose. My reasoning is that by going directly from the + starter terminal to the smaller coil makes mine work...thus the coil is not the problem...it's in the portion of the system I jumpered around...the switch or wiring. If changing it solved the OP problem, that's good. I may start looking for one, just to eliminate that possibility.

The new relay completely solved the problem.
Truck starts as great as it did before.

It’s also a LOT easier to change than the ignition switch on top of steering column.