75 Power Wagon starter relay

[Kern Dog]

I call the NAPA store and the man asks...."Which engine?"
Uhhh....
Does it matter? I'll bet that it does not but the counter man with experience already knows and bypasses these questions.
I can't be hard on the guy...This is a 49 year old truck and he is maybe....25?

The truck has had a tendency to drain the battery over time. I'm not sure where the draw is. It is a basic rig...No auxiliary lights, gadgets or anything. The alternator and voltage radiator are working but two separate batteries drain down if I leave the cables connected. If I pull a cable, it holds a charge.
I'm limited on my knowledge of electrical issues but I'd think that there has to be some accessory that is leaking voltage. The brake lights don't stay on. The only thing pulling power at rest is the voltmeter gauge. Several years ago I did the Ammeter bypass and added a Voltmeter.
I use this rig to do dirty jobs out back....Tree and branch hauling, garbage and scrap hauling, pushing around the project cars, just work horse stuff. I've been cutting up some tree sections that fell from a storm last week and the truck is a great tool hauler. It starts and runs great.
Today I went to crank it and the key turned with zero response. It was like the battery was totally dead yet the VM gauge read 12 + volts.
I popped the hood and wiggled the battery terminals, then crossed the terminals on the relay...Boom! chuga chuga chuga...the sound of a 440 rumbling through generic Flowmasters!

Time for a new starter relay. I've had the truck since 2013 and I don't remember if I ever replaced this one before. I doubt that it is original.
I guess I'll see if the relay was somehow leaking voltage and draining the battery. Hopefully it will fix the "no start" problem at the very least.
Cheers!

 

[Kern Dog]

The truck starter relay is different than the car versions. I'm not sure why since the starting circuit is the same. Here is the car relay:

This next one is missing the spade for the neutral safety switch,

 

[Kern Dog]

The truck relay, this looks just like the one I bought.

These have mounting tabs on each side.
At the bottom of the relay, there are 2 spades. MY old relay only had the one on the left. Oddly, I didn't have any wiring going to the neutral safety switch on the transmission. The NSS terminals had a coat of greasy dirt on them indicating that there hadn't been any wiring there in awhile. This is odd because usually, if there is no signal from the NSS, there are no backup lights and the starter won't be engaged. The truck has always started fine when the battery is up. It had a 4 speed in it when I got it, I converted it to the 727 to make it easier to drive around the back yard. I either had it wired and it came off or it never had it and somehow still started without it.
You can get the starter to spin with no wiring from the NSS but you need to "ground" one spade on the relay, the one on the lower right.
Again, my old relay was missing that spade so it is a mystery as to how it started all this time.

 

[Kern Dog]

A guy at FABO that is a friend of mine (Who often chimes in to bail me out of a jam) popped in and set me straight.
4wd trucks with manual transmissions were originally fitted with slightly different starter relays. They lacked that spade at the lower right corner:

Instead, they had a flat metal section that attached the terminal to the case of the relay to ground it and complete the circuit. I didn't look real close at mine when I pulled it but there it is.
It seems like the new ones work fine but need that lower right spade sent to ground somewhere. A short wire to the fender liner should work.

 

[7mopar]

If it has a clock or radio with a memory. Either will drain the battery over time. That could take days, week or months depending on the power pull and the battery.

 

[Kern Dog]

There is no choke and an alternator cannot drain a battery when the engine isn't running.

 

[7mopar]

There is no choke and an alternator cannot drain a battery when the engine isn't running.

If it's bad it can on some vehicles. Hot wire and ground is all it takes. Alternator has both.

 

[69DodgeMan]

There is no choke and an alternator cannot drain a battery when the engine isn't running.

50 years of experience says your wrong.

I'll add my 60 years of experience and agree with Mr. Mopower.

You are WRONG Kern Dog, an alternator can easily be the problem you are describing. Shorted diode usually, and there are 6 of them to increase the odds. An alternator generates 3 phase AC power, the diodes rectify that AC into DC voltage, two diodes per phase. And yes, the two different starter relays are for an automatic or a manual trans. I would have expected you to have known that though.

 

[69DodgeMan]

Today I went to crank it and the key turned with zero response. It was like the battery was totally dead yet the VM gauge read 12 + volts.
I popped the hood and wiggled the battery terminals, then crossed the terminals on the relay...Boom! chuga chuga chuga...the sound of a 440 rumbling through generic Flowmasters!

Regardless of whether the alternator is causing your battery drain or not, this statement of yours would lead me to suspect either the ignition switch itself or wiring connections somewhere (likely at the bulkhead connectors). This is because your battery still had enough capacity to crank it over when you jumped across the starter relay terminals.

Not real sure on a '75 but on earlier cars, the starter relay had a yellow wire going to one of the small spades on the relay. This is the one that sends +12V from the ignition switch to activate the starter relay. You can either use a voltmeter to monitor the yellow wire for +12v when you turn the key to "start", or just use a jumper wire to put +12V on that terminal directly from the battery, that should crank the engine if the relay is working properly.

 

[Kern Dog]

I'll add my 60 years of experience and agree with Mr. Mopower.

You are WRONG Kern Dog, an alternator can easily be the problem you are describing. Shorted diode usually, and there are 6 of them to increase the odds. An alternator generates 3 phase AC power, the diodes rectify that AC into DC voltage, two diodes per phase. And yes, the two different starter relays are for an automatic or a manual trans. I would have expected you to have known that though.

I have never owned a vehicle that was originally built with a manual transmission prior to this one. This truck was owned by a guy that liked to tinker and do weird things to his vehicles. All sorts of stuff had been changed, added and substituted. You know, stupid old man gadgets and Harbor Freight quality accessories.
50 years, 60 years, I don't care. I am not a mechanic, I am a Mopar enthusiast that has owned upwards of 70 cars and trucks by now and I have never personally had an alternator discharge while sitting and then properly charge when running UNLESS this is the first one I've ever encountered.
Sure, you may be right. I'm just basing my responses on what I have experienced.

 

[Kern Dog]

Regardless of whether the alternator is causing your battery drain or not, this statement of yours would lead me to suspect either the ignition switch itself or wiring connections somewhere (likely at the bulkhead connectors). This is because your battery still had enough capacity to crank it over when you jumped across the starter relay terminals.

Not real sure on a '75 but on earlier cars, the starter relay had a yellow wire going to one of the small spades on the relay. This is the one that sends +12V from the ignition switch to activate the starter relay. You can either use a voltmeter to monitor the yellow wire for +12v when you turn the key to "start", or just use a jumper wire to put +12V on that terminal directly from the battery, that should crank the engine if the relay is working properly.

I'm familiar with the yellow wire. In my Charger, I had to ground it to allow the engine to start after I pulled the 727 and swapped in the Tremec 5 speed.