couple electrical ?'s

[swankmetal]

couple of stumpers here. i've got a tach that will run off the stock sender, but i need to bypass all the stock wiring because it's shorted out somewhere. already blew up two $50 senders and i reeeeeally don't want to do it again. so if somebody could guide through this, i would appreciate it. i have found the harness and know what those wires are, but they disappear shortly after the harness and surface far, far away. so i guess what i'm wondering is what the wiring is at the disconnect by the radiator hose?? thanks



next question. i'm thinking about making a custom gauge panel and replacing my speedo with the tach. without the speedo hooked up, will the cruise still work? or is that where the signal comes from. thanks



dave

 

[DValentine]

Swank, I can't remeber what pin # the tac wire is, coming out of the box behind the battery. I think it is 53 or 47, and a blue and white wire. Its been a while since I looked at it. I was trying to do the same, before I was enlightened about TDR. I'll get in the books and find out for you. You might be able to run a wire from this to your cab to trigger your tac... .



Dave

 

[BHiggins]

The service manual has it as pin 43, and it's a grey and light blue wire. My manual is for 1992 but I doubt it changed for '93.



Hope this helps,

Brian

 

[swankmetal]

so this would be the wire that goes to the "sender" post on the tach, correct? i called cummins and they said that there shouldn't be any power going to the sender. at the connection by the front of the head, on of my wires has 11v, and one has 5v. think i'll just have to bypass the whole thing. thanks for the tips.



dave

 

[PToombs]

Just curious,where is the sender?And what does it read from?

 

[swankmetal]

the sender is right above the crank balancer, which is what it reads off. it's pretty hard to see but if you follow the wire that has a connector right at the front of the head, you should find it.

 

[PToombs]

I don't have a tach,so I was curious. It's on the wish list! thanks.

 

[swankmetal]

this is the one i got. hopefully it'll work.

 

[DValentine]

The 43 wire Brian is talking about is the one from the ecm to the cab. You should have wires under the dash, already plumbed in for a tac, if I am not mistaken. The crank sensor feeds the ecm, or so I think, and it is converted to a smaller voltage signal going to the cab. The crank sensor also has something to do with the alternator excitor... . or so I was told.



How else are you going to trigger the tac?

 

[Paychk]

The service manual has it as pin 43, and it's a grey and light blue wire. My manual is for 1992 but I doubt it changed for '93.



Hope this helps,

Brian

The 92 FSM I have; shows pin 43 as the distance sensor going to the transmission ??



The pin outs for the Tach sensor are listed as:



pin 4; ground Black/light blue strip

pin 7; 8 volts Tan/yellow strip

pin 24; tach sensor signal to PCM (computer)



The above pin outs are listed in the 93 FSM also, this is the connector at the PCM behind the battery



Quickie diagrams for the PCM can be found here:



https://www.turbodieselregister.com/user_gallery/displayalbum.php?&userid=5777&albumid=678

 

[Paychk]

The crank sensor also has something to do with the alternator excitor... . or so I was told.

PCM won't energize alternator until it gets a signal from the tach... I guess it doesn't want to waste electrons on the Alt. if the engine isn't running.

 

[PToombs]

Wow Swank, only $20 for a tach? If it works let me know, for $20 I might buy one anyways. I do have the crank sensor, funny I never noticed the wire before. The website said you can get a sender,but I didn't look, just added it to fav's for later. And yes the sensor tells the alt. to start charging, found that out the hard way on my '89, changed regulator, wasted hours trying to get it to charge, spinning it w/ my air wrench and the key on. (engine was apart)had alt. apart 3 times checking doides and stuff, when I started it, charge city,not like the 70's and 80's trucks.

 

[swankmetal]

yeah. i figured it was a good enough deal to give it a try. now i've just got a can o' worms.



so there isn't going to be a way to go directly from the sender to the tach? just wondering because the wires at the connection (at the front of the head) are giving me weird signals. i've actually got power to two of the leads, which the cummins tech said was not right (there should be two wires with varying resistance, and a ground. and in the cab, three of the four wires at the harness are grounded out with the ignition off, and two with it on????



not sure i buy the no tach/no charge thing though. i haven't had a sensor for about six months, and haven't had a dead battery??



anyway, thanks for the help guys. i'm needin' it.



dave



oh yeah, that website doesn't sell the sender. i called autometer industrial and the tech got a headache when i gave him the part #. actually, everybody i talked to almost laughed when i gave the part#. they said it was such an ancient part they couldn't really give me any info. techie said it should work with any "hall effect" type sensor though. we shall see.

 

[DValentine]

Swank, of the 4 wires in the cab, one is signal, one is power for the lights, and on a rheostat, one is ground and the other is keyed power for the tac. - I think this is correct. I can't remember what the colors are though. I'll have to look in my notes.



Your problem stumps me. I do know much more than what I have been told, about what the crank sensor is used for... the Alt. I never made sense to me, why would the Alt need to be told to produce power.

I don't know what the voltage should be on the wires at the plug. I don't think that is a Hall effect switch, though as it has power going to it. I can't explain how the crank sensor of ours works anyway. Are you going to try to figure out another type of "trigger"?

 

[swankmetal]

well, i just thought it would be easier in the long run to re-wire the whole set-up. i didn't realise that it went to the compruter though. i thought the three wires from the sender went directly to the under dash harness and they were just shorted out somewhere. i've got the harness wires listed somewhere, i'll have to check it out and see which ones were grounded and post back. thanks for the help though dave. much appreciated.



dave

 

[cerberusiam]

Dave, if you have no crank sensor and your battery is still charging there are 2 possiblities; its has been rewired to use an external alternator, or, your PCM is FUBAR. In order for a tach and charging system to work on the 92 models and up you must have a properly functioning crank sensor. The PCM could very well be messed up and that is why you are getting strange readings on different wires. The PCM handles alot of the grounding functions for components to work. Its tiny little mind may be really scrambled.

 

[swankmetal]

i was starting to wonder about that angle of things. is there a pass/fail test for the pcm?

 

[PToombs]

I can tell you that a Hall effect sensor creates its own signal from the teeth or tabs it is set over. They work best when set real close, like 1 mm. off the teeth. I hope you get this puppy working because I just ordered one today, but with the black bezel. If not it looks like we be workin' together for first genners everywhere! Sorry didn't mean to pressure you! :-laf If we have to we can put a Hall sensor underneath to read the flywheel teeth. We'll get er!

 

[DValentine]

I looked putting a sensor in the bell housing mounting plate in front of the flywheel. It would have to be tapped and needs to coriliate with the number of teeth on the flywheel itself.



Then I found TDR, and was SAVED.

 

[DValentine]

Swank, how is it coming with your electrical problems? I haven't come up with any solutions as of yet.