tach lead/pickup

[92 D/UNIT]

where can i find a tach lead(what is it called?) my tach is jumping all over the place and was trying to locate a new lead.
has someone experienced this? what was the fix?

[Begle1]

Are you talking the stock truck's pickup wires that are under the dash, or are you talking about an aftermarket's alternator pick-up?

I don't know where the stocker's probe is. But if you don't want to fix it, you can always buy the opposite model...

[92 D/UNIT]

i dont think its stock, it picks up a signal from the alternator. is there a factory pickup on my 92? if so where is it?

[DLittle]

Brian

If I remember right the tach lead is underdash by the hood release/ parking brake release. It's a flat 4 hole plug.

[Begle1]

The PCM equipped trucks have a tachometer pickup that ends someplace under the dash. It picks up a magnetic signal from the crankshaft someplace. The question is what year did the PCM's come out? I think that it was in 1991 along with the intercoolers...

Under which case the question is whether or not your aftermarket tachometer could hook up to the stock pickup.


Your tachometer is jumping around while your moving, right? They're supposed to jump around with the engine off because the alternator flux isn't enough to override interference from the grid heaters/ gauge lights/ radio/ etc. In any case, I'd definitely be careful to trace the wire from the probe to the gauge and make sure it isn't running against anything really electrical before I condemned the probe...

[Paccool]

The plug is a small flat plug and is located close to the steering column under the dash. The repair manual calls out "Near the fuse block". I think the plug is grey but can't remember for sure. There are 4 wires going to it -

Black -Ground
orange - Switched 12V
red - switched 12v to signal flasher(don't ask cause I don't know!! )
Gray - tach signal from the PCM

The crankshaft position sensor is where the signal originates and then goes to the PCM and on to the plug. You should be able to check for a reading at the gray wire with a digital meter. My PCM was bad and it took me a year to figure out what was going on. A new PCM solved the problem.

[92 D/UNIT]

Thanks for the info, ill see if i cant find it.

[RumbleFish]

The red is main power and the orange is illumination. You wouldn't necessarily have to hook it up to the flasher or whatever the manual says, just something that is hot only when the key is on.

[Paccool]

Thanks for the clarification Rumblefish. I suspected it was something like that but wasn't sure.I checked the leads when I was trying to figure out the problem I was having and didn't go any farther other than to see 12v on the orane and ed with the key on.