New to me. Tach & signals

[Don W.]

Last night coming home some weird electrical gremlins appeared. The tach started reacting to the turn signals. Don't laugh, it's true. It would jump 1000rpm in sinc with signals. Volts, both on the dash and on the digital readout on my inverter (to run the laptop) were only 11 or slightly below even with the lights off. Yet if I shut it off it starts right up as if nothing is wrong. If I stepped on it the tach would run all the way up to 8000rpm.

Anyhow underneath of the dash is apart again.(I've lost count:rotf Found one bad connection. Crimped term came apart with a slight tug. I've checked grounds. Did some meter reading, volts and ohms. Good there.

Right now it's a work in progress. Vacation coming up so you may not see results for a couple of weeks.

I suspect I can find it but thought if someone has something more that the usual "check grounds" I'd appreciate it. Just FYI I'll probably check grounds 2-3 time before this is done. I have the books and am researching there as well.

Thanks.

 

[DaveP]

Re: New to me. Tach & signals

The actual ground to check is the 10ga Black wire at the thermostat housing, or LF of the intake. That ground runs into the truck through C100 and supplies ground to all non-ecm related components inside the truck. Cluster, ash tray light, radio, glove box light, light switch (dome switch and panel dimmer), tone generator, turn signal flasher ground. There may be others, but that's all I can think of off the top of my head. If any of these also affect the tach, it may be the ground at the intake. If these others do not, then the problem is in the cluster, or AT the connector or pigtail to the cluster.


The power windows, door locks, cruise control, fog lights, ground to the pedal bracket. So these rely on the ground strap from the firewall to the block at the LH head.

So yes, "check the grounds", but the only one that matters is the one at the front of the intake.

 

[Don W.]

Re: New to me. Tach & signals

Yup, been there. One question I have is the ground "connector" above the steering shaft. Looking at the drawings it appears to have multiple push on connectors for whatever might go there or that I would add. I have yet to find the thing.

My other concern is the C100 pass through at the firewall and if there might be a bad connection there. I've had it apart before. Might just check it again.

Thanks.

 

[0966Sy]

Don, is it doing this consistently? I'd suggest getting to C101 over by the ECM. The female side has many inputs to the cluster. I'd start by getting out the wiring diagrams in the service manual. It will help you see how all those circuits in the cluster are related. You could start checking continuity across the cluster circuits from C101, you may just have a couple intermittently shorting to each other

 

[Don W.]

Re: New to me. Tach & signals

Don, is it doing this consistently? I'd suggest getting to C101 over by the ECM. The female side has many inputs to the cluster. I'd start by getting out the wiring diagrams in the service manual. It will help you see how all those circuits in the cluster are related. You could start checking continuity across the cluster circuits from C101, you may just have a couple intermittently shorting to each other

It's intermittent. Good plan though, I'll check it/them tomarrow.

Thanks.

 

[gstacky]

Re: New to me. Tach & signals

Yup, been there. One question I have is the ground "connector" above the steering shaft. Looking at the drawings it appears to have multiple push on connectors for whatever might go there or that I would add. I have yet to find the thing.

My other concern is the C100 pass through at the firewall and if there might be a bad connection there. I've had it apart before. Might just check it again.

Thanks.

There are 6 pins on this ground on the column, you have to be a contortionist to see it, but its on the left side of the column, bolts to the steel bracket that holds/supports the column, and can be reached by reaching your hand up to the left of the brake pedal. Each wire going to this is individual and has a little clip on the wire side to press to release it. Basically it's right behind the cluster, on the back side of the metal support, and would be right behind the speedo area.

 

[Don W.]

Re: New to me. Tach & signals

There are 6 pins on this ground on the column, you have to be a contortionist to see it, but its on the left side of the column, bolts to the steel bracket that holds/supports the column, and can be reached by reaching your hand up to the left of the brake pedal. Each wire going to this is individual and has a little clip on the wire side to press to release it. Basically it's right behind the cluster, on the back side of the metal support, and would be right behind the speedo area.

Thanks, sound like I need an extra joint between my wrist and elbow...

 

[DaveP]

Re: New to me. Tach & signals

One question I have is the ground "connector" above the steering shaft. Looking at the drawings it appears to have multiple push on connectors for whatever might go there or that I would add.

It's called "Ground Buss" on the diagrams. I called it the "grounds on the pedal bracket". And I described "what goes there" too. In the post directly above yours where you asked about it.

The power windows, door locks, cruise control, fog lights, ground to the pedal bracket. So these rely on the ground strap from the firewall to the block at the LH head.

 

[Don W.]

Re: New to me. Tach & signals

I knew what you were talking Dave. Just have never actually found the thing. I wanted to use it for a "master ground" for all the stuff I've added. Gauges, alky, etc.

 

[syclone809]

Re: New to me. Tach & signals

Thanks, sound like I need an extra joint between my wrist and elbow...

Probably better if you put it between your index finger and thumb

 

[Don W.]

Re: New to me. Tach & signals

Well I may have actually found the problem. Recall above I found the bad hot lead. Not thinking that really was it I continued. Heading 0966SY's advice I pulled the ECM. I have my PLX wide-band maneuvered up into the space between the ECM and the lower dash. Fits right in. So with all that on the pas floor I started going though everything. All of a sudden the ground wire from the 4 connector plug for the PLX is laying in the floor. Hmmm, now I'm getting somewhere.

Trouble is I can't get the terminal out of the PLX connector to replace the wire. Since I'm in no rush (vacation) I think I'll just get a hold of PLX and see if I can order that piece.

And I'm still gonna redo some of my grounds up to the aforementioned ground buss connector.

Thanks all.