T-Series Tachometer and ignition switch

[GaryBeu]

OK...The full story/explaination would take a full page or about 30 minutes on the phone. So, I'll try to boil it down to the final question.

Tach has been dropping to zero frequently but a tap on the glass starts it back up. Today I heard a"pop" and white smoke shot out from under the passenger's side dash. Pulled over, turned off the key and the car just kept running. Found nothing~evident~under the hood or under the dash. I was afraid to pull the coil wire and not be able to restart so I drove her home 50 miles. As I started toward home I tapped the tach glass and nothing happened...tach is obviously not getting juice. Car starts with positive coil/tach wire hooked up but no tach working. Car won't start with this wire disconnected. What's up and what should I do next? Thanks. Sorry this is still so loooong!!

 

[GaryBeu]

I realize that I "should" have removed the tach whenI had to tap on it from time to time...but I put it off. It's out now and the black wire from it to the oil pressure gauge is fried/melted. Don't know why the smoke came out from under the passenger's side dash but... I'm going to replace that wire and see what happens next.

Seems like maybe everyone is just shaking their heads at my stupidity or some thing and not wanting to comment

 

[DrEntropy]

naaah.

Ya have a corroded ground circuit. Bad news is, ya gotta clean all the connections.

Sounds as if some power wire has grounded or met resistance.

 

[CZ_Dave]

Time to get a can of
Electrical Contact Cleaner.

This is a ritual that I do yearly.
always checking for frayed or burned wire,
making sure things are grounded properly

 

[DrEntropy]

If the smoke came from the passenger side, look to see if there is an abrasion in any wires near or touching the heater controls/cables.

 

[GaryBeu]

OK...the ground wire from the tach to the oil pressure gauge is fried in half. I have the square oil gauge between the tach and speedo. How in the world does that thing come out of the dash?! Obviously doesn't have the same fitting as the tach and speedo. I'm at a loss but it seems like it has to come out to get to the wires on the back. Thanks for any help.

Gary

 

[DrEntropy]

*bump*

If you let the smoke out of the harness, something likely has melted together to supply a constant current to the iggy circuit. Most likely place to check is where the main harness goes thru the bulkhead.

As for the square gauge, I really can't recall what retains it.

 

[Mickey Richaud]

*bump*

If you let the smoke out of the harness, something likely has melted together to supply a constant current to the iggy circuit. Most likely place to check is where the main harness goes thru the bulkhead.

As for the square gauge, I really can't recall what retains it.

Re: the oil pressure gauge - doesn't that have two studs and a bracket to hold it in?

Whatever the case, it requires itty bitty hands to get to!

 

[GaryBeu]

Mickey....Carla and figured that out. Her hand was actually small enough!! STILL haven't figured out why the key won't turn off the engine though.

 

[Mickey Richaud]

Mickey....Carla and figured that out. Her hand was actually small enough!! STILL haven't figured out why the key won't turn off the engine though.

Good deal!

Next time I need to pull the gauges, can I borrow Carla?

Electrical gremlins are the bane of LBC ownership. Usually due to ground issues, as already suggested above.

Say more about the key not shutting things down; not sure I follow that.

 

[GaryBeu]

Mickey...the tach was jumping on and off...normal rpm to zero and back. All of a sudden, it quit and a small puff of white smoke came from under the passenger-side dash. I pulled over, turned off the key and the engine kept running. I couldn't find an obvious problem so drove home. The black ground wire from tach to oil pressure gauge was fried in half. Replaced that. Car starts right up, tach works but, when I turn the key to "off" the engine keeps running. I have to pull the white (Positive) coil wire to shut it down. With the key "off" I have 12V to the brown only. With the key in "acc" I have 12V to brown and white/green. With the key in "run" (fuel pump working) I have 12V to brown, white/green, and white. At "start" I have 12V to those 3 plus a shot to white/red (solenoid). WhenI turn the key "off" and engine keeps running I STILL have 12V to the white. So...does that tell me it's the ignition switch? I'm lost.

 

[Mickey Richaud]

Based on that, my guess would be that the switch is bad. But why it isolates the white when in "Acc", but not after switching off has me stumped.

Does pulling the key out while it's running make any difference? Switching between "Off" and "Acc"?

Hopefully, someone else will jump in here.

 

[DrEntropy]

A "backfeed" from alternator circuit or a shorted pair in the harness is my WAG.

What does pulling the fuse in the green wire circuit (IIRC it's #3) do when the car is running with the iggy in "off"?

 

[GaryBeu]

Thanks Mickey and Doc...I just tried Mickey's suggestion first since it was easiest. When I turned the key off then back to "acc" the tach ~wiggled~ about 100rpm. I turned it to "run" then back to off and the engine died. Started it 5 times and it now works perfectly!!! WTH?? Healed itself?

Gary

 

[Mickey Richaud]

Dirty contacts and cams, maybe. Get some spray tuner cleaner and give it a few shots.

These cars need to be used; sitting for any time at all is their doom!

 

[DrEntropy]

Atrophy!

Glad it was as simple as that. CRC packages a great lube for electrical stuff, aerosol, "CRC 2-26". Find it at Home Depot in the house electrical department.

 

[GaryBeu]

I have CRC cleaner and actually used it on all these contacts. Maybe that helped. And Mickey...this car doesn't sit AT ALL. She normally gets driven everyday between 45 - 200 miles depeneding on if Carla takes her to school or I use her for work. We've "mostly" had a lot of fun with her!! Thanks guys.

Gary