Dead tach #2

[DRD57]

When I put my coupe together back in '97 I bought the SW Wings mechanical 6 gauge set.  The electric tach lasted a year or 2 before it started reading erratically and not returning to zero when the engine was off. It now sits on my workbench at 5200 RPM's.

I complained to the SW reps at the Nationals in Louisville in 2000 and they agreed that those tachs were poorly designed but they said the newer version was redesigned and better. I had mine too long to get a no cost exchange though.

Last October, while readying the coupe for the Ego Rama, I bought a new SW Wings electric tach and put it in the car. Looked good, matched the other gauges and more improtantly it worked correctly. At least it did until I went to the March Meet. Somewhere on the 500 round trip I noticed the tach was reacting sluggishly. It was not keep ing up with the engine RPM and it doesn't go back to zero when the engine is off.

Last night I was reading the installation instructions for an MSD 6A and it mentioned something about unhooking the MSD (and tach) before doing any welding on the car.

I did do some welding on the coupe without unhooking the tach before the March Meet.

Did I kill my tach or are SW gauges junk, or both?

[rumrumm]

While I have not experienced this personally, I have heard of this happening, especially with cars with a lot of electronics. My welder buddy insists that you disconnect the battery before he welds on a car. This could be the source of your gauge problem.

[WZ JUNK]

I agree that you should unhook the battery before welding especially on anything with an MSD box.  It is a hard thing to remember to do but I have heard of many problems that might not have been had the battery been disconnected not only for welding but for any major electrical work.

Is your tach connected to the MSD box?  I just put a new tach in my drag car and when I hooked it up it as per the directions it did not work correctly.  I called Summit and the tech told me to hook it to the MSD box, I did and it works great.

[DRD57]

Is your tach connected to the MSD box?  

not yet, the MSD isn't installed in the car.

[C9]

A master battery switch in the + leg makes life easy for getting the electronics out of the picture when welding.

[DRD57]

A master battery switch in the + leg makes life easy for getting the electronics out of the picture when welding.

Good point! I have one of those and it was off while I was doing the welding. So does that mean I didn't kill the junk tach?

[Skip]

Well, you could use a surge suppressor on the battery.  MAC Tools has one in their catalog.  I believe Snap-On has one as well.  It's nothing more'n a big capacitor that bridges the battery terminals and adsorbs any spikes you might get from a high frequency welder.  It's a must for computer controlled engines.  You don't have to disconnect the battery and mess up the computer's memory when you work on a high-dollar car.  Resetting engine management computers and customer's radio pre-sets is a pain, especially when there's an alternative in your tool box.

As for the S-W tach, if it's a plastic-cased tach, it'll fail.  If it's a metal-bodied tach, it should be the re-designed unit.

I've sent back THREE of the plastic ones right out of the box.