How do you wire a Tachometer?

[larry47us]

The tach on my 73E had a light that worked when I first picked Kermit up, but the tach didn't. So Mike swapped a wire (so he said) and the tach worked but then the light didn't. He said that I should pull the tach, and connect a wire between the two posts in the back.

Well, I finally pulled the tach, and when I saw what the back looked like, I was more confused than ever. There was this blue wire connected to a ground screw, but the spade plug was just hanging in the air. The plastic terminal at the bottom has an open slot, but there is no connector on it, and I don't see a picture in the Porsche Service Manual.

Any help is appreciated.

larry

[larry47us]

I figured out that the wire hanging there is a ground, and it needs to be hooked to Chassis ground. If I touch the spade plug to the case of the Oil Gauge, the tach lights up. If I touch the case of the Tach to the metal of the steering wheel, the tach lights up.

Is there some "standard" place that this spade plug is supposed to go? Or should I just stretch a wire from the case of the oil gauge to the case of the tach?

larry

[Steve@Rennsport]

Hi Larry:

Indeed, that IS a ground and you might have already figured that all of the factory ground wires are brown in color to aid identification.

The factory grounded the tach from a major ground stud on the chassis behind the instrument panel to the tach, then to the speedo case, then to the clock and then to the glovebox lamp ground wire.

Since all of these instruments are mounted in rubber, you need to attach that wire to a good, clean chassis ground for reliability.

[larry47us]

Steve:

Thanks for the input. BTW, have heard great things about you from Paul Donkin and from Stephan Wilkinson of "Gold-Plated Porsche" fame.

What I finally did was ground the Tach to the male spade plug on the back of the Oil Gauge. There was this male spade plug just welded to the case and I went to Home Depot and grabbed a piece of Blue wire (to match the one that was already there) and a small box of female spade plugs. Snip/snap, and 6 inches of wire did the trick.

Obviously when Mike put the car together, he didn't get the wiring thing. The car has a great body, and is pretty clean overall, but there are little things like this that don't work. Now that I have this fixed, and understand a bit more about the wiring, I will have to tackle the other two small electrical things that are annoying me -- 1. The dome light doesn't go on when the doors open; 2. The Glove Box light doesn't go on when you open the glove box. Your comment

The factory grounded the tach from a major ground stud on the chassis behind the instrument panel to the tach, then to the speedo case, then to the clock and then to the glovebox lamp ground wire.

gives me a track to go along. I know that the oil gauge is grounded to chassis, as is the speedo and the clock. I may just pick up some brown wire, and wire across from the Oil Gauge to the Tach all the way to the glove box light. Maybe that's why it's not working.

BTW, I am having my suspension inspected in the next few weeks, maybe I'll drop you a line for a bit of advice when I find out what, if anything, needs to be done. Kermit needs an alignment badly, but due to the cost, I want to find out what else needs doing before I pop for that expense.

thanks again.

larry

[Cornpanzer]

Larry,
Somewhere on this site is a nice PDF file of the electriacl diagram that has helped me with my car. Its still a rats nest under the dash tho

[larry47us]

Dave:

Thanks. I have a set of service manuals, complete with wiring diagram. I only need to figure out where the blue line goes??

Honestly, I would be better off with just a photo of the way things are supposed to look. I've got this hooked up, so I am working OK.

larry

[HarryD]

BTW, I am having my suspension inspected in the next few weeks, maybe I'll drop you a line for a bit of advice when I find out what, if anything, needs to be done. Kermit needs an alignment badly, but due to the cost, I want to find out what else needs doing before I pop for that expense.

thanks again.

larry

Larry,

I refreshed my suspension (shocks and rear springplate bushes) this winter and the difference is like night and day. Steve helped me with part selections and I had Rothsport (local for me) do the suspension tuning. Well worth the cost.

Did Mike replace any of the suspension busihings?

[larry47us]

Harry:

Have an appointment to have Kermit's hip flexors examined this weekend. We'll see what goes. Mike did absolutely nothing to the suspension. But, that wasn't part of the contract, and I really didn't want to throw extra money at the project last year, to say nothing about the time delay. But I knew that I wanted the suspension examined.

He said that the suspension was fine, but then again, it really needed an alignment, which he didn't give it. Actually, the PPI didn't reveal that either, so I'm a bit non-plussed by that. So, I'll just wait for Saturday. Honestly, I am extremely pleased with what Mike did with the car, the paint job, and the overall quality of the work and car. This wasn't a frame up restore, it was just a bare metal paint job that just grew. Mike is clearly talented. But, this project got a bit long in the tooth for what I paid him, and he wanted to end it with our prior agreements. That was really fine with me.

larry

[caproader]

Larry,

re the glove box light: Are you aware that there is a 3 position switch next to the light that determines when it comes on? It may be that your switch is verklempt.

On the dome light, you might want to check the door switches at the leading eadge of the door. As I remember, they provide ground when the door is opened and remove ground when the door is closed.

Looking forward to seeing you in Chicago next month.

John aka, the capitalist roader

[larry47us]

John:

Thanks for the advice. I am aware that the dome light and the glovebox light are both 3 position lights. And, thank goodness, they all work. I need to check the switches at the box and the doors to make sure that they work. Maybe that's my problem.

Also, the door switches don't have the rubber covers. Another of those little things that I need to work on.

It will be nice to meet you after all this time. Hope the weather holds out for the game that afternoon.

larry