Tachometer Problems
 

i have a 1971 2.2 liter with a marelli distributor and i have finally got the engine working but i have no tach signal. where does the signal come from, off the distributor?? if it does, where does that signal go and where does is come out and everything. i've checked my wiriing against the wiring diagrams from the service manuals and everything seems to check out so i don't know where to go from here. any help and insight would be great.

Joe
'70 911T 2.2, '71 motor

I had exactly the same problem on my 71 2.2L with the Marelli. I found that I was not getting a signal from the dizzy. As a test I linked up the signal wire to the 12volt terminal on the coil. I then found the tach worked but was reading way off. At idle the tach was reading about 6000 rpm. I then found the PO had been running a later tach with the 2.7 motor he had in it. I found a 71 tach and installed it. Works fine now. I'll check tonight when I get home at which wire goes where. I think it is the black and purple wire is the signal wire. It's been a while since I had the problem. PS I'll let Early S man weigh in on this one. He seems to be the resident tech expert I think.

Joe,

There should be two wires at the distributor points terminal ... Black goes to the CDI unit #9, and Black/Violet goes to the Speed Switch #11 -- in the diagram below, then on to the Tach, through both 14-pin connectors. If your Speed Switch [aka the Speed Relay] is still present and wired up the problem may be a dirty/corroded connection at one of the 14-pin connectors. If the Speed Relay has been discarded or disconnected ... that tach wire may have been disconnected!

Be very careful cleaning the 14-pin connector pins and sockets ... as they are silver-plated brass and fragile. No wire brushes or emory cloth, just an old toothbrush soaked/dipped in 91% isopropyl alcohol, followed by air drying. The pins of the 14-pin connector can be spread slightly with a Stanley or Exacto #11 knife blade.

You can test for a good signal at the Black/Violet wire at the tach with a 12 Volt test lamp connected to any +12 Volt source.

http://www.pelicanparts.com/911/911_...971_Part-2.jpg

is the speed switch a black little "micro switch" micro being 1" by 1/2" for 1970 with a toggle switch on it?? if it is, i have that removed, is there anyway to bypass that??

Joe,

The Speed Switch is an aluminum box approx. 3" x 2" x 1" with riveted steel mounting tab ... mounted on the electrical panel next to the Voltage regulator.