Tachometer question

[spider2081]

I think the wires are soldered on the your ignition switch. After I unsolder the wires I use a dremel type tool with a small burr tool to clean off any remaining solder from the terminals. If any solder is on the terminal ends they will not pass through the bakelite casting that holds them. I also use the burr to grind off the head of the hollow rivets holding the 2 halves of the switch together.

[sigkadetm]

Installed new rectifier in alternator and I still get 31.5 volts ac. Took alternator to get tested and it tested fine. The person testing my alternator told me that some digital voltmeters will not read ac volts the correct way when testing an alternator. I may need to put a .5 microfarad 200 vdc capacitor in series when using meter. He said if there was a problem the idiot light would be on. So I am back to square one. Lights, radio, heater all run without putting any strain on electrical system. Next is the ignition switch.....this has to be the problem.

[spider2081]

Installed new rectifier in alternator and I still get 31.5 volts ac.

Interesting the reading seemed way too high. Usually when a diode is open the meter reads something between 5 and 15 volts AC. As I mentioned earlier I thought the meter might be displaying milli volts. Putting the capacitor in series with the meter should block the DC component of the voltage you are measuring an pass the AC to be measured. Do you have another volt meter to try???

The power to the coil pack comes from the pink wire on the ignition switch and goes to the Bat or + terminal on the coil. The D or - terminal of the coil has the 2 brown/white wires. One of these wires is the signal to the fuel injection computer the other is the signal for the tachometer. It is strange that the car runs fine and the tachometer does not as their signals are taken from the same point.

[sigkadetm]

I'm going to try and put the original alternator back in and take another reading this has got me stumped too because I did try two volt meters. The alternator that is reading wrong was from a 1992 Ford Tempo 95amp and I just put in a new rectifier. Strange all three of the same alternators would all read the same. On my coil there is a brown/white wire for the tachometer and a shielded wire that I assume goes to the ECU. When I gently push up on the wires behind the ignition switch the tachometer reads normal crazy.....I'll let you know how the tests go today.

[sigkadetm]

OK.....just put the old original alternator in and my meter reads 30.1 volts. Then I checked my Chevy traverse and I got 30.8 volts. My neighbor was outside and I checked his 2016 corvette and we got 30.2 volts so it must be the meter. Going to put the 95 amp alternator back in.

[spider2081]

No one can say you are not trying all possibilities. Are both volt meters that you tried the same brand by chance??

[sigkadetm]

One is a cheap CenTech and the other is a more expensive centech from harbor freight.

[spider2081]

I have one of Harbor Freight's cheap meters I got free with a coupon. I will try it today and let you know what it reads. Pretty sure its a CenTech.

[spider2081]

To my surprise I found another CenTec meter in the tool box. So I had 2 of them. I tested both of them on our 500L measuring the AC voltage at the battery. Both meters indicated slightly over 30 volts AC. One was 30.1 and one was 30.4. The meter I usually use is a 40 year old Kelvin digital meter. I have been using it almost daily up about 2 years ago when I retired. Now I use it weekly. It is not auto ranging. So I measured the AC with it and it would only flicker .01 on the 2 volt scale.
I guess that old saying "You get what you pay for" holds true. If my memory is correct I paid about $70 FOR THE Kelvin meter when I bought it.
I apologize for any confusion I caused you trying to help. The CenTec meters can not be used to measure the AC component of an alternators output.

[sigkadetm]

No problem. I now know for sure that I have a very good 95amp alternator in my fiat. Now lets see what happens when I conquer the ignition switch lol.....

[sigkadetm]

Well I did the ignition switch fix and the Tachometer is still not responding correctly. It only responds when I rev up the engine. It seems to get better when the engine warms up all the way.