tach testing

[v8mgbal]

hello all, can you test a tach to see if it works without it being in a car. the reason I ask is when I bought my parts car it came with boxes of extra parts, some are 1500 and early spridget parts I think. so can it be done?

 

[jlaird]

So. hook it up with out putting it in the dash.

 

[v8mgbal]

ok, so how do I do that if its a diffrent year car or does that matter and thanks for the response.

 

[tosoutherncars]

Are the 1500s mechanical, or electric? If it's mechanical, you can chuck it up on a drill, and spin it to see if it reads...

 

[v8mgbal]

I think its electric.

 

[58Custom]

I will assume that the 1500 tach is an inductive tach like the 1275 tachs are.

If my assumption is correct, then all you have to do it put it in series with the positive lead to your coil and supply 12 volts to the 12 volt terminal and hook up a ground wire to the case. Start engine, marvel at you brilliance. The connectors for the unductive coil are the two bullet connectors. One is male, the other female. Now, I am not sure is direction of current will affect the tach. If so, just reverse them if the tach does not work initially. Anyways, the spade lug on the brownish PC board is for the 12 volts and a ground wire can be attached to any convenient bare metal part of the case but there should be another spade lug back there.

Hooking up stuff like this is easy for me but can be confusing for some folks. If I can see the circuit in my mind I can build it with test leads. I have built entire vacuum tube guitar amp circuits with test leads just to prove an idea.

 

[v8mgbal]

thanks Tom that's what I needed to know, will give it try tommorow. that seems so easy that now it sounds like a stupid question duh.

 

[dklawson]

The 1500 is probably using the same tach that the Spitfire 1500 ran. That's a later RVC type Smiths tach. It's voltage pulse sensing, not inductive.

Look at the front of the tach. If you find the letters "RVI" on the face, wire as Tom suggests.

If you find the face has the letters "RVC", there will only be one bullet connector on the back (and spades for power). The wiring for RVC tachs is very simple. Switched +12V goes in on the tach's spade lug on the insulator plate. The case of the gauge gets a ground connection. Run a single wire from the coil (-) terminal (dizzy connection side) to the bullet connector on the tach. Start the engine and hope it works.

Let us know what you find out.

 

[v8mgbal]

thanks Doug, I know I can get my questions answered here. what did we do before forum, oh that's right lot of trial and mostly error haha.