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More wiring than is needed, I think.
Posted by: Tom Turbo ()
Date: March 06, 2018 03:16PM

It all started with a disfuntional tach. I started chasing wiring for the tach thinking the brown wire is the negative coil feed wire and the black is 12 volts positive. Good ground confirmed with a meter. As you can see I have a petronix ignition unit, and that's where the confusion starts. I have checked the wiring scheme for the unit and nowhere does it mention 4 wires to the coil. The only way I can see to make the tach work is run a new wire from the negative side of the coil becasue the only wire on there goes to a Molex connector, and I can't see where the Molex goes to underneath the distributer.

One red wired from the coil goes to the resistor, the other red goes to the ignition unit. The yellow wires are a mystery, they go into the taped area which resembles a roach motel. I think a test wire to the tach for the brown side is the best solution but it seems kinda sloppy to have an extra out of place wire. Aside from surgery on the wiring loom and ideas?

If it don't go, chrome it!
Stroker McGurk, 1961.

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Re: More wiring than is needed, I think.
Posted by: American Mel ()
Date: March 06, 2018 03:19PM

That does not look like any Pertronix that I have ever seen.

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-----------------------------------------------
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
'66 Monza Coupe - 4spd, 140 Daily driver beater
'67 Monza Vert. - PG, 140 Daily driver beater

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Re: More wiring than is needed, I think.
Posted by: Tom Turbo ()
Date: March 06, 2018 03:29PM

How about a Crane XR-700? Sorry, my mistake

If it don't go, chrome it!
Stroker McGurk, 1961.

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Re: More wiring than is needed, I think.
Posted by: American Mel ()
Date: March 06, 2018 06:39PM

Does this help any?

> > Crane XR700 wiring < <

.
-----------------------------------------------
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
'66 Monza Coupe - 4spd, 140 Daily driver beater
'67 Monza Vert. - PG, 140 Daily driver beater

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Re: More wiring than is needed, I think.
Posted by: MattNall ()
Date: March 06, 2018 06:47PM

here's diagram





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Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: More wiring than is needed, I think.
Posted by: solo2r ()
Date: March 06, 2018 10:15PM

Take your balast resister out! Those units need full [switched] battery voltage! Tach should work on the neg side of coil. Also make sure the coil is compatible with this unit.
Does your tach have an adjustment for 4-6-8 cylinders?

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Re: More wiring than is needed, I think.
Posted by: 66vairman ()
Date: March 07, 2018 09:38AM

According to the instructions the XR-700 does require a ballast resistor with a stock type coil (1.2-1.5ohms). If your coil is a 3.0ohm then you don't need the ballast resistor.

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Re: More wiring than is needed, I think.
Posted by: Tom Turbo ()
Date: March 07, 2018 01:03PM

This is where the confusion started. The diagram shows 2 wires off the positive coil connection but it appears there may be 3 with the connection between the coil and resistor. It looks like some meter continuity testing may be in order.

Thanks for the help. I'll buy the coffee.

If it don't go, chrome it!
Stroker McGurk, 1961.

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Re: More wiring than is needed, I think.
Posted by: Seth Emerson ()
Date: March 07, 2018 01:09PM

From Crane:

TECH TIPS: BALLAST RESISTANCE

How can I tell if my vehicle has ballast resistance?
Here’s a quick test for ballast resistance. run the engine at fast idle and measure battery voltage using a volt meter. It
should be about 14 volts. Then measure the voltage at the COIL+ terminal. If there is a difference of more than 3 volts, a
ballast resistor is present.

When is a ballast resistor required?
A ballast resistor is required only with XR700 systems. Without proper ballast resistance, the XR700 and coil will overheat
and fail. All vehicles with original equipment points ignition are factory equipped with ballast resistance. This can be in the
form of a ceramic ballast resistor or a resistance wire between the ignition key and COIL- terminal. It can also be in the
form of internal resistance within the coil, such as Bosch® blue coils (typical on VW) and Lucas® coils found on older British
vehicles.

What do I need to do about ballast resistance when installing an XR700?
If the vehicle had points and you are keeping the original coil, you do not need to do anything else. If you are changing
coils and your vehicle has a ceramic ballast resistor or resistance wire, everything should still be OK. follow the coil installation
instructions.

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Re: More wiring than is needed, I think.
Posted by: Tom Turbo ()
Date: March 07, 2018 01:22PM

Electrically all is well, it's just the tach that is fershulgner. I hate to do it but I think a wire from the coil across the rear wiring loom thru the firewall and along the frame up to the tach brown is the best way. Simple but quick fix.

If it don't go, chrome it!
Stroker McGurk, 1961.

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Re: More wiring than is needed, I think.
Posted by: MattNall ()
Date: March 07, 2018 01:27PM

Have you "Wrung out" [ ohmmeter ] all the circuits at the Tack's head?





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: More wiring than is needed, I think.
Posted by: Tom Turbo ()
Date: March 10, 2018 09:17AM

I've been out trying to make the dash tach work this morningest using and extra tach.The plug to the tach has 12volts on the black so I hooked it to the 12v terminal and ran an outside wire to the other terminal and the coil negative. Nothing, tach is inop. If I take the tach to the engine compartment and hook up the necessary wires the tach works fine.It also dawned on me the coil negative only has one wire one it. That raises the question of does the tach feed wire operate off one of the Crane XR 700 wires.

The big question is if the tach works fine temporarily wired at the rear, but when I have 12volts from the connector in the dash (meter verified), a good ground, and an exterior feed line it is dead. Frustration!

If it don't go, chrome it!
Stroker McGurk, 1961.

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