Where's the resistor in the coil pink wire from ignition switch?

My new relay circuit for the new column is wired and ready to install.
It means cutting the OEM switch connector and using the new three relay circuit.

My question:

Where does the resistor live in the wiring harness for the coil pink wire circuit?

Is it in the wire?

Is it in the ignition module?

Is it within the switch I am deleting?

Or did GM hide the 1.35 Ohm resistor some place else?

The module has a heat sink... is it used to dissipate the heat while lowering the voltage to 9.9v during normal operation of the coil?

Just not sure if I need to buy a 10W 1.35 OHM resistor or if it's baked into the circuit someplace beyond the ignition switch.

Does the fuel gage act as the resistor when in drive mode and at reduced voltage vs the starter purple wire mode?

Ready to learn more every day!

It's the wire if my memory serves me right.

Yes and where specifically is it?

Between the ignition switch and the fuse box?

Between the box and the coil?


Memory working... YES Please!

If memeory serves,the hei doesnt use a resistor wire.it needs a full 12 volts

When it has a small body/cap HEI it has a separate coil.
The HEI with the coil in the distributor uses full 12V. IDK is it the same for the small cap HEI with external coil?
I think I add more confusion than anything else..

If you are talking about the resistor for the ignition, it was only used to reduce the running voltage for points ignition. It is not needed with electronic ignition.

If you see something inserted in your ‘87 harness it’s more likely to be a diode to prevent power feedback from one component to another.

RanchWelder said:

Yes and where specifically is it?

Between the ignition switch and the fuse box?

Between the box and the coil?


Memory working... YES Please!

Click to expand...

The wire itself is a resistance wire,the whole wire is the resistor . If you change the length,you change the resistance. GM hasn't used that since 1974. So if you are working on something 1975 or later there is no resistance in the coil power wire.

Yeah you're way off base here man. The small cap HEI, the efi distributor, uses a full voltage. The resistor wire was only for points.

Thanks for the input.

The AI algorithm states the resistance for the points distributor is 1.5 OHM, while the TBI system switches between full 12V during starter relay ignition, then switches back to the resistor to 1.35 OHMS. (NOT 1.5 ohms as in the ceramic resistor systems of the past).

It also says that if you operate the TBI without the correct ohm rating within the coil relay, specifically at 1.35 ohms, you will ruin the coil for the TBI during normal running operation when NOT starting. It specifies the coil requiring 9.9v to run during ECM control, not 12v.

So my research shows there's either bad information on the web or there's a secret lower ohm rating somewhere within the circuitry.

Thanks for your responses. If anyone else has a clue IE: Kieth... please chime in before I ruin my coil with my new home made relay circuit.

You guys and Girls Rock!

Easy enough to check. Backprobe the connector at the firewall check resistance to the coil terminal of your old harness. If it matches your resistance spec your information is true. If reads zero ohms,your information is incorrect. It is possible they went back to a resistance wire when they went to TBI and non of us got the message. As many of us have worked on these trucks though ,I'd sure think one of us would have caught it by now.

KEITH may answer you if you spell his name right????

OK, full 12v it is.

So much confusion on the internet.
Really appreciate Old Guy Bill, Ali-c20 and Craig Nedrow.

RanchWelder said:

Does the fuel gauge act as the resistor when in drive mode and at reduced voltage vs the starter purple wire mode?

Click to expand...

No, GM fuel gauges do not have a voltage regulator like some older brands. They have two coils inside on each side of the meter. Current through the coil creates a magnetic field that pulls the needle to that side. One coil is completed through the tank resister.

So even if the battery voltage varies, each coil gets the same voltage. On the back of the fuel gauge is a resistor. That resistor is the match for a tank sensor (resistor) which may have a deeper tank. (longer variable resistor). Example, 40 gallon tank verses a 20 gallon tank.

Coil resistance not tank fuel gauge resistance Turbo4whl... LOL

I'm sure I need that info just not yet... LOL!

My attempt ton increase the guage of the fuel electrical power circuit is still in the works because they routed like crazy people through the fuel pump and oil switch without defining where they break or change colors.

Luckily, I have not blown a fuse yet, sir~!