[Dave R]

I’m trying to diagnose a no start on a 73 Formula and noticed a clicking noise coming from a relay on the firewall. I don’t remember seeing one of these before and was wondering what years/engines they were used on. It has a 350 with 2bbl, originally from California. Just about to start looking for a replacement as the clicking has now stopped.

[Formulabruce]

Guessing this is a late emissions bird. Dark blue paint. I think this is an emissions relay that controls a start up vacuum to dist. I'm not 100% on this but have seen one before.

[Dave R]

Yes, it’s 04 C build date (4th week March?). Wires are black and yellow black disappearing into the engine harness. Going out to try tracing them.

[Dave R]

I cleaned it up looking for a part number and found Littlefuse Inc stamped on it. Here’s a picture.

[Formulabruce]

Looks like a 1st gen Power Top fuse too.

[cnc]

I have the same on my 73, no clue what it’s for…

[Dave R]

Originally Posted by cnc

I have the same on my 73, no clue what it’s for…

I think it may step down the voltage. Wire in is larger gauge than the wire out. Mine has a reading of 40 ohms and weirdly both wires have key on voltage of 16 volts. Clearly I have electrical gremlins going on.

[rbrtmchl]

I have the same part on my '74. I believe this part of the emissions control system, Transmission Controlled Spark System, that on my car was removed some time ago.

The stock Start-up Relay Switch is mounted on the firewall. Blue and yellow wires run to a bundled set of wires. There is a connector with a blue wire and yellow wire near the driver’s side of the carburetor, but it is not connected to anything. The original Distributor Vacuum Advance Solenoid was removed at some point in this car’s history. Based on other posts on this forum, the general consensus seems to be that you are better off with this system disabled or removed.

[Shiny]

I have no clue what it is, but wouldn't a relay have 3 leads? I'm thinking power in, power out, and a "switch" in addition to the ground. I also agree a relay with two different wire sizes isn't expected.

As to voltage dropping, maybe current dropping (ie a power resistor) but doesn't appear the case is made to dissipate heat.

And yes, measuring 16V is unexpected... OK, Gremlin-ish.

Is this measured from the wires to ground?

Good luck and hope somebody can tell you what it is!

[Shiny]

I guess if it was a relay, it could be grounding the large wire and not feeding power to it. If this was the case, the small wire would be the "switch" (ie from a sensor or remote switch) and the big wire is handling current from something "needy", like a solenoid or other power hog.

If this guess is close to true, then clicking could be caused by the relay being bad, the ground contact being poor, or the device that is switching this relay acting flaky.

[Held for Ransom]

http://www.pontiacpower.org/pdf/74ponticemissions.pdf

Start up relay switch. Used in '73-5. Part number 6270698. 2 designs (manufacturers). LittelFuse will have the date code. Other will have the GM PN.

[Shiny]

Wow, what a great reference!

[Dave R]

Thanks! That helps a lot! Now I know what it’s doing, I should be able to figure out where the issue is.

[fbody_mike]

So based on the schematic and text, it provides 20 seconds of ground to the dark blue wire on key on, which lets the solenoids provide vacuum to the other emissions devices. Then when the engine is up to operating temp the temp switch will then ground to provide vacuum. Interesting. I don't remember seeing this on my 74. I guess someone tossed it long before I got that car.