Question: Why would there be a relay in the Starter Circuit?

[AussieCorvetteNut]

I have a question as I am working my way through a wiring tidy up and have come across an aftermarket relay that Circuit 6 (FSM 8A-31 - Pin 1F in C100) connects too.

It looks like the previous owners/ mechanics have installed a relay between the starter solenoid ciruit coming from the firewall plug and the starter solenoid.
The FSM wiring diagrams do not show a relay here, so I am curious why it is there.

Just wondering if anyone had any guess why they have done this.

I will check the layout on the relay and repost as soon as I take a look.

 

[dougelam]

Either it has/had a remote start system or a starter interrupt circuit for security.

The latter is pretty common in big cities!

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[AussieCorvetteNut]

Thanks, I will check that out

Either it has/had a remote start system or a starter interrupt circuit for security.

The latter is pretty common in big cities!

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I will check the other terminals on the relay out...sounds like this may have been the case.

I also found that there was a switch in the centre console that turned off the two injector pulses for the crossfire injection...while these are now removed, it was a pretty simple disable.



Tony

 

[hcbph]

Sounds like a form of battery cutoff to me. Most IMO would be on the negative cable but either would work. I've done something basically the same on mine, though it's on the negative cable so I can disconnect the battery when the car is not in use, prevents the possibility of an electrical short while in storage.

 

[AussieCorvetteNut]

Ok...here is is...

So the relay is a normally open (NO) double throw relay.

Terminals are:

86 Trigger wire is the factory purple ignition wire
85 Is and earth/ ground wire
30 Looks like a power feed - my guess is battery direct.
87 & 87A - Only one is used but I assume it actually feeds the starter solenoid.

So my guess is that there is no power to the starter solenoid until the ignition trigger flicks the relay, wouldn't this be like having two ignition switches that have the same result?

 

[dougelam]

A picture would help

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[Hot Rod Roy]

86 Trigger wire is the factory purple ignition wire
85 Is earth/ ground wire
30 Looks like a power feed - my guess is battery direct.
87 & 87A - Only one is used but I assume it actually feeds the starter solenoid.

If that wire is actually connected to 87 (not 87a) and goes to the starter solenoid, the PO was trying to assure that a full 12 v. is applied to the solenoid. He may have been fighting a hard starting situation and wanted to be sure there was a full 12 v. applied to the solenoid. That purple wire on pin 86 is the "start" circuit, not the "ignition" circuit. That wire on pin 87 would go to the old purple wire going to the solenoid that was cut to install the relay. Actually, not a bad idea, if the wire size on pin 30 is at least 5.0 mm (10 AWG) and the workmanship is good. Is the relay rated for at least 30 A?

(This info is from my '84 FSM, pg. 8A-31)

 

[AussieCorvetteNut]

Thanks Roy

If that wire is actually connected to 87 (not 87a) and goes to the starter solenoid, the PO was trying to assure that a full 12 v. is applied to the solenoid. He may have been fighting a hard starting situation and wanted to be sure there was a full 12 v. applied to the solenoid. That purple wire on pin 86 is the "start" circuit, not the "ignition" circuit. That wire on pin 87 would go to the old purple wire going to the solenoid that was cut to install the relay. Actually, not a bad idea, if the wire size on pin 30 is at least 5.0 mm (10 AWG) and the workmanship is good. Is the relay rated for at least 30 A?

(This info is from my '84 FSM, pg. 8A-31)

I didn't get a chance to take a happy snap on the weekend, I was busy with the cabin wiring for my FAST EFI install...
When they changed to RH drive and compliance for Australian Design Rules, they replace the two outer brake lights with amber lenses and convert them to indicator and hazard lights. What I found is that I had no back up lights and the reason was that they used that circuit as the brake light...ad
For registration it is required to pass a roadworthy and it will need back up lights or it will fail the test.

I only stumbled across it as I ran a new transmission back up circuit for my Tremec TKO Install (from C455 to the transmission tunnel via the FAST EFI harness, and back to C455), then I went to the tail section (rear bumper removed, I found that the green back up circuit was powering the brake lights...:ugh
They also had all the back up lights disconnected and bulbs removed (including the side b/ups).
That told me something was a miss. They also wired Pin P on the steering column plug (C144) to the back up circuit on C455...it pays to trace these wires.
Anyway, I have a solution for that mess, I am re-establishing the back up to C455 and C124, disconnecting their white Pin P wire on C144, then running a blue wire from the brake switch to C124 (there is a spare pin on this pigtail, well the blue brake light goes to this but there isn't a wire on the opposing side...so I will put a pack-con pin in and we are all good), then I will run a blue wire through the car to the rear tail lights with the existing harness...this will be connected to the brake lights.

Now, the starter relay...
I am pretty sure that Greg the previous owner did say that he was chasing a battery drain issue, so this may have been one of the solutions he put in trying to improve starting...it makes sense.

The relay is on the LH side of the car where the bulk head plug is now, so I was asking if anyone knew what it may be so I can relocate the relay to the RH side under the brake booster (remember it is RH drive).
I might re-install it now.

 

[Hot Rod Roy]

I might re-install it now.

If you've got to do that much work, I'd skip it! That relay shouldn't be necessary, if your other ignition and start circuit wiring is good, and your ignition switch and security relay are good. With RHD, your wiring to the starter might be shorter than these LHD cars! (Assuming your RHD wiring doesn't snake all over the car to pick up the original LHD wiring!) Are you using the original thru-firewall connector?

 

[AussieCorvetteNut]

Yes, but the firewall is changed during the RH drive Conversion

Are you using the original thru-firewall connector?

The engineering company that does a lot of RH Drive conversions here in Australia, removed the original firewall on the C4's during conversion...C5 and C6's all have the body conpletely removed...I believe that the C7 is the same...thats why it costs $60K AUD to convert to RH Drive...all the later generations have better conversion parts now that technologies have improved.
They engineered a mirror (well nearly) RH drive firewall and move the LH located stuff to the RH side and RH located stuff to the LH side.

The thru-firewall connector (C100 & C115) are still used but on the LH side with the a/c evaporator and heater, blower motor and washer bottle.
The RH side now houses the battery, brake booster and brake master cylinder, clutch master cylinder and of course steering shaft through to a RH steering rack...what brand of rack is unknown, but when I had it rebuilt, it was a combination mostly SAAB. There is a company in Canada that actually engineered these for the Engineering shop here in Australia.

The wire will be run around the front of the air dam and back to the starter mounted on the LH side.

I could run it via the k-member, but I had a harness running there and one across the rear of the engine and over time with heat, oils, fuels and road grime, the convoluted tubing and harness wrap becomes brittle and breaks, especially the convoluted tubing.

I know it is a bit of work re-routing the wiring, but its a lot more tidy.
I have also centralised the engine bay relays (except the front headlamps) and any inline fuses will now be in a GM type fuse holder. I made a special plate to mount on the RH chassis rail, that uses the factory fuel filter bolts, that houses the fuse block, relay block, 6AN fuel filter and FAST EFI fuel pressure sensor block.
FAST have four fuses and a relay in the MPFI harness I haved installed, that are in the wrong area and will most probably rub on the RH header...they are being moved to under the brake booster near the battery...its the only real estate I have left.

I took a Random Day Off yesterday and spent 12 hours pulling the real tail lamp harness out, unwrapping the harness wrap, running a brake light wire and resoldering and heat shrinking the circuits.
I tested plug C124 by running a wire from the positive terminal to this block as the earth strap is already installed. All the rear lights now work the way I want them to work, so I also spent most of the day working my way through the dash harness and cross-referencing it with the FSM wiring diagrams...all good.

I photo-copied all the colour wiring diagrams (well scanned them to file) and then re-printed them and bound them, so now I can write notes all over these and not wreck a 32 year old book. Where I have made changes, I have written these into the copied diagrams. Also made notes on what has been electrically disabled...ie cut then sealed with heat shrink or terminals removed from the connectors.

My build is:
Will the Edelbrock Pro Fo XT fit under an 84 Hood?