Cruise Control

[DMCJosh85]

After seeing another DeLorean with a cruise control setup at a recent meetup, I'm convinced that this is something I'd like to have. When looking at some of the parts needed on Amazon I found a user review that specifically and helpfully listed that the reviewer did this to a Manual 1981 DeLorean.

Anyway, the reviewer lists everything needed, provides helpful images but one thing is left a little vague at this point for me. It is mentioned that a total of 2, 5-pin relays will be needed if the car has LED brake lights. Perhaps this is answered in the installation manual for all I know. but I'm wondering if anyone has done this and could provide some clarity on why these relays are needed on account of LED brake lights, as well as where and how these were wired in to function.

In the event amazon ever makes my link above a dead link,m ill copy and paste what the reviewer posted here as well as include their images.

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See review here: https://www.amazon.com/Rostra-250-12...yword=delorean

Purchased:
250-1223 Universal Electronic Cruise Control
250-4165 Magnetic VSS Speed Pulse Generator Kit
250-4206 Universal Disengagement Clutch Switch
250-3592 Dash Mount Cruise Control Switch
Two 5 pin relay kits from NAPA.

Read the instructions multiple times. Wired everything up. Bent a custom bracket for the speed sensor and bolted it to the transmission. Pulled it out of the garage and was shocked to discover it was working on the first try. I've driven hundreds of miles with it and haven't had a problem. I believe the procedure in the manual to get into troubleshooting mode is incorrect. Check their website for an updated manual.

Notes:
This is not for the basic user. You will need an intermediate knowledge of DC circuits and should understand why each wire goes where it goes before you make the connection.
If you have LED brake lights you will need the AUX relay. The clutch safety needs to go to the purple wire, not the brake wire which is on the opposite side of the relay.
The orange external LED wire is only a couple inches long and is hidden under the tape in the harness.
I used the ring terminal on the cruise cable and attached it to the bottom of the nut that holds the throttle cable.
The module fits nicely to the driver side front of the engine compartment. I used one existing bolt and two screws to hold it in place.2.jpg1.jpg3.jpg4.jpg5.jpg

[FABombjoy]

Short answer: the cruise unit senses brake pedal activation via a circuit designed for filament bulbs. It just doesn't work through diodes.

So you set up a relay to close when brake is pressed, and the brake sense is tied to ground through that relay contacts.

[FABombjoy]

There is a tech note here that clarifies wiring, "LED Tail Lights Note"
https://www.rostra.com/support/

[Bitsyncmaster]

Like most alarm units the ECU is looking for a low voltage from the load bulbs when not powered on. The easy way to get that for the micro 5 volt logic is put put a pull up resistor to 5 volts and have a diode driven by the load. That gives the micro the logic of on or off.

The fix for that logic is to use an NPN transistor to turn that pullup to zero volts when the signal is above 8 volts.

So you can probably get away from using a relay with just adding a load resistor on a brake light.