Underdash wiring help w/gauges install

[9teen69]

Howdy, I swapped out my dummy gauge wiring harness with a gauge wiring harness. Won't start now. Not sure what I'm missing. Made no changes on engine side.

Also weird is when I screw in "relay" (circled red in pic) the horn sounds.
Where does the purple wire go?

1972 3 on tree truck without factory air, currently install vintage air though and will be converting to automatic in near future.

Installing gauge cluster with tach.

thanks

PS: just installed firewall cardboard...PITA especially around gas pedal

[ray_mcavoy]

Those purple wires go to the neutral safety switch and them being unplugged is most likely the reason why your truck won't start.

Your replacement harness must have came from a truck that had an automatic transmission. With a 3 on the tree, you won't have a neutral safety switch to plug those purple wires into. So until you get around to doing the auto trans conversion you mentioned, you'll have to temporarily jumper those two purple wires together. Once you do the conversion, simply plug that connector into the neutral safety switch on the auto trans column.

The horn relay is the part you have circled in red. Normally, the black wire leading to the steering column provides the switched ground to activate the relay (and sound the horn). It sounds like there is something wrong with your relay if screwing it to the firewall (grounding the case) makes the horn sound.

[9teen69]

ahh grasshopper...that's too easy and I'll also check my ground. I'll give it a try in the morning after my neck feels better Thanks!

One more question...What's the pigtail on the bottom of fuse block for?

[VetteVet]

I'm not sure what year GM started putting clutch safety switches in our trucks but you may have one on the clutch linkage or at the floor board that the pedal activates. I'm not sure how the purple wires plugged into it but look for a switch. You can jump between the purple wires for now but beware the truck will start in gear.

I don't recognize the pigtail, can you trace the wires?

[JointTech]

kind of looks like the one going to the dome/cargo lights.

[9teen69]

Thanks JointTech, it was the dome light, the wires are faded... looked yellow but were orange.

[9teen69]

Can someone take a picture of where the correct place to mount the two metal relays?

[9teen69]

More frustration , don't have any tail lights or brake lights. What am I missing, swapped out fuses.

[ray_mcavoy]

Originally Posted by VetteVet

I'm not sure what year GM started putting clutch safety switches in our trucks but you may have one on the clutch linkage or at the floor board that the pedal activates. I'm not sure how the purple wires plugged into it but look for a switch.

I think it was '73 in pickup trucks (GM cars had them earlier though). And in the 73-87 trucks, they were usually mounted to the left side of the pedal hanger bracket and used the same type of electrical connector as the auto trans NSS.

Originally Posted by 9teen69

Can someone take a picture of where the correct place to mount the two metal relays?

This is in my '72 ... not the best pic, but it shows the horn relay just off to the right of the fuse box.


The other relay (just barely visible at the top of the pic) is for the TCS (transmission controlled spark) emissions system. Unless you need it to pass emissions testing in your area, you can eliminate that TCS system and it's relay.

Originally Posted by 9teen69

More frustration , don't have any tail lights or brake lights. What am I missing, swapped out fuses.

Those are both fed from the "TAIL STOP PARK DOME" fuse. Start by using a test light or voltmeter to see if you have power on both sides of that fuse. It's not unusual to find a bit of corrosion on the fuse clips preventing them from making good contact with the fuse.

[9teen69]

Jumping the purple wires worked...truck starts.

Ray- thanks for the pic, knew I should have taken one before disassembly

I'll definitely clean them up and test tomorrow...thanks!

[9teen69]

Well I'm a dumb butt, I never plugged in the rear light plug. 3 days of chasing my tail

It was partially covered up because the POS firewall pad I got from Ecklers didn't have any cutout or scores for it or for the 72 gas pedal assy.

Thanks for the help!

[Custom/Ten]

Here is my horn relay not TCS above it but I do think I have a TCS relay on the other side of the firewall under the hood it's a 72 custom/10 3 on the tree 250 i6

[Custom/Ten]

I think this is a TCS relay ( not for sure) been researching it all day. like I said though its a custom/10.

[9teen69]

Custom/Ten - Thanks for the photos. Yeah its the TCS stuff, I know I don't need them but can't bring my self to cut them off, I just zip tied them and put them over in the fender well

[Custom/Ten]

Originally Posted by 9teen69

Custom/Ten - Thanks for the photos. Yeah its the TCS stuff, I know I don't need them but can't bring my self to cut them off, I just zip tied them and put them over in the fender well

Yea I had mine zip tied for a while too lol. It's hard to bring yourself to destroy factory equipment but I finally remove mine yesterday. Just remember that brown/white wire is hot if you leave it plugged in to the relay so be careful with it. I'm not afraid to admit my stupid mistakes, I just left that thing hanging for awhile without a cap, oops.

[chuchito]

Where does the TCS stuff connect to? Mine has a female plug on the other end. Where does that plug connect to and if it's factory, why can't I find it on the wiring diagrams?