87 Suburban electrical (IGN) problem

[mrwhite2you]

Also posed in the 73-91 Chevrolet and GMC suburbans group... as I thought about it, this is probably relevant to anyone with an 87... Apologies in advance for the cross-post.

I recently purchased an 87 suburban in fairly good condition (texas truck). When I was looking at it, the fellow I bought it from commented that he had hooked up a Sunpro tach on it, and when he hooked it up, there was a loose wire under the dash that if bumped, would cause the truck to stumble and/or die. Well, he was right, over the weekend I was picking up a couch and hit a bump in the road, and started getting a stumble. When I pulled over and started fiddling with it, she died and wouldn't restart.

After sticking my head under the dash by the fuse panel, I found what I thought to be the culprit. There was a red wire with a crimp connector (not spade, but the one that has 2 prongs) loosely stuck in the fuse block. I played around with it and if wiggled in just the right spot, the truck would run. Now this wire is stuck in to what appears to be where a fuse would go, so when I got home I went to replace this with a fuse, but it would not go in as there is a plastic tab between the two terminals. I believe this connector is above the 20Amp ignition circuit, and below two individual wires in plastic retainers.

I have a few theories as to what is happening. first, the two terminals that I am looking at are two seperate circuits to be used for accessory connections, and one of the connections does not work. Therefore, connecting the two together completes the circuit. Or, perhaps there is a circuit breaker that is supposed to be connected there, that the previous owner removed to install this tach, and did a real mickey mouse job on it. And thirdly (long shot) this wire being connected is actually completing the circuit to the HEI allowing the truck to run.

To throw one more wrench into the system... this truck was purchased from Houston area, and has a Ravelco (sp) anti-theft unit on it, where you must insert a specific key to get the vehicle to start. This unit has been (supposedly) disabled, but I am beginning to wonder if perhaps the wiring has just been rigged behind the scenes.

When I got the truck, I didn't receive the owners manual with it, and the Haynes manual that I have does not prove to have any helpful information. I am going to try to get into our local library this weekend, but was hoping someone would be able to provide either a photo/schematic of the fuse box under the dash, and/or a wiring diagram so I can attempt to dig into this. Also, any suggestions would be greatly appreciated.

Thanks!
-Mike

[swervin ervin]

Looks as though they used the spade terminal to hook up the alarm. The place in the fuse panel you speak of is not for fuses, but places to hook up to a power source, either ign, or bat. In other words switched, or full power all the time even with the switch off. It sounds to me like the anti-theft device is still hooked up and using the wire that keeps coming loose.

If you don't want the device, I would trace down the wiring and find out which wire it is. I would say it's tied into the coil power wire somewhere. I think a lot of the anti-theft devices are wired so the engine won't start unless a certain key or other switch is on. I also think some work on the starting circuit too. I would bet money yours is wired into the coil power circuit.

[mrwhite2you]

Mike, thanks for your reply... I kind of figured those terminals were used for accessories. I took another peek under the dash last night and found a few more interesting things.

First, the anti-theft device I was speaking of isn't an alarm, it is actually a cut-off (kill) switch that uses a special key to allow the vehicle to start. I don't have the key for it, and have been able to start the vehicle, which led me to believe it was disabled. The PO (who is the 3rd, at least) said it (anti-theft) was not hooked up when he bought it either. The PO was also the one who installed the tach.

I looked at some of the other posts here and found some good pictures of column wiring at http://67-72chevytrucks.com/vboard/s...threadid=52926 and if the labeling of the NSS is correct, then mine is disconnected and hanging next to the column.

The red wire connected to the accessories does follow the white one also wired in to the fuse panel, and both follow up to the tach mounted on the column. This red wire does not have a spade, but a 2 prong crimp connector. The truck will only start if the crimp connector is firmly installed and touching *both* of the accessory power terminals.

Time to break out the test light... and get that dang anti-theft device out.

[mrwhite2you]

Well, after playing around this weekend, I was able to figure out what was going on under the dash... Please forgive me if my descriptions are vague or I use the incorrect terms, I'm just getting started with articulating my issues/solutions. Only one way to get better at it, right?

Remembering that the "anti theft" device is used to kill 2 circuits, and based on the documentation I found on the web, it is usually used for ignition and fuel pump. I followed the armoured cable through the firewall and found where it ended. 4 wires, with red crimp-on butt connectors. Okay, so I can take that out of the equasion. I'm probably going to leave it installed on the dash... perhaps it will make a theif think twice about trying to steal.

Ok, looking at the fuse panel, there is a grouping of fuses at the bottom, with 2 jumpers (labeled 'shunt') installed about 1/2 way up on the left 2 "columns" of fuses, then the individual terminals for feeding accessories. the shunts have power on both sides, and taking a test light to each terminal above the shunts yields power on both terminals. removing the shunt causes 1/2 of the terminals to "lose" power, as the shunt is working as a jumper.

Well, I only have one shunt in the left most space, and the space next to it has a crimp terminal with the two prongs (not sure of the proper name, but it's the one that looks like a C that could go under a bolt or screw) that is connecting the circuit. So, this terminal essentially is taking the place of the shunt, and is responsible for powering the right 1/2 of the terminal accessories above it. On that right side, there is a factory accessory plug (gray wire) with a green wire taped onto it about 4 inches up. Following this green wire through the firewall, I discover it is wired in to the factory wiring, and follow this back to power the fuel pump. I verified this by turning the key on with the wire connected, and heard the whirr of the pump. Disconnecting this wire caused the whirr to stop.

okay, my deductions thus far are, the PO before the PO had a problem with the fuel pump not functioning, so he removed the anti-theft device. Then, discovered that it was the factory wiring that was the issue, and connected a seperate circuit to power the fuel pump. The only issue I can see with this 'design' of his is that if that wire ever were to short out, there is no fuse to protect it.

Then the PO before me removed the shunt to install the tach using the crimp on terminal attached to the tach power wire in place of the shunt. Unfortunately, the red crimp on fork terminal does not have the proper span between connections to make a good fit where the shunt was. Therefore, after a couple of good bumps, the wire knocked out of place, causing the power to the fuel pump to shut off, and the truck to die.

Solution: (temporary)

Where the shunt was installed, I put in a 20A fuse (I know, probably more than the fuel pump needs, but it's a start) that I ground down the plastic between the two terminals to allow it to fit where the shunt belongs. The power wire for the tach (which is what was connected to the wire/terminal that the PO used to replace the shunt) I crimped a spade terminal and connected it to an open switched power location on the fuse panel.

Solution: (permanent, in the future)

I tried going to AutoZone and Checker to buy a shunt. Wouldn't ya know, even though Littelfuse makes these things, you can't buy them with fuses. So, off to the dealer I went. He couldn't find them, sent me to the local boneyard. Local boneyard might have them, but it's a $25 yard charge for them to go out and get it. So, a $0.25 piece of plastic an metal, is really worth about $25 here! I will need to take a drive to a "you-pick" yard, of which the closest one is about an hour a way, and only open while I'm at work. Guess I'll need to take a long lunch.

If anyone has an extra one of these things (shunts) laying around, PLEASE let me know, you could save me quite a bit of aggrivation.

In addition, I would like to either install an inline fuse for the fuel pump, or replace the wiring where it connects to the fuse panel from the factory.

Thanks to all who replied. I consider myself lucky to have a forum like this to ask and learn.

Oh, and my next long-term project... 3/4 ton axles.