Wiring gauges/accessories....where do I tap in???

[thefarmboy21]

I just finished a 350 swap in my 86 K20 and need to know where to wire into. First order of business is an aftermarket tach and an oil pressure gauge. I was browsing around under the dash and noticed a clever provision for about 6 female blade plugs for small ground wires....I also noticed in the fuse box there are lots of empty, one plug slots. Some are labeled BATT, some IGN, some ACC.....I assume these are factory provisions for add ons? But 1. Where do I get the fancy little plugs to go in them and 2. What would I use for the gauges, accessory or ignition? And 3. What do I wire the backlighting into (for night driving) I don't really want them lit up all the time. Also, IF I decide to run an electric fan, what's a good way to wire that in? Thanks.....electrical is not my strong point.

[bake74]

     Go to the wiring diagrams in the tech section and look up your year of truck and look at the fuse box.  You want to make sure power is available when you want your accessories to run and not when you don't.

[Mario]

You should have a single tan wire going through your bulkhead connector that leads up to the factory gauge.  I would switch it at the bulkhead connector to lead to your new gauge.  I wouldn't try to operate both.  Assuming your truck didn't come with a factory tach, you'll need to run a single white wire from your distributor into the cab.  You might have a grommet on the firewall near your distributor.  You could go in through there or route it back to the bulkhead connector.  You could use new packard 56 connectors and an open slot on the bulkhead connector.  For backlighting, you could trace the lighting wire from the factory instrument cluster to where it gets lighting power from, or just tap into the proper wire at the light switch.  A simple flat male terminal will plug into one of the accessory slots.  Good luck Man!

[bd]

Refer to the 1986 Wiring Manual beginning page 10, as needed.

For the fuse box connectors purchase one or two American Autowire 500429 ATO fuse box kits.  They work beautifully!  I recommend that you crimp and solder the terminals to the wires, using 60/40 rosin core (electronics grade) solder.

Power the gauges from the IGN taps in the fuse box using the "clear" ATO connectors.

Assuming analog gauges, power gauge backlighting from the LPS taps in the fuse box using the "green" ATO connectors.  The LPS taps "dim" with the instrument lamps dimmer control.  [If you are using digital gauges, connect the gauge backlighting circuits to the short brown pigtail that comes right off the back of the headlamp switch].

Wire the electric engine fan through a radiator support mounted power relay (to keep the fan power leads as short as possible) that is rated for the current draw of the fan.  Fan motor battery power should run through a 10-gauge wire (red is preferred to maintain consistency with factory color codes) protected by a 14-gauge fusible link (or appropriate fuse) at the battery.  In other words, the positive fan cable should run from the battery through the circuit protection to the relay; then from the relay to the fan motor.  See "How to make a Fusible Link" by VileZambonie in our Technical Pages if you have questions on constructing a link.  Fan motor ground should connect through a 10-gauge black wire to the radiator support, sharing its attachment bolt with a 10- or 8-gauge black wire connecting directly to the battery negative terminal. 

The fan relay should be "controlled" by a thermal switch mounted in the intake manifold coolant crossover, near the thermostat housing.  You can add supplemental manual control of the relay with a toggle switch located in the cab as an option.  The "control circuit" of the relay can be powered from the "AUX A/C" tap at the top right corner of the fuse box ("gray" ATO connector); you may need to add a fuse to the "AUX HTR A/C" location to power the tap.  The AUX power tap will kill power to the fan during cranking and in the ignition switch accessory position to decrease current demand placed on the battery.

As stated, wiring can be routed through unused positions of the factory bulkhead connector using Packard 56 Series terminals.  If you anticipate an eventual need to feed many supplemental circuits through the firewall, you can install an HD30 Deutsch bulkhead connector.  Deutsch connectors are pricey, but possess a compact footprint making them a good choice for our trucks.

[Don5]

Although I did not post the original question, this old dog learned a few things. Thank you guys for sharing these tips!