What have I done with this tach?

[85k10383]

I installed a autogage 3 3/4 tach while swapping motors. The wiring was fairly straightforward, or so i thought. I spliced into the gray wire which should be the dash lights, from what i can find. The lights in the tach work perfectly, but when I turn them on the tach lights up and the rest of the dash goes dead! As in, as soon as I pull the switch, the gas gauge drops to the peg. It is the only remaining electric gauage in my truck that functions, everything else has been replaced with mechanical stuff. I also have no dash indication of turn signals, even though they are working. What have I done here? Or have i run into some more fodder for the "Stupid POs suck" thread?

 

[crazy4offroad]

I usually suspect a bad ground in situations like this. Where did you ground the tach? If you didnt ground it to some metal part of the body under the dash you may want to.

 

[85k10383]

Good idea, I'll check that out ASAP. If not I'm wondering if maybe I need to find another source for the lighting on the tach.

 

[85k10383]

Well it wasn't a ground problem that originates with wiring i have done. I re-routed the ground for the tach to good clean metal and that didn't solve the problem. I'm thinking that maybe the grounding for the OE cluster is no good and by grounding the tach I have inadvertantly grounded out the power for the cluster. I will have to (again!) disassemble te dash and check that out, but not today. After yesterdays misadventure with the grinder, I'm taking a day off!
As a side note, this has occurred along with the installation of an LMC headlight relay set-up. Since installing the relay system, the parking light position on the headlight switch no longer exists. One click out and the headlights are on! Could this be related at all or just a coincedence?

 

[crazy4offroad]

Sounds like you've found the problem, if it started after doing the relay. Maybe you have the signal/hot mixed up? Or some kind of backfeed.

 

[85k10383]

I not sure at all anymore! I noticed the trouble with the dead cluster after installing the tach. The headlight relay install is what brought the funky headlight switch to my attention. I also thinking that the OE headlight switch has **** the bed as a result of all this. I haven't got around to taking the cluster out yet, its been 100 or better the last three days and I'm staying inside.....

 

[85k10383]

Took the cluster out and discovered my trouble, I had spliced into the wrong grey wire! I'm still not sure what it was (maybe a speaker wire LOL) but re-wired it correctly and all is well! Thanks for the help again guys!

 

[Manbearpig]

Glad you figured it out man

 

[85k10383]

Thanks man! I also have now figured out what was wrong with the headlight switch. The OE harness was so corroded that it was intermittently not allowing the lights to come on at all! A little time spent replacing old rotted wiring and the problem is solved. The high-beams are still not right however. When switching them on the top two bulbs go out, and the bottom two come on. With the originalwiring all four bulbs were on in high beam. I'm not sure if this a vagary of the new harness or if there is something amiss.....

 

[Manbearpig]

Have you tried adding relays to the system?

http://www.73-87.com/7387garage/exterior/headlight_relay.htm

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[85k10383]

Yes, I did. The LMC HD harness includes relays. The failure point seems to be that the new harness piggy-backs on the old wiring whiich is somewhat suspect. I think what I may do is simply completely re-wire the headlights from switch to bulbs using as much of the LMC harness as possible. For now i have functioning high and low beams that are properly aimed so it isn't really an emergency, just something else to putz with....