Gremlins

[Wes Harden]

Been working on my burb regularly since December, all the stuff needed after it sat for 7ish years. New master cyl, fuel hoses, tank sender, carb cleaning, add aux battery, I existing alternator didn't seem up to charging 2 batteries, light and 1 high blower, Didn't even try aux AC blower.

I purchased a brand new 74 amp cs10 alt from Amazon. Installed new alternator on the 18th, drove to gas station, parts store, freeway a bit, had to road test carb. Volt meter looked good high 13v pushing two batteries. All good park it.
Thursday I get some led instrument bulbs in mail, go out to truck stick a bulb in trans temp guage, hit the lights... Nothing main battery is flat. Put the charger on it, then leave it Friday after work.

Friday I get home, and find charger didn't like 2 amp to battery on automatic. Battery has 5.5 volt . Set it to 15 amps manual charge. Disconnect neg cable put my volt meter across neg post to neg cable, I have battery volt draw, about 11 volts with charger on. So I suspect this brand new alternator I disconnect the wires, still have same volt draw. My dumb ass didn't check the amp draw.

So I go-to fuse box unplug all the add ins, no change. Pull all the fuses, no change. I go back under hood start with the junction block on fire wall. Bingo voltage drops to almost nothing. Check wire dia for 10 gu. red wire feeds alt and horn, disconnect horn relay put wire back on junction block, and draw is back.

Disconnect alt again draw is gone. So I go and put old alt back on, crap I still have same voltage draw, finally I wise up and check the amp draw, it is .04, ok I can live with that. So I put everything back together. Replace 2 fuses I broke. Install horn relay and 2 flashers.

So it's been @ 2 hours now battery barely gets truck started, choke kicks off, idle is @850 rpm in park. Now I want to change from ported vacuum advance to manifold vacuum. Disconnect advance vacuum check my base timing @9 BTC pop manifold vacuum on to advance idle goes up to 1500ish turn the idle screw down to 850 on tach in truck, put trans in drive tach goes up to 1k and stops working wtf.

Shut off restart tach shows idle, blip throttle tach shows blip, 0ut in gear 1k and stop reading. Shut truck off, check wiring for tach under hood looks good. Start truck reads idle, in gear stops.

So I am supposed to be omw to my brother's house @60 miles away over Cajon pass, this trip is another trans road test. So pack up, gas up, coffee up, and hit the road. Tach not working at all, stuck at 1500 now, and now my turn signals aren't working. 4 ways are, so I figure the flasher took a dive.

Truck ran good, once I got pasted 138 junction and got up to speed. Seemed to cruise alitte smoother with manifold vacuum on advance.
I am hoping the fuse for the IP is crusty since I had the gaul to disturb it. I will check Saturday. But if anyone has ideas on my tach issue I would love to hear.
Thanks all rant over.

 

[obijuank5]

Damn. Have you tried setting it on fire?

 

[Bent77]

Thinking you may have missed a ground wire or two thrashing around. I'd start there

 

[tRustyK5]

Sounds like a Roadkill episode. All that's missing is to overheat three times and eventually remove the hood and strap it to the roof...

 

[diesel4me]

That 10 ga red wire from the junction block to the alt may be rubbed thru and shorting to ground on the engine block,seen many harnesses on the square bodies have that happen where they run behind the engine--sometimes the wire loses insulation where they pass thru that steel conduit going to the starter too,heat bakes the insulation and it cracks off--usually that wire has a fusible link in it too..

If we're talking a '72 or older truck,(would help if we knew the year & model!)--those had two glass fuses hidden in rubber fuse holders on each corner of the nose too,that powers the amp meter and some other interior circuits--weird things can happen when those fuses pop or they make poor contact in those rubber fuse holders,which look more like a plug & socket than a fuse holder--much like the splices GM put on the rear plate light harness..

 

[Wes Harden]

Thanks for replys. This is a 77 Silverado k20 burb, is in my signature. I see it is not attached to post.

 

[diesel4me]

I think a Suburban may have the power rear window motor wired to that junction block on the firewall too.....

 

[Wes Harden]

No power windows, I isolated draw to that one circuit. 12 hours later batt is 12.5 volts. I think I got it. I might bench check amp draw on new alt be4 I send it back, got a new 1 coming.
Now I need to sort out turn signals and tach. Turn signal flasher not it. Digging further

 

[diesel4me]

4 way flashers have constant hot feed too I think...

I've seen cobbed up trailer hitch wiring cause headaches like this before also..
I know you think you have isolated the bad circuit--just pointing out other things that stay "hot" constantly..headlamps are another!..

 

[Wes Harden]

Turn signals fixed my dumb ass replaced wrong flasher.
Checked instrument fuse it has good continuity at contacts.
Tach seem to bobble as turn signals are activated, something is not in correct place or back feeding.

 

[Wes Harden]

Appreciate it @diesel4me. I can get to looking at the trees and not see the forest.

 

[tRustyK5]

I had a draw issue with my 90 Blazer. It was the tach...

Ruined a new red optima before finding that though.

 

[Wes Harden]

Tach might be the issue now that I see interference from turn signals.
This is the real project I came over the hill to work on, buggy needs a real muffler, 1 new state regulations, and 2 I'm tried of listening to it. Got modify the engine cage/bumper to make it fit.

 

[fordsucks!]

Could be poor current flow, could be bad alternator. I would start by checking all connections, add a couple of grounds and see what happens. 1 loose clamp or terminal somewhere could be causing you all this headache....

 

[Wes Harden]

Well tach issue turned out to be crappy crusty mid loom plug just after condenser looking thing in distributor tach signal wire. Disassembled said connector wire brushed reassemble all good.
Should have the replacement Alt today see if I can get it on after work,

 

[Wes Harden]

Received my 2nd new alternator, same brand model. I took amp draw test. Negative battery cable off, 10 amp range meter connected neg post to neg cable. Original alternator has .039 amp draw, new alternator is 1.073. So I am sending this one back and try another brand.

 

[Wes Harden]

Got my 100 amp Powermaster alt yesterday, installed on truck, amp draw was .01 less than old alternator.
Powermaster was little more than 2x the 1st brand I tried, but still reasonable for a 100% new.
Main battery voltage before start up was 12.3 volts. Start up on 2nd step choke, @ 1700 rpm, voltage came up to 13.56v within the time the choke needed to drop to 3rd step, voltage up to 14.11, all of this with aux battery excluded. After adding in the auxiliary battery voltage stayed above 14v. Hi beams door open and 2 blowers on hi at normal park idle, voltage was a steady 13.66.
I am very happy with these results.
The other brand would charge both batteries but took longer to recover, and voltage was lower across board I would have been satisfied with that but for the 1+amp draw.