HEI tach wire messing with radio
 

I posted this in the electrical section and haven't been getting any responses so I hope someone here can help.

Here's my issue. I bought a cheap Bosch tack to use to tune my fresh rebuilt 400 for my 69 bird. I needed something to set the timing and idle and didn't plan on installing it permanently in the car. I temporarily installed it during the break in to keep an eye on things but the wire from the distributor is interfering with my radio. With the tach hooked up and the car running the radio buttons sometimes don't work, it won't turn off with the power button and sometimes when I turn the car off, the volume knob don't work, the presets get screwed, and sometimes the speakers don't work. I unplug the wire from the distributor and the radio goes back to normal. I plug it in and it goes haywire again. The problem only happens with the car running, it's fine with the ignition in the on position and the car not running. I talked to the radio manufacturer and they suggested putting noise suppressing magnets on the distributor wire (I forget what they're called) so I got some and put 4 on. It helped but there were still issues with the radio. Then they suggested rerouting the wire so I tested it by running it through the driver side window but that didn't help either. It was originally routed through the firewall and behind the radio. I disconnected the tach and now my speakers turn off for a split second and makes the radio sound like a record skipping. I think it's permanently damaged. Retrosound is sending me a new radio body under warranty but I want to keep a tach in the car. I'm looking at a Stewart Warner tach to match my other gauges but don't know if I want to spend the $125 and possibly ruin another radio. I know this has to work somehow, anybody else ever have this issue in their car?

I do not think that your HEI or Tack is the issue I think that by coincidence your radio took a big static discharge hit that damaged it at the same time you where doing the Tack install!

HEI tach wire messing with radio
 

If I disconnect the tach wire from the distributor the radio worked fine. When I plugged the wire back in, the radio went haywire again. I tested it several times all with the same results. But I think it’s permanently damaged now. I’m no electrical scholar but if it took a big static discharge that damaged it, wouldn’t it be screwed up no matter if the tach was connected or disconnected?


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I'd check the grounds on the tach and radio --and also check dash ground to body and firewall to engine. Sounds like you might be getting voltage back-feeding into the radio that should be completing its circuit to ground.

This^^^ I do not think you can have too many ground straps to the chassis, engine, etc. A bad ground can give you some really crazy symptoms!

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They were both mounted to the same bracket under the dash. I can try running the tach ground somewhere else.

What kind of radio?

.

Retrosound in first post and they are sending a replacement.

He didn't mention bluetooth or remote control info.

With failed/shorted components the thing might be a geiger counter now.

Clay

It's a Retrosound Rodando and it's less than a year old. It has bluetooth and USB ports.

Where are you getting the power for the HEI?
And the radio?

I'd try a capacitor (noise suppressor) and see if that helps.


:confused:

The HEI is connected to the wiring harness and the radio is direct to the fuse box.

How would a capacitor be hooked up? Would it hook up to the radio, distributor, or tach wire?

I'm beginning to wonder if it's really worth all the trouble. I don't race the car and don't NEED a tach, I only bought it for tuning purposes. I disconnected it and it's sitting on my work bench.

Original coil would have had one at the coil probably. (inside distributor had one also)

The radio may have had one at the radio also.
Most problems were with the older equipment they were very noisy.
(even fuse box had them sometimes)

Basically they attach at the power line and to the ground.

I wonder if the HEI when firing is feeding back through the power wire to the fuse box?

See if there is a capacitor at the fuse box.


:confused:

The noise is definitely coming from the tach wire connected to the distributor/coil. That's why I took it out. Maybe the capacitor should be hooked up to that wire? I'll check the fuse box tonight.

Here's a pic of radio suppression for 69 Bird:


http://forums.maxperformanceinc.com/...1&d=1544197607


Couldn't find the one on where they added extra condensers.
I'll keep looking.


:confused:

Found a service bulletin on the fuse box.
(1970 though but should apply)


#1


http://forums.maxperformanceinc.com/...1&d=1544198569


:)

That's a page out of the service manual isn't it? I'll check that tonight too.
Thanks for the bulletin, all useful info!

Yes, 1st on is out of service manual.
The other pics may be in there also.


:)

Do not put additional capacitors on the tach wire. Make sure the radio is grounded to the dash metal well and the dash/firewall is connected well to the engine block. Route the tach wire away from the radio, in fact route it along the dash sheet metal.

George

^^^ What George said, read carefully and do both items he mentions!

I would be doing some troubleshooting by putting a meter on the Radio power leads. Read the DCV with the tach both on and off. Then read ACV the same way. Not as good as putting an O-scope on the line but may give you some clues as to what is going on.